ACPAtmospheric Chemistry and PhysicsACPAtmos. Chem. Phys.1680-7324Copernicus PublicationsGöttingen, Germany10.5194/acp-16-6223-2016Kinematic and diabatic vertical velocity climatologies from a chemistry climate modelHoppeCharlotte Marinkec.hoppe@fz-juelich.dehttps://orcid.org/0000-0002-9740-8744PloegerFelixKonopkaPaulMüllerRolfhttps://orcid.org/0000-0002-5024-9977Institute of Energy and Climate Research (IEK-7), Forschungszentrum Jülich GmbH, Jülich, Germanynow at: Institute of Energy and Climate Research (IEK-8), Forschungszentrum Jülich GmbH, Jülich, Germanynow at: Rhenish Institute for Environmental Research, University of Cologne, Cologne, GermanyCharlotte Marinke Hoppe (c.hoppe@fz-juelich.de)23May201616106223623928September20152November20152May20166May2016This work is licensed under a Creative Commons Attribution 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by/3.0/This article is available from https://acp.copernicus.org/articles/16/6223/2016/acp-16-6223-2016.htmlThe full text article is available as a PDF file from https://acp.copernicus.org/articles/16/6223/2016/acp-16-6223-2016.pdf
The representation of vertical velocity in chemistry climate models is a key
element for the representation of the large-scale Brewer–Dobson circulation
in the stratosphere. Here, we diagnose and compare the kinematic and diabatic
vertical velocities in the ECHAM/Modular Earth Submodel System (MESSy)
Atmospheric Chemistry (EMAC) model. The calculation of kinematic vertical
velocity is based on the continuity equation, whereas diabatic vertical
velocity is computed using diabatic heating rates. Annual and monthly zonal
mean climatologies of vertical velocity from a 10-year simulation are
provided for both kinematic and diabatic vertical velocity representations.
In general, both vertical velocity patterns show the main features of the
stratospheric circulation, namely, upwelling at low latitudes and downwelling
at high latitudes. The main difference in the vertical velocity pattern is
a more uniform structure for diabatic and a noisier structure for kinematic
vertical velocity. Diabatic vertical velocities show higher absolute values
both in the upwelling branch in the inner tropics and in the downwelling
regions in the polar vortices. Further, there is a latitudinal shift of the
tropical upwelling branch in boreal summer between the two vertical velocity
representations with the tropical upwelling region in the diabatic
representation shifted southward compared to the kinematic case. Furthermore,
we present mean age of air climatologies from two transport schemes in EMAC
using these different vertical velocities and analyze the impact of residual
circulation and mixing processes on the age of air. The age of air
distributions show a hemispheric difference pattern in the stratosphere with
younger air in the Southern Hemisphere and older air in the Northern
Hemisphere using the transport scheme with diabatic vertical velocities.
Further, the age of air climatology from the transport scheme using diabatic
vertical velocities shows a younger mean age of air in the inner tropical
upwelling branch and an older mean age in the extratropical tropopause
region.
Introduction
The numerical representation of vertical velocity in meteorological models
can be established in various ways. The implemented vertical velocity
representation depends on the vertical grid structure of the model. Various
coordinate systems can be used to define vertical model layers, such as
pressure p or potential temperature θ, with respective vertical
velocities ω=DpDt and
θ˙=DθDte.g.,.
Hence, in chemistry climate models (CCMs), different vertical velocity
representations may be used for the advection of chemical trace gases, a fact
which needs to be considered when comparing modeled trace gas distributions.
If a pressure-based vertical coordinate system is implemented, the associated
vertical velocity ω is calculated as a residual from the horizontal
flux divergence using the continuity equation. This method is denoted
kinematic vertical velocity representation and most commonly used in
CCMs.
The potential temperature θ can also be used as the vertical
coordinate in a model, forming isentropic vertical model layers. Usage of
θ is especially suitable in the stratosphere, where the flow mainly
propagates along isentropic surfaces e.g.,. In
this configuration, vertical velocities are derived from diabatic heating
rates. The corresponding vertical velocity θ˙ is referred to as
diabatic vertical velocity.
In a perfect model, all vertical velocity representations would deliver the
same result. However, inaccuracies are always present in numerical models.
They occur due to numerical discretization of the underlying equations,
limited accuracy of representation of numbers in computers, and
parametrizations of sub-grid scale processes. These inaccuracies lead to
differences in vertical velocity fields when using different vertical
velocity representations. There are typical patterns that occur in the
vertical velocity distributions of the aforementioned numerical
representations. One example is noisy small-scale structures in the
kinematic vertical velocity field, as reported by and
, although their results also contain some effects from the data
assimilation scheme.
The horizontal discretization also has an impact on the simulated vertical
velocity field. In this study we consider the chemistry climate model
ECHAM/Modular Earth Submodel System (MESSy) Atmospheric Chemistry EMAC; and find
that the vertical velocity may even differ between the dynamics and the
transport scheme in the same CCM. In the EMAC model, the tracer transport is
calculated on a regular grid structure, while the model dynamics is
calculated in spectral representation. Consequently, the vertical velocity
used for tracer transport differs from the vertical velocity in the dynamical
core.
It is difficult to validate model results for large-scale, stratospheric
vertical velocity, as this quantity cannot be measured directly. In the
atmosphere, vertical velocities are much smaller than horizontal velocities,
except for fast convection events. Thus, modeled vertical velocity can only
be compared to the vertical velocity from reanalyses, like ERA-Interim
from the European Centre for Medium-Range Weather Forecasts
(ECMWF). However, vertical velocities in reanalysis themselves suffer from
large inaccuracies e.g.,.
To overcome the problem of observability of vertical velocity, trace gas
observations from satellite remote sensing instruments are compared to
modeled trace gas distributions. However, the interpretation of the
differences of the distributions should be handled with care, since those
tracer distributions result from several different processes in the
atmosphere, namely, advective transport, mixing, and chemical reactions. In
particular, for mean age of air (the average transit time of an air parcel
through the stratosphere) both advective transport and mixing are involved
. Thus, precise knowledge of the vertical velocity is
crucial for the analysis of stratospheric trace gas and age of air
distributions to distinguish between advection and mixing effects.
Considering only trace gas distributions does not allow for residual transport
and mixing to be differentiated.
This work presents diagnostics to obtain the vertical velocity of the tracer
transport scheme in the CCM EMAC , and in the coupled
model system EMAC–CLaMS (Chemical Lagrangian Model of the Stratosphere) in Sect. . Monthly
and annual zonal mean climatologies of kinematic and diabatic vertical
velocities in EMAC are shown and the characteristics of each vertical
velocity representation are discussed in Sect. . The
influences of the vertical velocity on age of air distributions are
investigated and the possibilities and limitations of the mean age of air
diagnostic are discussed in Sect. . Conclusions are given in
Sect. .
Theory: vertical velocity representations
This section describes the calculation of the kinematic and diabatic vertical
velocity in the framework of the coupled model system EMAC–CLaMS
. This model system consists of the EMAC and the CLaMS .
EMAC–CLaMS contains diagnostics for kinematic and diabatic vertical
velocities to serve as input to the tracer transport scheme. The two vertical
velocity diagnostics are calculated simultaneously in grid-point space during
the same model run; thus, the model setup such as radiation, trace gases for
radiation input, and resolution of the model grid, are identical.
Kinematic vertical velocity
The standard vertical velocity in EMAC is derived from the spectral advection
scheme in ECHAM5. The vertical wind η˙=DηDt in ECHAM5 is calculated from the zonal and meridional
horizontal winds using the continuity equation:
∂∂η∂p∂t+∇⋅vh∂p∂η+∂∂ηη˙∂p∂η=0.
Here, η denotes the terrain following hybrid pressure-based vertical
coordinate in ECHAM5 see. vh is the
horizontal wind vector on an ECHAM5 model layer and ∇ the horizontal
gradient operator. After the advection time step, the new surface pressure is
calculated for each grid box, which determines the pressure levels of the
hybrid model grid for the next time step. The vertical velocity η˙
(a diagnostic output variable from the spectral representation) mapped into
a pure pressure vertical coordinate system will be denoted
ωspec in the following.
The kinematic method implies fundamental problems since the horizontal wind
speed in the atmosphere is much higher than the vertical wind speed. As
a result, small errors in the horizontal wind may lead to large errors in the
vertical wind. Vertical wind fields derived through the continuity equation
often show very patchy structures. This phenomenon has been shown to cause
excessively dispersive transport e.g.,although their results are also
affected by assimilation effects.
In the standard configuration of EMAC, an implementation of a flux-form
semi-Lagrangian transport scheme FFSL; is used for
the tracer transport. Only the horizontal winds are input parameters for the
tracer transport in EMAC. Horizontal tracer mass fluxes are derived using the
horizontal wind field. The vertical velocity ωFFSL used in
the FFSL tracer transport is derived from the continuity equation for the
tracer from the horizontal tracer mass fluxes for individual model grid boxes
. This vertical velocity ωFFSL differs
from the vertical velocity ωspec deduced from the wind field,
since different advection schemes are used for the air-mass density and for
trace gases: the spectral advection is used for air-mass density, whereas the
grid-point-based FFSL transport is used for the tracers. Each advection
scheme uses its own grid and is internally mass-conservative, but re-mapping
of trace gas distributions to the η-grid can produce inconsistencies.
This phenomenon has been investigated in detail by .
Annual, zonal mean ω‾spec (top left panel)
and ω‾FFSL (top right panel) (hPaday-1)
for the year 2005. Here, black solid lines show the 0 hPaday-1
contour of the respective vertical velocities. The bottom panels show
absolute value of absolute difference (hPaday-1) (left) and
relative difference (right) between ω‾spec and
ω‾FFSL. White dashed and solid lines in the bottom
panels display the 0 hPaday-1 contour of
ω‾spec and ω‾FFSL,
respectively.
Within the frame of this work, a diagnostic for vertical velocities was
developed and implemented in the EMAC flux-form semi-Lagrangian transport
module. The diagnostic for the vertical velocity in the transport scheme is
adapted from the Community Atmosphere Model (CAM) finite-volume dynamical
core (implemented by C. Chen, and described in ). The internal
grid in the FFSL transport module differs from the η-grid in ECHAM5: it
is variable in the vertical dimension and fixed in the horizontal dimensions.
This concept is denoted as “vertically Lagrangian” or
“floating Lagrangian vertical coordinate” . In each advection
time step, horizontal mass fluxes through the lateral boundaries are
calculated for each grid box. Through the advection the mass in each grid box
changes and therefore also the thickness of each grid box in
a terrain-following pressure-based vertical coordinate system. For the
ω-diagnostic the pressure at the layer interfaces before and after the
advection is compared. The pressure in one grid box is influenced by the mass
in the grid boxes above and by the horizontal mass fluxes into the grid box.
This constitutes the vertically Lagrangian character of the advection scheme,
since the pressure boundaries of the grid boxes are not fixed. After the
advection time step, the new surface pressure based on the new mass
distribution in each column of the model grid is calculated. Then, a vertical
re-mapping of the trace gas distributions according to the η-levels
defined by the new surface pressure takes place.
The top panels of Fig. present the annual, zonal mean of the
vertical velocity from the spectral representation
ω‾spec and from the transport diagnostic
ω‾FFSL. The differences between
ω‾spec and ω‾FFSL are
visualized by showing the absolute values of their absolute and relative
differences. The absolute value of absolute difference was derived as
|ω‾spec-ω‾FFSL|, and the
absolute value of the relative difference is defined as |ω‾spec-ω‾FFSL0.5⋅(|ω‾spec|+|ω‾FFSL|)|.
The comparison of the vertical velocity ω‾spec to
ω‾FFSL reveals that the differences are rather small
in most parts of the stratosphere. There are some exceptions of small regions
with high relative differences: the minimum in the upwelling pattern at
the Equator at 10 hPa is stronger in ω‾spec, showing
even positive values in the annual, zonal mean. Further, the upwelling and
downwelling regions are slightly shifted around the
contours of 0 hPaday-1. Apart from that, the relative
differences between ω‾spec and
ω‾FFSL are below 10 % (bottom right panel
of Fig. ). The absolute differences in the annual zonal mean are
small throughout the stratosphere (bottom left panel of Fig. ).
In the following analysis the vertical velocity ωFFSL obtained
from the new diagnostic in the transport scheme is used since this is the
actual vertical velocity that causes vertical advection in the FFSL transport
scheme. In the following, ωFFSL will be denoted ω.
Transformed Eulerian mean
The calculation of the Eulerian zonal mean ω‾ of the
kinematic vertical velocity ω does not deliver a meaningful
representation of the atmospheric diabatic circulation that is relevant for
trace gas transport. Planetary waves may induce upwelling and downwelling in
the Eulerian zonal mean ω‾ in different latitudes, which is
not related to net tracer transport. In this situation, calculating the
Eulerian zonal mean of ω yields zonal mean upwelling and downwelling
in different latitudes due to the planetary wave activity, which is not
related to net tracer transport (see Fig. ). A more detailed
discussion of this phenomenon is given in, e.g., .
Annual, zonal mean vertical velocity w‾
(ms-1) (top panel) and transformed Eulerian mean (TEM) vertical
velocity w‾* (ms-1) (bottom panel) from EMAC for
the year 2005. Dotted lines display potential temperature levels (K). The
vertical axis displays log-pressure height (km), calculated from
Eq. ().
The transformed Eulerian mean (TEM) can be used instead of the Eulerian mean
to avoid the misleading effects in the zonal mean vertical velocity. The idea
of this transformation is to produce a similar picture as if the average
vertical velocity was taken along fluid parcel paths. Another idea of this
transformation is to find a correct representation of the diabatic vertical
velocity in the p space by an appropriate redefining of v* and w* and
without changing the continuity equation for v* and w*. The TEM mean
meridional velocity v‾* and vertical velocity
w‾* are defined as follows e.g.,:
v‾*=v‾-1ρ0ρ0v′θ′‾θz‾z,w‾*=w‾+v′θ′‾cosϕθz‾ϕ.
Here, v‾ denotes the Eulerian mean meridional velocity,
w‾ the Eulerian mean vertical velocity in log-pressure
coordinates, v′θ′‾ the eddy heat flux, θ‾
the Eulerian mean potential temperature, subscript z denotes the partial
derivative in the vertical (∂∂z), and ϕ
latitude. ρ0(z)≡ρ0⋅e-z/H is the basic mass
density with ρ0 denoting the mass density at the reference surface
pressure p0. The log-pressure height z is derived from pressure p
through
z=-H⋅lnpp0.
In this study, surface pressure p0 and scale height H were set to
1000 hPa and 7 km, respectively. The circulation described by
v‾* and w‾* is called the residual mean mass
circulation.
Figure shows the zonal mean vertical velocity w‾ and
the TEM vertical velocity w‾* from
EMAC for the year 2005. The zonal mean vertical velocity w‾ in
the top panel of Fig. features a pronounced downwelling in the 40
to 60∘ latitude region and an upwelling in the polar regions from
60∘ latitude to the poles in both hemispheres. This pattern is due to
eddy flux divergences and the zonal mean w‾ thus gives a very
misleading picture. The TEM vertical velocity w‾* in the
bottom panel of Fig. represents the relevant circulation for
zonal mean tracer transport. Here, the circulation shows downwelling
throughout the entire extratropical stratosphere in the annual mean, as
expected.
Diabatic vertical velocity
In EMAC–CLaMS potential temperature is used as the vertical coordinate in the
stratosphere . The vertical velocity θ˙ in this
representation is derived from the diabatic heating rate Q:
θ˙=QθT.
Here, diabatic heating rate means Q=J/cp, where J is the diabatic
heating rate per unit mass and cp the specific heat capacity at constant
pressure. Transport across isentropic surfaces can take place only through
diabatic heating. The diabatic heating rate Q is the sum of radiative
heating Qrad, heating from diffusion and turbulent mixing
Qdiff and heating from latent heat release Qlat:
Q=Qrad+Qdiff+Qlat.
The radiative heating Qrad is the dominant term in the
stratosphere, while in the tropopause region the latent heat release is also
of importance . The contributions of the different terms to the
diabatic heating rate in the ERA-Interim reanalysis were also investigated by
and .
A diagnostic tool to capture the diabatic heating from the different process
parametrizations in EMAC was implemented during this work. A slightly
modified version of the tendency diagnostic of the ECHAM6 model
was used for this task (S. Rast, personal communication, 2013). The
diagnostic reads the temperature before and after processes that cause
diabatic heating and calculates temperature tendencies ΔT
(Ks-1). Let ΔT(i) be the temperature tendency caused
by process i. If temperature T at time t is changed by n different
processes in the model time step Δt, then the temperature in the next
time step T(t+Δt) reads
T(t+Δt)=T(t)+∑i=1nΔT(i)(t)Δt.
The temperature tendencies ΔT(i) from all processes that cause
diabatic heating are added up. The vertical velocity θ˙ is then
determined by Eq. (). In EMAC, the parametrizations for
radiation, convection, clouds, vertical diffusion, and gravity wave drag
contribute to the total diabatic heating rate Q. Most of the processes
mentioned above cannot be resolved by the coarse model grid and have to be
parametrized. However, subgrid parametrizations always imply a certain degree
of inaccuracy. Different parametrizations of the same process deliver
different results. For example the choice of the convection scheme influences
the diabatic vertical velocity in the tropical tropopause region (TTL; see
Appendix ). For this study, the parametrizations of subgrid
processes were set to the standard EMAC configuration (see
Table ).
Parametrizations in EMAC.
ProcessSchemeCloudsECHAM5 cloud schemeand references thereinConvectionTiedtke convection with Nordeng closureGravity wavesHines scheme RadiationECHAM5 radiation scheme* (,, and references therein)
* EMAC prognostic water vapor and cloud
forcing is used. The other radiative forcing is not prognostic. O3 is
taken from the climatology of . The following trace gases are
set to a constant value for the year 2000 in the troposphere with a linear
decay in the stratosphere: CO2, CH4, N2O, CFC-11,
CFC-12.
Vertical velocity climatologies
This section presents zonal mean climatologies of diabatic and kinematic
vertical velocity in EMAC and analyzes the differences between these vertical
velocity representations. These zonal mean climatologies for
ω‾ were produced by interpolating the model data (mean
values over the model time step of 15 min) onto a regular vertical
grid in θ coordinates and calculating the zonal mean value over the
10-year simulation. For this comparison, both velocities have been
converted to comparable quantities (namely,
ω=DpDt). The kinematic vertical velocity
w‾* (defined in the log-pressure coordinate system and
calculated in the TEM formalism) has been converted to
ω‾* in pressure coordinates using the definition of the
log-pressure height (Eq. ):
ω‾*=-w‾*⋅pH.
Equation () is only valid for model layers of constant
pressure p. The EMAC hybrid model layers are defined such that above about
55 hPa the pressure at the model layers is constant.
The diabatic vertical velocity θ˙ was converted to the respective
velocity ω‾θ in pressure coordinates by using the
definition of the total derivative of θ in spherical coordinates:
DθDt=∂θ∂t+1rEu∂θ∂λ+1rEcosϕv∂θ∂ϕ+ω∂θ∂p.
Here, λ, ϕ, and rE denote longitude, latitude, and
the radius of the Earth, respectively. Solving Eq. () for
ω leads to
ωθ=-∂θ∂t-1rEu∂θ∂λ-1rEcosϕv∂θ∂ϕ+θ˙∂θ∂p.
The robustness of this transformation has been checked by first applying
Eq. () and then using the inverse transformation to convert
ωθ to θ˙test. The differences between the
original θ˙ and θ˙test are found to be
smaller than 10-6K (not shown). used this
transformation (Eq. ) in a similar way.
Diabatic vertical velocity ω‾θ from
diabatic heating rates (top left panel) and transformed Eulerian mean (TEM)
vertical velocity ω‾* (top right panel) from
10-year EMAC climatology (Paday-1). The bottom panels
show absolute value of absolute difference (Paday-1) (left) and
relative difference (right) between ω‾θ and
ω‾*. Dashed and solid black contours indicate the
turnaround latitudes of ω‾θ and
ω‾*, respectively. Dotted lines display levels of
constant potential temperature θ.
This section presents a comparison of the annual, zonal mean of the diabatic
vertical velocity ω‾θ calculated from
Eq. () and the kinematic vertical velocity
ω‾* according to the TEM formulation in the 10-year EMAC
simulation, whereas monthly climatologies are presented in
Appendix . Figure presents respective
climatologies for the seasons December to February and June to August.
Figure shows that the 10-year mean of both vertical velocity
representations exhibits continuous upwelling at low latitudes and continuous
downwelling at higher latitudes and in the polar regions.
The relative and absolute differences between ω‾θ
and ω‾* are also presented in Fig. . There
are notable differences in the shape of the upwelling region (tropical pipe):
the turnaround latitudes in both hemispheres of ω‾* are
nearly constant with height up to 2 hPa, so that the tropical pipe in
the kinematic vertical velocity field is almost straight. In contrast, the
tropical pipe of the diabatic vertical velocity ω‾θ
has a different shape. It is wider than the upwelling region of
ω‾* up to 20 hPa and narrower at higher
altitudes. In Fig. the turnaround latitudes of
ω‾θ and ω‾* can directly be
compared to each other. At 2 hPa the turnaround latitudes of the
diabatic velocity are located at 35∘ latitude while they are found at
40∘ latitude in the kinematic velocity field. The different shape of
the tropical upwelling region causes the largest relative differences between
ω‾θ and ω‾* (bottom right panel
of Fig. ), though the absolute differences around the
turnaround latitudes above 600 K are small (bottom left panel of
Fig. ).
The upwelling at around 50 hPa extends to higher latitudes in
ω‾θ in both hemispheres, i.e., from 40∘ S to
42∘ N in ω‾θ compared to 35∘ S to
37∘ N in ω‾*. The upwelling is stronger in the
diabatic vertical velocity field in the latitude range between 30 and
40∘ in both hemispheres.
Diabatic vertical velocity ω‾θ from
diabatic heating rates (top panels) and transformed Eulerian mean (TEM)
vertical velocity ω‾* (bottom panels) from 10-year EMAC
climatology (Paday-1) for the seasons December to January (left
panels) and June to August (right panels). Solid black contours indicate the
turnaround latitudes of ω‾θ (top panels) and
ω‾* (bottom panels). Dashed contours in the bottom panels
display the respective turnaround latitudes of ω‾θ.
In general, the circulation pattern is more uniform using diabatic vertical
velocities. The kinematic vertical velocities exhibit more structures, even
in the 10-year zonal mean, than the diabatic vertical velocity. In
particular, the kinematic vertical velocity shows an equatorial minimum,
a minimum in downwelling at 75∘ S, and a minimum in upwelling at
30∘ N between 1000 and 1200 K. The minimum at 55 hPa
or 500 K over the Equator is also present in the ERA-Interim
reanalysis and in other climate models using
kinematic vertical velocity. At higher altitudes, directly at the Equator the
mean kinematic vertical velocity ω‾* is lower than at
10∘ latitude. This is visible, e.g., in the -3 Paday-1
contour of ω‾* at 1300 K over the Equator in the
top right panel of Fig. . The equatorial minimum is not seen in
the 10-year mean in the diabatic vertical velocity pattern. The diabatic
vertical velocity shows maximum values around 0∘ latitude and
therefore stronger upwelling above the Equator than the kinematic vertical
velocity. The differences due to the minima of ω‾* are
clearly visible in the absolute and relative difference patterns (bottom
panels of Fig. ). The noisier structure of
ω‾* compared to ω‾θ is more
pronounced in monthly climatologies (see Appendix ).
Kinematic vertical velocity (ω‾*, dashed lines)
and diabatic vertical velocity (ω‾θ, solid lines)
for February (left panel) and July (right panel) in the 10-year climatology.
Different contours for selected velocity values are shown:
0 Paday-1 (grey), -5 Paday-1 (violet),
-7 Paday-1 (orange), and -12 Paday-1
(turquoise).
Above 15 hPa, the tropical pipe is wider in ω‾*
than in ω‾θ but the region of the strongest
upwelling is narrower. This is indicated by the -3 Paday-1
contour in the top panels of Fig. . While this contour is
nearly symmetric in the diabatic vertical velocity field, it has a maximum at
10∘ N in the kinematic representation. At lower altitudes at about
15 hPa, both velocity patterns show a maximum upwelling in the
Southern Hemisphere (SH). This is a realistic representation of the diabatic
circulation, since the maximum upwelling is observed during Northern Hemisphere (NH) winter, where strong wave activity is observed in the NH
. Downwelling in the polar vortex regions is stronger using
diabatic vertical velocity. The absolute differences between
ω‾θ and ω‾* are large in the
polar regions. This is visible in Fig. since the
10 Paday-1 contour is located at higher altitudes in
ω‾θ in the region from 60∘ latitude to the
pole in both hemispheres. Additionally, the seasonal plots in
Fig. display the differences in downwelling in the polar
vortex regions.
One important difference between the kinematic and the diabatic vertical
velocity representation is illustrated in the left panel of
Fig. . This contour plot shows selected isolines of zonal mean
upwelling velocities of the two transport schemes for February. This figure
reveals that the upwelling in NH winter (here: February) in the SH tropics is
stronger using diabatic vertical velocities than when using kinematic
vertical velocities. This difference in the vertical velocities has an impact
on the simulated trace gas and age of air patterns (Sect. ).
The contour plot in the right panel of Fig. shows the
corresponding isolines of zonal mean upwelling velocities for July. It is
clearly visible that the region of the strongest upwelling in
ω‾θ is shifted southwards compared to the upwelling
region of ω‾* above 15 hPa. The
-5 Paday-1 isoline reveals that the maximum upwelling region
in the diabatic vertical velocity field is shifted southwards by about
5∘ compared to the kinematic vertical velocity. The
-12 Paday-1 isoline of the diabatic vertical velocity also
exhibits a southward shift in the NH upwelling region. This shift has a large
impact on trace gas distributions, as will be shown in the following.
To summarize, the kinematic and the diabatic vertical velocities in EMAC show
roughly similar seasonal variations. The main differences between these two
vertical velocity representations are
a noisier kinematic vertical velocity pattern
higher diabatic vertical velocities in the upwelling regions in the inner
tropics and in the downwelling regions in the polar vortex
a southward shift of maximum upwelling in the diabatic vertical velocity in NH summer
a narrower upwelling region in the zonal mean diabatic vertical velocity.
Impact on mean age of air distributions
This section shows mean age of air climatologies from a 10-year time-slice
simulation with the coupled EMAC–CLaMS model. The setup is described in
detail by . In this simulation, two transport schemes using
different vertical velocities were applied with two similar tracer sets
including a mean age of air tracer for details see,
implemented as a passive tracer with a linearly increasing lower boundary
condition “clock-tracer”;. The mean age at a certain
position in the atmosphere is derived from the difference between the local
tracer value and the current value at the surface. Tracer distributions
calculated with the Lagrangian CLaMS transport scheme (with diabatic vertical
velocity) are compared to tracer fields derived from the FFSL transport (with
kinematic vertical velocity) in EMAC. The transport with the full-Lagrangian
transport scheme will be referred to as “EMAC–CLaMS” in the following, and
the one using the FFSL transport will be denoted “EMAC–FFSL”.
Figure shows zonal mean age of air climatologies for EMAC–FFSL
and EMAC–CLaMS. Both age of air distributions are consistent with the known
features of the stratospheric Brewer–Dobson circulation. Young air masses
are present at low latitudes due to upwelling in the tropical pipe. At high
latitudes, the air is older with age of air values higher than
4.75 years in the annual, zonal mean.
Annual, zonal mean age of air from 10-year climatologies (years) for
EMAC–FFSL (top panel) and EMAC–CLaMS (middle panel). Dashed lines show levels
of constant potential temperature θ. Absolute differences in age of
air (EMAC–CLaMS - EMAC–FFSL) (years) are shown in the bottom panel. Blue
colors indicate younger air in EMAC–FFSL, while red colors indicate younger
air in EMAC–CLaMS.
In addition, the results of an analysis of the residual circulation transit
times (RCTTs) analysis are presented. This method determines
the age of air that would be present if there was only residual circulation
without any eddy mixing present in the atmosphere. The kinematic and the
diabatic vertical velocities serve as input for the RCTT analysis and the
results are shown in Fig. . Residual circulation trajectories
for kinematic vertical velocity were calculated in pressure coordinates,
where diabatic trajectories were calculated in potential temperature
coordinates using the isentropic mass-weighted residual circulation
e.g.,. Evidently, the faster residual circulation of the
diabatic vertical velocities in EMAC–CLaMS lead to lower RCTTs in most parts
of the stratosphere. Also, the transition to higher RCTTs happens at lower
latitudes using EMAC–CLAMS.
Residual circulation transit times (RCTTs) for EMAC–FFSL (top panel)
and EMAC–CLaMS (middle panel) (years). Absolute differences in RCTTs
(EMAC–CLaMS - EMAC–FFSL) (years) are shown in the bottom panel. Blue
colors indicate lower RCTTs in EMAC–FFSL, while red colors indicate lower
RCTTs
in EMAC–CLaMS.
In the following, the differences in the age of air patterns of EMAC–CLaMS
and EMAC–FFSL (bottom panel of Fig. ) will be discussed. Several
differences in the age of air distributions are consistent with the vertical
velocity differences that are discussed in the previous section. By showing
the age of air climatologies and results from the RCTT analysis, this section
discusses to what extent mean age of air distributions allow for conclusions on
the residual circulation to be drawn. Similarities in the difference patterns
of age of air and RCTTs (shown in the bottom panels of Figs. and
, respectively) indicate that differences in the age of air
pattern are due to differences in the residual circulation, whereas different
patterns show that the differences in age of air are due to mixing effects.
Note that a difference between mean age and RCTT is indicative for both
large-scale eddy mixing and small-scale diffusion effects
e.g.,.
There are notable differences in the age of air pattern between EMAC–CLaMS
and EMAC–FFSL (bottom panel of Fig. ). The most obvious pattern
in the age of air differences is the hemispheric age difference at altitudes
from 50 to 5 hPa. Here, the usage of EMAC–CLaMS results in younger
air in the SH and older air in the NH compared to EMAC–FFSL see
also. The RCTT analysis shows no analogous hemispheric pattern
and, therefore, the additional effects of mixing are the main cause for the
hemispheric pattern in mean age of air. The northward shift of the maximum
upwelling in the kinematic vertical velocity field of EMAC–FFSL compared to
the diabatic upwelling of EMAC–CLaMS (right panel of Fig. ) is
most pronounced at altitudes above 15 hPa. Thus, related differences in the
vertical velocities only have a minor contribution limited to the upper part
of the difference pattern at 10 hPa from 20∘ S to 20∘ N,
where the absolute values of the RCTT differences are higher in the SH than
in the NH.
In the inner tropics from about 10∘ S to 10∘ N latitude
above 50 hPa, the mean age of air is younger in EMAC–CLaMS, as
expected from higher diabatic vertical velocities in this region (left panel
of Fig. ). This is confirmed in the RCTT analysis, since here,
the RCTTs are clearly lower in EMAC–CLaMS.
The age of air is younger in EMAC–FFSL in the extra-tropical lowest part of
the stratosphere (below 50 hPa). This effect is likely due to a lower
permeability of the tropopause in EMAC–CLaMS causing reduced cross-tropopause
diffusion for Lagrangian transport. The RCTT analysis shows that this is a
result of mixing, since this pattern is not visible in the RCTT differences
between EMAC–CLaMS and EMAC–FFSL.
Thus, there are two distinct features of the transport schemes (EMAC–FFSL and
EMAC–CLaMS) that are responsible for the different distributions of mean age
of air. The first feature is the use of different vertical velocities due to
different vertical coordinates. Second, the different transport schemes lead
to diverse mixing properties of transport e.g.,. Only
by considering both aspects, all differences in the global, zonal mean age of
air distributions of EMAC–FFSL and EMAC–CLaMS can be explained. The vertical
velocity obtained by the method presented in this paper is valuable for
further analyses like the RCTT diagnostic, which is able to determine the
relative contributions of vertical velocity (residual circulation) and
additional mixing processes on mean age of air.
Conclusions
This work presents climatologies of kinematic and diabatic vertical
velocities from the chemistry climate model EMAC–CLaMS. The diagnostics to
obtain the vertical velocities from this model are described in detail.
Annual and monthly zonal mean climatologies of kinematic and diabatic
vertical velocity are presented. An analysis of these climatologies reveals
several differences between kinematic and diabatic vertical velocity in EMAC:
the kinematic vertical velocity field is more noisy and has several minima in
the zonal mean distribution. In contrast, the diabatic vertical velocity
field is more uniform, and shows higher vertical wind speed in the upwelling
region in the inner tropical pipe and the downwelling regions in the polar
vortex. There is a shift of the region of maximum upwelling, in particular in
boreal summer: the upwelling region is shifted southwards in the diabatic
vertical velocity field compared to the kinematic vertical velocity.
The vertical velocity fields have an impact on age of air and trace gas
distributions. This work presents a comparison of age of air distributions
that were computed using different transport schemes, and using kinematic
vertical velocity or diabatic vertical velocity. In some regions, like the
upwelling region in the inner tropics, there is a clear correlation between
vertical velocity and age of air. However, globally, mixing processes in the
atmosphere are equally important. In this study we found that the hemispheric
difference pattern in mean age of air is mainly due to mixing effects. Thus,
to compare the residual circulation in different CCMs, a comparison of age of
air or trace gas distributions alone is not sufficient. Instead, the vertical
velocity must be diagnosed explicitly to obtain information about the
residual circulation in the model.
Convection parametrizations in diabatic vertical velocity
To investigate the impact of the convection scheme on vertical velocity,
simulations were run with different convection schemes for the year 2005.
Figure shows the annual zonal mean of the diabatic vertical
velocity in EMAC using three different convection schemes, namely, the
standard Tiedtke convection scheme , the operational ECMWF
convection scheme , and the Zhang–McFarlane–Hack (ZFH)
convection scheme . The figure focuses on the region of
the tropical tropopause layer (TTL), which is the crucial region for
tropospheric air entering the stratosphere. In this region, the vertical
velocity is small compared to other regions of the atmosphere and small
differences in upwelling have a large impact on the trace gas transport. All
other process parametrizations are unchanged. The ECMWF convection leads to
the strongest vertical upwelling in the tropics. The ZFH convection shows the
weakest upwelling, and the strength of upwelling in the Tiedtke convection
scheme is in between the other two convection schemes. Another difference is
found in the strength of the transport barrier at the level of zero radiative
heating at about 350 K. The Tiedtke and the ECMWF convection scheme
lead to a strong barrier to vertical transport with an extensive layer of
negative vertical velocities in the annual mean at approximately
350 K. However, this transport barrier is not present throughout the
year and thus upward transport into the stratosphere is not completely
inhibited. In some seasons, there are regions with positive vertical
velocities at this altitude. Further, in a model simulation, there will still
be an exchange of tropospheric and stratospheric air
through vertical numerical diffusion, if the layer of negative vertical
velocities is sufficiently thin. The ZFH convection does not show the layer
with negative vertical velocities extending throughout the tropics in the
annual mean. Here, at 5∘ S and 5–10∘ N the annual mean has
small positive values of the vertical velocity. Overall, there are clear
differences in the TTL region using different convection schemes, with the
Tiedtke and ECMWF convection showing stronger upwelling between 300 and
340 K and a more pronounced transport barrier at the level of zero
radiative heating (≈350K) than the ZFH convection. The
influence of choice of convection scheme in EMAC on the hydrological cycle is
analyzed in detail in . The authors find that the tested
convection schemes show varying skill levels for different aspects of the
simulation. Thus, they do not give a recommendation for a specific convection
scheme. In the present work, the Tiedtke parametrization is used.
The diabatic vertical velocity using the Tiedtke parametrization has been
compared to the respective diabatic vertical velocities that result from the
ECMWF and ZFH convection schemes. Note that the convection experiments shown
here are only run for 1 year for demonstration purposes, and thus do not
ensure a statistically robust comparison. Figure shows the
absolute value of absolute differences of diabatic vertical velocity in a way
that the plot can be compared to the differences in Fig. ,
bottom left panel. The comparison shows that the differences between the
diabatic vertical velocities resulting from Tiedtke and ECMWF convection are
in the same order of magnitude as the differences between diabatic and
kinematic vertical velocity in the lower part of the tropical pipe between
30∘ S and 30∘ N at 50 hPa. At the Equator, the difference
pattern reaches up to 10 hPa. The differences between the diabatic vertical
velocities resulting from Tiedtke and ZFH are smaller and distributed over
the latitudes.
Annual, zonal mean of diabatic vertical velocity θ˙
(Kday-1) in EMAC for the year 2005 using the standard Tiedtke
convection scheme (left panel), the ECMWF convection scheme (middle panel),
and the ZFH convection scheme (right panel).
Absolute value of absolute differences in diabatic vertical velocity
(Pa day-1) between the standard Tiedtke convection scheme and the ECMWF
convection scheme (left panel) and between the standard Tiedtke convection
scheme and the ZFH convection scheme (right panel) in EMAC for the year
2005.
Monthly climatologies of diabatic and kinematic vertical velocity
This section presents zonal mean diabatic vertical velocities
ω‾θ and kinematic vertical velocities
ω‾* from the 10-year simulation climatology for each
month (see Figs. and ). The seasonal cycle
in the stratospheric circulation is clearly visible in both vertical velocity
representations. The most remarkable difference between the two transport
schemes is the more uniform upwelling and downwelling of
ω‾θ. This feature is more clearly visible in the
monthly mean than in the annual mean, since the ω‾* is
much more noisy in the monthly mean compared to the annual mean even when
considering a 10-year climatology. The kinematic vertical velocity
ω‾* exhibits several minima in the upwelling and
downwelling regions which do not appear in the diabatic
ω‾θ. The most pronounced minimum in the upwelling of
ω‾* is located at the Equator at 55 hPa. This
minimum is visible in all seasons. In May to July and in December the mean
values are even positive, which means downward transport at the Equator in
ω‾*. At higher altitudes, the kinematic upwelling
directly at the Equator is also weaker than the surrounding upwelling at
around 10∘ N or 10∘ S. In the diabatic vertical velocity
field, the minimum at 55 hPa is barely visible. There is a hint of
lower values at this location in the monthly means of
ω‾θ from May to July. In contrast to
ω‾*, maximum vertical velocities are located at the
Equator in several months in the diabatic representation (e.g., October).
There are also other structures of weaker vertical velocity in the kinematic
ω‾* velocity field. Minima in the downwelling regions are
also present in the kinematic vertical velocity. In the SH polar region,
a minimum in downwelling is visible from June to September throughout the
whole altitude range of the stratosphere at 70∘ S. From June to
August, this feature is also present in the diabatic vertical velocity field,
but there the minimum is less distinct and the downward vertical velocity is
higher than in ω‾*. In NH winter, the minimum vertical
velocities are visible at high latitudes polewards from 80∘ N. This
weaker downwelling occurs in the kinematic ω‾* from
November to February. In the zonal mean of ω‾θ, the
minimum at the pole is less pronounced and lasts only from December to
January.
In the regions around the addressed minima in the vertical velocity pattern
of ω‾*, the surrounding areas often show higher vertical
velocities than the diabatic ω‾θ. One example for
the upwelling regions is the monthly mean for February. In
ω‾*, there are higher vertical velocities around the
equatorial minimum at 55 hPa than in ω‾θ. At
higher altitude at 12 hPa around the second equatorial minimum, there
are also high vertical velocities in ω‾*. Here, the
effect is most pronounced in the NH, where the kinematic upwelling is about
10 Paday-1 higher than the diabatic upwelling.
Another difference that is clearly visible in the annual mean is the wider
upwelling region of the diabatic ω‾θ below
700 K. This feature is present in all monthly means throughout the
year.
Vertical velocities ω‾θ from diabatic
heating rates in (Paday-1) and transformed Eulerian mean (TEM)
vertical velocity ω‾* in (Paday-1) from the
10-year EMAC climatology for the months January–June.
Vertical velocities ω‾θ from diabatic
heating rates in (Paday-1) and transformed Eulerian mean (TEM)
vertical velocity ω‾* in (Paday-1) from the
10-year EMAC climatology for the months July–December.
Acknowledgements
The authors thank P. Jöckel and N. Thomas for their support while working
with the models EMAC and CLaMS. We also acknowledge F. Schaps for support in
implementing the vertical velocity transformations. We thank S. Rast for
providing the tool to obtain the diabatic components from ECHAM6. We
acknowledge the Jülich Supercomputing Center (JSC) at Forschungszentrum
Jülich for providing computing time and support (project number JIEK71).
The article processing charges for this
open-access publication were covered by a Research
Centre of the Helmholtz Association. Edited by: M. Dameris
ReferencesAbalos, M., Legras, B., and Ploeger, F., and Randel, W. J.: Evaluating the
advective Brewer-Dobson circulation in three reanalyses for the period
1979–2012, J. Geophys. Res., 120, 7534–7554,
doi:10.1002/2015JD023182,
2015.
Andrews, D. G., Holton, J. R., and Leovy, C. B.: Middle Atmosphere Dynamics,
Academic Press, San Diego, 1987.Bechtold, P., Chaboureau, J., Beljaars, A., Betts, A., Kohler, M.,
Miller, M., and Redelsperger, J.: The simulation of the diurnal cycle of
convective precipitation over land in a global model, Q. J. Roy. Meteor.
Soc., 130, 3119–3137,
doi:10.1256/qj.03.103, 2004.
Brasseur, G. P., Orlando, J. J., and Tyndall, G. S. (Eds.): Atmospheric
Chemistry and Global Change, Oxford University Press, Oxford, 1999.Butchart, N., Scaife, A. A., Bourqui, M., de Grandpre, J., Hare, S. H. E.,
Kettleborough, J., Langematz, U., Manzini, E., Sassi, F., Shibata, K.,
Shindell, D., and Sigmond, M.: Simulations of anthropogenic change in the
strength of the Brewer–Dobson circulation, Clim. Dynam., 27, 727–741,
doi:10.1007/s00382-006-0162-4,
2006.
Carpenter, R. L., Droegemeier, K. K., Woodward, P. R., and Hane, C. E.:
Application of the Piecewise Parabolic Method (PPM) to meteorological
modeling, Mon. Weather Rev., 118, 586–612, 1990.
Danielsen, E. F.: Trajectories: isobaric, isentropic and
actual, J. Meteorol., 18, 479–486, 1961.
Dee, D. P., Uppala, S. M., Simmons, A. J., Berrisford, P.,
Poli, P., Kobayashi, S., Andrae, U., Balmaseda, M. A., Balsamo, G.,
Bauer, P., Bechtold, P., Beljaars, A. C. M., van de Berg, L., Bidlot, J.,
Bormann, N., Delsol, C., Dragani, R., Fuentes, M., Geer, A. J.,
Haimberger, L., Healy, S. B., Hersbach, H., Hólm, E. V., Isaksen, L.,
Kållberg, P., Köhler, M., Matricardi, M., McNally, A. P.,
Monge-Sanz, B. M., Morcrette, J. J., Park, B. K., Peubey, C., de Rosnay, P.,
Tavolato, C., Thépaut, J. N., and Vitart, F.: The ERA-Interim reanalysis:
configuration and performance of the data assimilation system, Q. J. Roy.
Meteor. Soc., 137, 553–597, 2011.Fueglistaler, S., Legras, B., Beljaars, A., Morcrette, J.-J., Simmons, A.,
Tompkins, A. M., and Uppala, S.: The diabatic heat budget of the upper
troposphere and lower/mid stratosphere in ECMWF reanalyses, Q. J. Roy.
Meteor. Soc., 135, 21–37,
doi:10.1002/qj.361, 2009.Garny, H., Birner, T., Bönisch, H., and Bunzel, F.: The effects of
mixing on age of air, J. Geophys. Res., 119, 7015–7034,
doi:10.1002/2013JD021417,
2014.Grooß, J.-U., Günther, G., Müller, R., Konopka, P., Bausch, S.,
Schlager, H., Voigt, C., Volk, C. M., and Toon, G. C.: Simulation of
denitrification and ozone loss for the Arctic winter 2002/2003, Atmos. Chem.
Phys., 5, 1437–1448,
doi:10.5194/acp-5-1437-2005,
2005.Hack, J. J.: Parameterization of moist convection in the National Center for
Atmospheric Research community climate model (CCM2), J. Geophys. Res., 99,
5551–5568,
doi:10.1029/93JD03478, 1994.
Hall, T. M. and Plumb, R. A.: Age as a diagnostic of stratospheric
transport, J. Geophys. Res., 99, 1059–1070, 1994.
Hines, C. O.: Doppler-spread parameterization of gravity-wave momentum
deposition in the middle atmosphere. Part 1: Basic formulation, J. Atmos.
Sol.-Terr. Phy., 59, 371–386, 1997.Hoppe, C. M.: A Lagrangian transport core for the simulation of stratospheric
trace species in a Chemistry Climate Model, PhD thesis, Bergische
Universität Wuppertal, Wuppertal, Germany, available at:
http://elpub.bib.uni-wuppertal.de/servlets/DocumentServlet?id=4210
(last access: 29 October 2015), 2014.Hoppe, C. M., Hoffmann, L., Konopka, P., Grooß, J.-U., Ploeger, F.,
Günther, G., Jöckel, P., and Müller, R.: The implementation of
the CLaMS Lagrangian transport core into the chemistry climate model EMAC
2.40.1: application on age of air and transport of long-lived trace species,
Geosci. Model Dev., 7, 2639–2651,
doi:10.5194/gmd-7-2639-2014,
2014.
Jöckel, P., von Kuhlmann, R., Lawrence, M., Steil, B., Brenninkmeijer, C.,
Crutzen, P., Rasch, P., and Eaton, B.: On a fundamental problem in
implementing flux-form advection schemes for tracer transport in
3-dimensional general circulation and chemistry transport models, Q. J. Roy.
Meteor. Soc., 127, 1035–1052, 2001.Jöckel, P., Tost, H., Pozzer, A., Brühl, C., Buchholz, J.,
Ganzeveld, L., Hoor, P., Kerkweg, A., Lawrence, M. G., Sander, R., Steil, B.,
Stiller, G., Tanarhte, M., Taraborrelli, D., van Aardenne, J., and
Lelieveld, J.: The atmospheric chemistry general circulation model
ECHAM5/MESSy1: consistent simulation of ozone from the surface to the
mesosphere, Atmos. Chem. Phys., 6, 5067–5104,
doi:10.5194/acp-6-5067-2006,
2006.Jöckel, P., Kerkweg, A., Pozzer, A., Sander, R., Tost, H., Riede, H.,
Baumgaertner, A., Gromov, S., and Kern, B.: Development cycle 2 of the
Modular Earth Submodel System (MESSy2), Geosci. Model Dev., 3, 717–752,
doi:10.5194/gmd-3-717-2010,
2010.
Kasahara, A.: Various vertical coordinate systems used for numerical weather
prediction, Mon. Weather Rev., 102, 509–522, 1974.Konopka, P., Steinhorst, H., Grooss, J., Günther, G., Müller, R.,
Elkins, J., Jost, H., Richard, E., Schmidt, U., Toon, G., and McKenna, D.:
Mixing and ozone loss in the 1999–2000 Arctic vortex: simulations with the
three-dimensional Chemical Lagrangian Model of the Stratosphere (CLaMS), J.
Geophys. Res., 109, D02315, 10.1029/2003JD003792, 2004.Lauritzen, P., Ullrich, P., and Nair, R.: Atmospheric transport schemes:
desirable properties and a semi-lagrangian view on finite-volume
discretizations, in: Numerical Techniques for Global Atmospheric Models,
edited by: Lauritzen, P., Jablonowski, C., Taylor, M., and Nair, R., Vol. 80
of Lecture Notes in Computational Science and Engineering, Springer, Berlin,
Heidelberg, 185–250,
doi:10.1007/978-3-642-11640-7_8,
2011.
Lin, S. and Rood, R.: Multidimensional flux-form semi-Lagrangian transport
schemes, Mon. Weather Rev., 124, 2046–2070, 1996.
Lin, S.-J.: A “vertically Lagrangian” finite-volume dynamical core for
global models, Mon. Weather Rev., 132, 2293–2307, 2004.Mahowald, N., Plumb, R., Rasch, P., del Corral, J., Sassi, F., and Heres, W.:
Stratospheric transport in a three-dimensional isentropic coordinate
model, J. Geophys. Res., 107, ACH3.1–ACH3.14, 10.1029/2001JD001313,
2002.McKenna, D. S., Grooß, J.-U., Günther, G., Konopka, P.,
Müller, R., Carver, G., and Sasano, Y.: A new Chemical Lagrangian Model
of the Stratosphere (CLaMS) 2. Formulation of chemistry scheme and
initialization, J. Geophys. Res., 107, ACH4.1–ACH4.14,
10.1029/2000JD000113, 2002a.McKenna, D. S., Konopka, P., Grooß, J.-U., Günther, G.,
Müller, R., Spang, R., Offermann, D., and Orsolini, Y.: A new Chemical
Lagrangian Model of the Stratosphere (CLaMS) 1. Formulation of advection and
mixing, J. Geophys. Res., 107, ACH15.1–ACH15.15, 10.1029/2000JD000114,
2002b.Nordeng, T.: Extended Versions of the Convective Parametrization Scheme at
ECMWF and Their Impact on the Mean and Transient Activity of the Model in the
Tropics, ECMWF technical memorandum, European Centre for Medium-Range Weather
Forecasts, available at: http://books.google.de/books?id=ozdmHQAACAAJ
(last access: 29 October 2015), 1994.Paul, J., Fortuin, F., and Kelder, H.: An ozone climatology based on
ozonesonde and satellite measurements, J. Geophys. Res., 103, 31709–31734,
doi:10.1029/1998JD200008,
1998.Ploeger, F., Konopka, P., Günther, G., Grooß, J.-U., and Müller, R.:
Impact of the vertical velocity scheme on modeling transport across the
tropical tropopause layer, Geophys. Res. Lett., 42, 1–8,
10.1002/2014GL062927, 2010.Ploeger, F., Fueglistaler, S., Grooß, J.-U., Günther, G.,
Konopka, P., Liu, Y.S., Müller, R., Ravegnani, F., Schiller, C.,
Ulanovski, A., and Riese, M.: Insight from ozone and water vapour on
transport in the tropical tropopause layer (TTL), Atmos. Chem. Phys., 11,
407–419,
doi:10.5194/acp-11-407-2011,
2011.Ploeger, F., Abalos, M., Birner, T., Konopka, P., Legras, B.,
Müller, R., and Riese, M.: Quantifying the effects of mixing and
residual circulation on trends of stratospheric mean age of air, J. Geophys.
Res., 42, 2047–2054,
doi:10.1002/2014GL062927,
2015.Pommrich, R., Müller, R., Grooß, J.-U., Konopka, P., Ploeger, F.,
Vogel, B., Tao, M., Hoppe, C. M., Günther, G., Spelten, N., Hoffmann, L.,
Pumphrey, H.-C., Viciani, S., D'Amato, F., Volk, C. M., Hoor, P.,
Schlager, H., and Riese, M.: Tropical troposphere to stratosphere transport
of carbon monoxide and long-lived trace species in the Chemical Lagrangian
Model of the Stratosphere (CLaMS), Geosci. Model Dev., 7, 2895–2916,
doi:10.5194/gmd-7-2895-2014,
2014.
Randel, W. J., Garcia, R. R., and Wu, F.: Dynamical balances and tropical
stratospheric upwelling, J. Atmos. Sci., 65, 3584–3595,
doi:10.1175/2008JAS2756.1,
2008.Roeckner, E., Bäuml, G., Bonaventura, L., Brokopf, R., Esch, M.,
Giorgetta, M., Hagemann, S., Kirchner, I., Kornblueh, L., Manzini, E.,
Rhodin, A., Schlese, U., Schulzweida, U., and Tompkins, A.: The atmospheric
general circulation model ECHAM5. PART I: Model description, Tech. Rep.
MPI-Report 349, Max Planck Institute for Meteorology, available at:
http://www.mpimet.mpg.de/fileadmin/publikationen/Reports/max_scirep_349.pdf
(last access: 29 October 2015), 2003.
Röckner, E., Brokopf, R., Esch, M., Giorgetta, M., Hagemann, S.,
Kornblueh, L., Manzini, E., Schlese, U., and Schulzweida, U.: Sensitivity of
simulated climate to horizontal and vertical resolution in the ECHAM5
atmosphere model, J. Climate, 19, 3771–3791, 2006.Schoeberl, M. R., Douglass, A. R., Zhu, Z. X., and Pawson, S.: A comparison
of the lower stratospheric age spectra derived from a general circulation
model and two data assimilation systems, J. Geophys. Res., 108, 4113,
10.1029/2002JD002652, 2003.Seviour, W. J. M., Butchart, N., and Hardiman, S. C.: The Brewer–Dobson
circulation inferred from ERA-Interim, Q. J. Roy. Meteor. Soc., 138,
878–888, doi:10.1002/qj.966, 2012.Stevens, B., Giorgetta, M., Esch, M., Mauritsen, T., Crueger, T., Rast, S.,
Salzmann, M., Schmidt, H., Bader, J., Block, K., Brokopf, R., Fast, I.,
Kinne, S., Kornblueh, L., Lohmann, U., Pincus, R., Reichler, T., and
Roeckner, E.: Atmospheric component of the MPI-M Earth System Model: ECHAM6,
Journal of Advances in Modeling Earth Systems, 5, 146–172,
doi:10.1002/jame.20015, 2013.
Tiedtke, M.: A comprehensive mass flux scheme for cumulaus parameterization
in large-scale models, Mon. Weather Rev., 117, 1779–1800, 1989.Tost, H., Jöckel, P., and Lelieveld, J.: Influence of different
convection parameterisations in a GCM, Atmos. Chem. Phys., 6, 5475–5493,
doi:10.5194/acp-6-5475-2006,
2006.Wohltmann, I. and Rex, M.: Improvement of vertical and residual velocities in
pressure or hybrid sigma-pressure coordinates in analysis data in the
stratosphere, Atmos. Chem. Phys., 8, 265–272,
doi:10.5194/acp-8-265-2008,
2008.Wright, J. S. and Fueglistaler, S.: Large differences in reanalyses of
diabatic heating in the tropical upper troposphere and lower stratosphere,
Atmos. Chem. Phys., 13, 9565–9576,
doi:10.5194/acp-13-9565-2013,
2013.
Zhang, G. and McFarlane, N.: Sensitivity of climate simulations to the
parameterization of cumulus convection in the Canadian climate center
general-circulation model, Atmos. Ocean, 33, 407–446, 1995.