ACPAtmospheric Chemistry and PhysicsACPAtmos. Chem. Phys.1680-7324Copernicus PublicationsGöttingen, Germany10.5194/acp-17-4657-2017Impact of typhoons on the composition of the upper troposphere within the Asian summer monsoon anticyclone: the SWOP campaign in Lhasa 2013LiDanlidan@mail.iap.ac.cnhttps://orcid.org/0000-0002-4812-5000VogelBärbelBianJianchunbjc@mail.iap.ac.cnhttps://orcid.org/0000-0001-9809-5834MüllerRolfhttps://orcid.org/0000-0002-5024-9977PanLaura L.GüntherGebhardhttps://orcid.org/0000-0003-4111-6221BaiZhixuanLiQianZhangJinqiangFanQiujunVömelHolgerhttps://orcid.org/0000-0003-1223-3429Key Laboratory of Middle Atmosphere and Global Environment Observation (LAGEO), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, ChinaInstitute of Energy and Climate Research, Stratosphere (IEK-7), Forschungszentrum Jülich, Jülich, GermanyCollege of Earth Science, University of Chinese Academy of Sciences, Beijing, ChinaAtmospheric Chemistry Observations & Modeling, National Center for Atmospheric Research, Boulder, CO, USAEarth Observing Laboratory, National Center for Atmospheric Research, Boulder, CO, USADan Li (lidan@mail.iap.ac.cn) and Jianchun Bian (bjc@mail.iap.ac.cn)10April20171774657467230September201625October201623February201712March2017This 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/17/4657/2017/acp-17-4657-2017.htmlThe full text article is available as a PDF file from https://acp.copernicus.org/articles/17/4657/2017/acp-17-4657-2017.pdf
In the frame of the SWOP (sounding water vapour, ozone, and particle)
campaign during the Asian summer monsoon (ASM), ozone and water vapour
profiles were measured by balloon-borne sensors launched from Lhasa
(29.66∘ N, 91.14∘ E, elevation 3650 m), China, in August
2013. In total, 24 soundings were launched, nearly half of which show strong
variations in the relationship between ozone and water vapour in the
tracer–tracer correlation in the upper troposphere and lower stratosphere
(UTLS). For each sounding, 20-day backward trajectories were calculated using
the trajectory module of the Chemical Lagrangian Model of the Stratosphere
(CLaMS) to analyse these variations. The trajectory calculations demonstrate
that three tropical cyclones (tropical storm Jebi, typhoons Utor and Trami),
which occurred over the western Pacific Ocean during August 2013, had a
considerable impact on the vertical distribution of ozone and water vapour by
uplifting marine air masses to altitudes of the ASM anticyclone. Air parcels
subsequently arrived at the observation site via two primary pathways:
firstly via direct horizontal transport from the location of the typhoon to
the station within approximately 3 days, and secondly via transport
following the clockwise wind flow of the ASM within a timescale of 1 week.
Furthermore, the interplay between the spatial position of the ASM
anticyclone and tropical cyclones plays a key role in controlling the
transport pathways of air parcels from the boundary layer of the western
Pacific to Lhasa in horizontal and vertical transport. Moreover, the
statistical analysis shows that the strongest impact by typhoons is found at
altitudes between 14.5 and 17 km (365–375 K). Low ozone values
(50–80 ppbv) were observed between 370 and 380 K due to the strong
vertical transport within tropical cyclones.
Introduction
The Asian summer monsoon (ASM) anticyclone is one of the largest upper-level
circulation systems that spans from Southeast Asia to the Middle East in the
upper troposphere-lower stratosphere (UTLS) during the boreal summer
. The ASM is considered to be coupled with persistent
monsoonal convection over the South Asian region during the summer season
. The longitudinal distribution of the core of
the ASM anticyclone has two preferred modes, referred to as the Iranian mode
and the Tibetan mode . This bimodality has an
impact on the distribution of atmospheric trace species (such as water vapour
and ozone) and dynamic parameters in the UTLS region . The
total column ozone (TCO) over the Tibetan Plateau in the boreal summer is
lower than that of other regions at the same latitude . This
phenomenon is termed as the “summertime ozone valley”. The transport
associated with the ASM circulation is one of the most critical causes of the
summertime ozone valley over the Tibetan Plateau .
The ASM is recognized as an important transport pathway for boundary layer
air enriched in greenhouse gases, water vapour, or pollutants (e.g. hydrogen
cyanide (HCN) produced by biomass burning, carbon monoxide, aerosol) to
enter the stratosphere
e.g.. According
to trajectory simulations, air within the ASM anticyclone is impacted by
surface sources from various regions: the western Pacific Ocean, India and
Southeast Asia, Eastern China, the Tibetan Plateau, and the Indian Ocean
. Using trajectory
calculations during the summers of 2001–2009, showed that
38 % of the air mass at tropopause height within the ASM region is from
the western Pacific region and South China Sea.
demonstrated that 10 % of the air mass in the anticyclone at 100 hPa
originated from the western Pacific in August 2001. Using artificial emission
tracers in CLaMS (the Chemical Lagrangian Model of the Stratosphere) in
summer 2012, found a strong temporal variability in
contributions from Southeast Asia to the composition of the ASM anticyclone
during the monsoon season at 380 K. The major transport processes for
tropospheric tracers transporting from boundary layer sources to the upper
troposphere and lower stratosphere include both deep convection with rapid
vertical transport and large-scale slow upward circulation within the ASM
anticyclone . An additional transport
pathway from the boundary layer to the edge region of the ASM is strong
uplift in typhoons and, subsequently, entrainment into the circulation of the
anticyclone .
Tropical cyclones vary in the horizontal scale over a wide range from 100 to
2000 km, characterized by spiral rain-bands, which consist of bands of
cumulus convection clouds . These bands of clouds are
often accompanied and sometimes dominated by strong updrafts, whereas
downdrafts occur concomitantly between these convective clouds. The vertical
typhoon circulation with strong uplift can lift marine boundary layer air
masses into the UTLS region . The tropical
Pacific and western Atlantic are situated far away from anthropogenic
emissions and biomass burning sources, and are thus characterized by low
ozone values in the lower troposphere .
Therefore, low ozone concentrations are sometimes measured in the upper
troposphere within typhoons or hurricanes . Using
balloon-borne ozone data over Socorro (North America),
show how a hurricane uplifts eastern–central tropical
Pacific boundary air with extremely low ozone to the upper troposphere.
Meanwhile, the downdraft in typhoons can transport ozone-rich air from the
lower stratosphere down to the troposphere and even to the
surface . Thus, tropical cyclones exert critical impact on
air masses and energy transport between the surface and the UTLS region
.
In several model studies, contributions of air masses originating from the
western Pacific are found within the ASM anticyclone region
e.g.
during summer. Furthermore, in the western Pacific belt, tropical cyclones
reach peak activity in late summer . Several previous
studies have suggested an impact of deep convection by tropical cyclones, in
particular typhoons, on the chemical composition of the ASM anticyclone
e.g.. In spite of the
many satellite measurements and model simulations, the transport process of
air masses from the planetary boundary layer of the western Pacific Ocean to
the ASM anticyclone associated with typhoons is still unclear and requires
further investigations. In situ measurements of the atmospheric chemical
compositions over the Tibetan Plateau are sparse
. In this study, balloon measurements with high
vertical resolution from Lhasa in August 2013 provide highly accurate water
vapour and ozone profiles from the surface to the lower stratosphere.
Combining these in situ measurements with trajectory calculations performed
using the CLaMS model and references
therein is an ideal method for analysing the
source regions and transport pathways of air masses affected by tropical
cyclones.
The goals of this investigation are to both identify transport pathways from
air masses uplifted by tropical cyclones into the ASM anticyclone and
quantify their impact on ozone observed in the upper troposphere over the
Tibetan Plateau in August 2013. This paper is organized as follows:
Sect. describes the balloon sonde data and the trajectory
calculation with CLaMS. In Sect. , we present the tropical
cyclones that might have affected the composition in Lhasa during summer
2013. In Sect. , we focus on model results as well as the
spatial position interplay between ASM and cyclones. In the final section, we
summarize the results and present our conclusions.
Data and model descriptionData
To investigate the spatial variability of the UTLS ozone concentration and
water vapour in the ASM anticyclone, the SWOP (sounding water vapour, ozone,
and particle) campaign was conducted by the Institute of Atmospheric Physics,
Chinese Academy of Sciences, during the summer monsoon period. Balloon sondes
were launched in Lhasa (29.66∘ N, 91.14∘ E, 3650 m above
sea level (a.s.l.)), China, in August 2013. Lhasa is located on the Tibetan
Plateau, one of the source regions of air masses found within the ASM
anticyclone. More detailed information of the Lhasa site is provided by
in Fig. 1. A total of 24 soundings were launched at a
rate of once per day around 22:30 BST (Beijing Standard Time, UTC + 8)
from 4 to 27 August 2013. The serial numbers of balloon sondes, dates, and
times for each balloon are listed in Table .
Flight statics for balloon launches during the August 2013 SWOP
campaign in Lhasa.
The balloon-borne payloads consist of a cryogenic frost point hygrometer
(CFH) , an electrochemical concentration cell (ECC)
ozonesonde, and an iMet radiosonde to measure profiles of water vapour,
ozone, and routine meteorological variables (pressure, temperature, relative
humidity, and winds). On average, a balloon ascent lasts for
∼ 75 min from the surface to about 30 km altitude before bursting.
The measurement uncertainty of CFH is less than 9 % in the tropopause
region , and the ozone uncertainty estimated by
is better than 5–10 %. The ECC sensor response time is
about 22 s in the troposphere and the balloon ascent
rate is ∼ 4–6 m s-1. As a result, the ozone and water vapour
mixing ratios are provided with a 100 m vertical resolution from the surface
through 50 hPa to attenuate the instrument response time effect
.
A scatter plot of the water vapour and ozone of all balloon flights in
August 2013 is shown in Fig. . A double-logarithmic
scale is used to highlight the correlation between water vapour and ozone in
the UTLS region. The two tracers typically have an L-shaped correlation in
tracer–tracer space , but some profiles
reveal relatively low ozone or low water vapour in the UTLS region (see
profiles that are marked in colour in Fig. ) compared to
all other profiles measured in Lhasa during August 2013.
H2O–O3 correlations for balloon profiles measured over Lhasa
in August 2013 (grey colour). The profiles measured on 11–12 August were
impacted by tropical storm Jebi and measurements on 19 and 23–25 August were
impacted by typhoon Utor or Trami. The layers of three profiles influenced by
tropical cyclones are highlighted (inset).
The observation on 11 August 2013 (Fig. , in red) shows
a distribution, with low ozone and low water vapour in the corner of the
“L” (corresponding to the UTLS region), but with very high ozone in the
troposphere, where water vapour has a concentration between 100 and
500 ppmv. The transport processes leading to these conditions will be
studied in section . On the next day, a profile (marked in
green) demonstrates particularly low water vapour in the troposphere. Another
three profiles also show low water vapour and low ozone structure in the UTLS
region during the period of 23–25 August. High ozone (> 100 ppbv) was
observed when water vapour mixing ratios were greater than 30 ppmv on
19 August. The extremely low ozone (∼ 50 ppbv) and low water vapour
(∼ 5 ppmv) are displayed in the corner of the L from 23 to
25 August 2013. A similar correlation has also been reported by
based on measurements in Kunming (25.01∘ N,
102.65∘ E, 1889 m a.s.l.), China, in 2009.
show that low ozone near the tropopause is caused by rapid ascent in oceanic
deep convective systems associated with a tropical typhoon. In the same way,
several profiles measured in Lhasa in 2013 are impacted by different tropical
cyclones. The regions of three profiles impacted by cyclones, which were
measured on 11, 19, and 24 August 2013, are highlighted in
Fig. (inset) and will be discussed in more detail in
Sect. .
Model
In order to investigate the distributions with low ozone and low water vapour
in the UTLS region, the trajectory module of the CLaMS model and
references therein was used to calculate 20-day
backward trajectories along each balloon's ascent flight path in Lhasa in
2013. The CLaMS model is particularly well-suited for the simulation of
tracer transport in the vicinity of strong transport barriers and the
associated tracer gradients such as the polar vortex
e.g., the extratropical tropopause
e.g., and the Asian monsoon anticyclone
e.g.. CLaMS was applied to analyse
aircraft and balloon measurements with a focus on stratospheric chemistry
(e.g. ozone loss processes) e.g. and the transport of
trace gases (e.g. water vapour and ozone) in the UTLS
e.g.. The model was driven by dynamic fields from the
European Centre for Medium-range Weather Forecasts (ECMWF) re-analysis
interim (ERA-Interim) . The input data are recorded at 6 h
intervals on a regular grid with 1∘× 1∘ in
latitude–longitude on hybrid levels (60 levels from 1013.25 to 0.1 hPa). A
hybrid vertical coordinate ζ is employed in the CLaMS model. The
isentropic coordinate θ is used when the pressure is less than
300 hPa, and a pressure-based orography-following coordinate is used when
the pressure is higher than 300 hPa .
Classification of tropical cyclones Jebi, Utor, and Trami in
2013.
NameDurationLowest pressureMaximum sustained windSSHWSJebi28 Jul–3 Aug985 hPa95 km h-1Tropical stormUtor8–18 Aug925 hPa195 km h-14Trami16–24 Aug965 hPa110 km h-11
To further investigate the boundary sources of air parcels near the
tropopause layer in Lhasa, parcels were selected according to the following
criteria: parcels that reach the lower troposphere (LT) within 20-day
backward trajectories are referred to as “target air parcels”. Here, the
top of the model boundary layer is defined as ζ< 190 K
(approximately 3.0 km above the surface). ζ as a terrain-following
coordinate is universally applicable for keeping the vertical spacing between
the Earth's surface and the top of the LT constant. On the basis of this
criterion, parcels from the upper troposphere and lower stratosphere within
20-day backward trajectories are eliminated. As a result, we focus solely on
the air parcels that reach to the top of the model boundary layer and are
uplifted to the location of the measurement.
Tropical cyclones in August 2013
After analysing the 20-day backward trajectories from the output of CLaMS, we
found that three tropical cyclones (named Trami, Jebi, and Utor), which
occurred over the western Pacific, influence the composition in middle–upper
troposphere at the Lhasa site. Table shows the name of the
cyclones, their duration, lowest pressure, maximum sustained wind (10 min
mean), and the Saffir–Simpson hurricane wind scale (SSHWS) index. Typhoon
Utor is the strongest of the three typhoons with lowest pressure of 925 hPa,
maximum sustained wind of 195 km h-1, and an SSHWS index of 4, the highest of the three
tropical cyclones (for more details see
website:
http://agora.ex.nii.ac.jp/digital-typhoon/year/wnp/2013.html.en and
http://www.nrlmry.navy.mil/tcdat/tc13/WPAC/.
).
Typhoon Trami developed east of Taiwan on 16 August 2013. During the next 2 days it moved towards the southeast, continued to gain in strength, and was
upgraded to a tropical storm. Trami turned northward on 19 August and then
turned northwestward on 20 August. After moving west-northwestward over the
East China Sea, Trami hit Fujian Province, China, on 21 August. Over the next
couple of days, it continued to pass through Jiangxi and Hunan, China. Finally, Trami dissipated over Guangxi on 24 August (see green dots
in Fig. a; the blue points will be discussed in
Sect. ).
Pathways of tropical cyclones (a) Trami,
(b) Jebi, and (c) Utor are marked as green dots for every
6 h. The number printed inside the large green dots indicates the day in
August 2013, except 29 and 31 in (b), which refer to 29 and 31 July.
The blue points denote the average geographical position where air parcels
experienced strong uplift within tropical cyclones. The red star marks the
location of Lhasa.
On 28 July 2013, tropical depression Jebi formed near the southern coast of
Luzon Island. As it moved northwestward, it was observed crossing the
Philippines and reached the South China Sea on 30 July before it continued to
move northwestward. After crossing the northern part of Hainan Island and the
Gulf of Tonkin, Jebi made landfall over northern Vietnam on 3 August and
dissipated several hours later (track and date are marked in
Fig. b).
Typhoon Utor formed northwest of the Yap Island on 8 August 2013. As this
system moved westward, it developed rapidly and was upgraded to typhoon
intensity on 10 August. Turning west-northwestward on 11 August, Utor reached
its peak intensity (SSHWS, category 4). After hitting Luzon Island, it
maintained its typhoon intensity over the South China Sea. The system then
tracked northward and Utor made landfall over Yangjiang in Guangdong, China,
on 14 August. On the next day, Utor weakened into a tropical depression. However,
the remnants began tracking very slowly in the Guangxi region until the
tropical depression finally dissipated on 18 August (see
Fig. c).
According to 20-day backward-trajectory calculations, 13 profiles were
impacted by these three western Pacific tropical cyclones (marked in the last
column of Table ). From 11 to 13 August, tropical storm
Jebi transported air parcels to the Lhasa site. Typhoon Utor had a long-term
impact on the profiles during the period of 17–26 August. The last four
profiles were impacted by both typhoon Utor and typhoon Trami. Three profiles
highlighted in bold in Table (11, 19, and 24 August) were
influenced by different tropical cyclones and will be discussed in detail in
Sect. .
Results
To obtain further insight into the impact of tropical cyclones on ozone and
water vapour in the upper troposphere in Lhasa, we analyse three ozone and
water vapour profiles (bold in Table ) as a case study. The
results shown below are based on ozone and water vapour profiles observed at
the Lhasa site on 11, 19, and 24 August associated with 20-day backward
trajectories from the CLaMS model. In addition, the meteorological conditions
that caused the transport of air parcels from the western Pacific to Lhasa
are analysed.
The 20-day backward trajectories started along measured balloon profiles
of target parcels on 24 (a, c), 11 (d, f), and
19 (g, i) August 2013. Backward trajectories influenced by tropical
cyclones Trami, Jebi, and Utor are shown colour-coded by temperature (left).
The vertical profiles of ozone (blue line), water vapour (black line), and
the mean of ozone profiles in August 2013 (grey line) are also shown
(middle). The geographical position (latitude, longitude, and altitude) of
the 20-day backward trajectories is given (right) colour-coded by days
observed from measurement. The vertical line marks the location of the Lhasa
site. The grey lines in the maps show the longitude–latitude projection of
the trajectories.
Analyses of three selected casesCase 1 (Trami)
Figure a–c show the CLaMS backward trajectories and measured
profiles of ozone and water vapour influenced by typhoon Trami. The mean
ozone profile is obtained by averaging individual profiles over Lhasa in
August 2013 (grey line in Fig. b). At 14:13 UTC on
24 August, very low ozone mixing ratios of about 50 ppbv (lower than the
average of ozone mixing ratios) and low water vapour mixing ratios of about
7 ppmv (lower than other water vapour values in Fig. )
were measured just below the tropopause (the World Meteorological
Organization (WMO) tropopause altitude is 17.6 km) in a 14–16.5 km layer.
The same format as Fig. (left), but potential
vorticity (1 PVU = 106 K m2 kg-1 s-1) is shown along
20-day backward trajectories for observations impacted by (a) Trami,
(b) Jebi, and (c) Utor.
In Fig. a and c, 20-day backward trajectories initialized in Lhasa on 24 August
show that air parcels with low ozone
concentration originated from the boundary layer of the western Pacific
Ocean. Most of the air parcels were lifted up to ∼ 17 km through the
strong upward airflow associated with typhoon Trami. When these parcels
arrived at the tropopause region, they encountered the cold upper troposphere
in the western Pacific Ocean. The minimum temperature of each parcel ranged
from -82.3 to -72.7∘ C (Fig. a). Using
Eq. (7) of , we calculate the vapour pressure over ice. The
water vapour mixing ratios are obtained by using vapour pressure divided by
air pressure, with a range of 3.1 to 12.4 ppmv for the above-mentioned
temperature range. This value range is in good agreement with the water
vapour measured in this layer, indicating that the air parcels were
dehydrated when they passed through the cold upper troposphere of the western
Pacific. Air parcels originated from the marine boundary layer, moving
rapidly upward where the process of strong uplift occurred from 18 to
21 August (Fig. a). Furthermore, the value of potential
vorticity (PV) is lower than 2 PVU during the period of strong upward
transport, indicating rapid uplift of boundary layer air masses to the upper
troposphere (Fig. a). Indeed, PV is a good tracer for the
stratosphere, however, it is not well conserved in the troposphere.
Nevertheless, PV values in the upper troposphere are a good indicator for
stratospheric or tropospheric origin of air masses
e.g..
Air parcels with low ozone travelled 3000 km horizontally within 3 days
from the top of typhoon Trami to the Lhasa site, with PV increasing slowly.
This indicates the rapid and direct influence of typhoon-induced transport on
ozone mixing ratios and water vapour in the upper troposphere over Lhasa
within a short timescale. Our findings are in accordance with a study by
showing that low ozone mixing ratios in altitudes higher than
200 hPa were also observed right above the track of typhoon Haitang in 2005
over the western Pacific using Aura's Ozone Monitoring Instrument data. The
reason for this is the strong upward propagation of air masses associated
with deep convection in typhoons. also demonstrate
that meteorological conditions associated with a tropical cyclone (Henriette)
have a strong influence on ozone mixing ratios in the upper troposphere over
timescales of 3–5 days.
The geopotential height at 100 hPa pressure level (blue contour
lines, > 16.72 km) and sea-level air pressure (shade, hPa) of Trami at
(a) 06:00 UTC 20 August, (b) 18:00 UTC 21 August, and
(c) 00:00 UTC 23 August. The asterisks, colour-coded by potential
temperature, mark the geographical positions of target parcels. The red star
marks the location of Lhasa.
Case 2 (Jebi)
Shown in Fig. d are 20-day backward trajectories of target parcels influenced by tropical storm
Jebi on 11 August 2013. Most air parcels
are uplifted from the LT and the planetary boundary layer to altitudes just
below the tropopause within a timescale of more than 1 week. However,
backward trajectories of three air parcels show a very rapid uplift during
the period of 1–3 August. These air parcels reach a maximum altitude of
approximately 16 km. The parcels also pass through a region of very low
temperatures (-75∘ C) in the upper troposphere above the tropical
western Pacific where they dehydrate. These air parcels are very dry, with
water vapour mixing ratios of ∼ 8 ppmv. The PV values associated with
these air masses are lower than 2 PVU (1 PVU = 106 K m2 kg-1 s-1) during ascent. After the parcels arrived at the maximum
altitude, the parcel PV increased, especially for the parcels located at a
higher altitude, with PV values greater than 2 PVU (Fig. b).
On 11 August 2013, the parcels reached an altitude of 12–15 km (which is
much lower than the WMO tropopause altitude of 17.25 km) over Lhasa, with a
slow downwelling in altitude levels within approximately 1 week. Low ozone
and low water vapour are observed in this layer (Fig. e).
These measurements indicate that tropical storm Jebi also lofted air with low
ozone from the LT of the tropical Pacific to Lhasa. A very high ozone peak
was also observed in the 10.5–12 km layer, with an ozone enhancement at
100 ppbv. The reason for this observation is that the air originating from
the lower stratosphere with high ozone concentration intruded into this layer
(not shown here).
The three-dimensional transport pathways of air parcels are displayed in
Fig. f. Air parcels are lifted from the western Pacific to
near the tropopause layer through strong vertical air flow associated with
the tropical storm Jebi. The parcels are then transported around the ASM
anticyclone within a timescale of 1 week. showed in a
case study that boundary layer air masses originating in Southeast Asia were
rapidly uplifted within typhoon Bolaven. For the case study shown here, the
vertical transport mechanism of typhoon Jebi is similar to that found in
typhoon Bolaven . All ozone and water vapour profiles
observed on 12 and 13 August 2013 are impacted by tropical storm Jebi
(Table ). The backward trajectories are similar to those
for 11 August (trajectories not shown here).
The same format as Fig. , but for Jebi. Here the
geopotential height is shown at 150 hPa pressure level.
Case 3 (Utor)
In contrast to case 1 and case 2, the vertical profiles of ozone and water
vapour show a remarkable laminar structure in the middle and upper
troposphere on 19 August (Fig. h). Ozone mixing ratios
display a high value (low value) between 9.3 and 10.2 km (10.2–11.2 km).
In contrast, the water vapour mixing ratio here exhibits low local value
(high value). Above 11 km, the ozone values are much larger than the mean
ozone profile, except in a layer of 13.2–14.5 km. Many factors such as
convection , gravity or Rossby wave ,
and stratospheric intrusions e.g. can cause the
laminated vertical structure of ozone in the middle–upper troposphere and
lower stratosphere.
The same format as Fig. , but for typhoon Utor. In
addition, PV isolines (> 2 PVU, solid black lines) are shown in
Fig. b.
The CLaMS trajectory calculations show that two clusters of air parcels
originating from the surface can be traced under the influence of typhoon
Utor (Fig. g and i). Target parcels at higher altitude in the
upper troposphere originate from the western Pacific Ocean and are first
uplifted to an altitude of 14 km within 2 days. The maximum altitudes of
target parcels under the uplift effect of typhoon Utor are lower compared to
those of cases Trami and Jebi. Secondly, air parcels reach the maximum
altitude at 18:00 UTC on 12 August after slow upwelling. Subsequently, these
target air parcels were transported quasi-horizontally and arrived at the
Lhasa observatory on 19 August. When the air parcels reached the highest
altitude, the PV increased strongly within about 3 days
(Fig. c). Both high PV values and high concentrations of
ozone of the air parcels at an altitude of 15 km (see
Fig. h) indicate a stratospheric origin of theses air parcels
(for more details, see Fig. b and discussion in
Sect. ).
Target parcels at lower altitude are transported from the lower troposphere
to the middle troposphere by convective uplift associated with the landfall
of Utor (Fig. g and i), causing the low ozone and high water
vapour observed in the middle troposphere. Our findings show that typhoon
Utor pumped air parcels from the boundary layer to the upper and middle
troposphere both before and after landfall.
Interplay between ASM and tropical cyclones
To better understand the interplay between the ASM anticyclone and typhoons,
the meteorological conditions are analysed in detail for the cases considered
here. Figures – show the geopotential
height of the ASM anticyclone at 100 hPa (or 150 hPa) pressure level and the
sea-level air pressure of the three tropical cyclones. The ASM anticyclone is
characterized by a pronounced east–west oscillation of the location of the
core of the ASM anticyclone: the Tibetan mode and the Iranian mode (see
Fig. ). The bimodality in the location of the anticyclone
has been found in previous earlier studies at 100 hPa for daily data
, for pentad (5-day) mean data , and for
monthly mean data .
At 06:00 UTC on 20 August 2013, typhoon Trami was located right below the
southeastern edge of ASM anticyclone circulation, with most of the target
parcels located inside the typhoon characterized by low potential temperature
(∼ 330 K) (Fig. a). The
parcels reached altitudes of the ASM (∼ 360 K) 36 h later due to the
strong upward propagation of deep convection in typhoon Trami
(Fig. b). This strong uplift can be seen clearly in
Fig. a. After the parcels entered the ASM, they travelled
along the easterly wind flow on the south side of the ASM anticyclone. The
interplay between the spatial position of the ASM anticyclone's circulation
and the typhoon creates conditions that can rapidly pump air parcels with low
ozone from the marine boundary layer to an altitude of 16 km. The parcels
are then dehydrated and transported to Lhasa on a short timescale. It is for
the precise reason that the entire process (uplifting and horizontal
transport) occurs on a short timescale of about 1 week that the low ozone
mixing ratios and low water vapour can be detected at the Lhasa site.
Outgoing long-wave radiation from AIRS satellite on 21, 3, and
12 August. The asterisks mark the locations of target air parcels at the time
of the AIRS measurements.
The relative frequency distribution of the target air masses
originating from the boundary layer with the influence of typhoons (red) and
without the influence of typhoons (blue) versus (a) altitude and
(b) potential temperature in August 2013.
Focusing on the Jebi case, the ASM circulation differs from the Trami case.
It has two centres, with the main core located over the Iranian Plateau and
the weak centre located over the western Pacific. The Lhasa site is located
on the eastern side of the primary centre of the ASM anticyclone
(Fig. ). Parcels from the marine boundary layer are lifted
by updraft associated with tropical storm Jebi, with potential temperature
increasing slowly, and are then entrained into the southeast edge of the ASM
anticyclone (Fig. a and b). The westward flow of the ASM
moves the parcels from right above the cyclone's track
(∼ 110∘ E) to the western edge of the ASM
(∼ 20∘ E). They subsequently move clockwise around the ASM
before they arrive at the Lhasa site (Fig. c–e). The
potential temperature of the air parcels increases to 370 K.
show a similar transport pathway around the outer edge of
the ASM anticyclone.
At 18:00 UTC on 12 August, the core of the ASM was located over the Iranian
Plateau; the position of typhoon Utor was disconnected from the position of
the ASM (Fig. a). The core of the ASM was
divided into two centres 3 days later, with the primary core located over the Tibetan
Plateau. Utor made landfall next to the southeast edge of the main core of
the ASM. At the same time, high-latitude air with high PV intruded
equatorward between the southeast edge of the ASM and the northwest edge at
the top of typhoon Utor, forming a thin filament at the east side of the
Tibetan Plateau (Fig. b). The strong horizontal wind shear
caused the mixing processes that occurred between air masses from the UTLS
region at high latitude with high PV and high ozone concentrations and air
masses from the lower troposphere of the western Pacific with low ozone
mixing ratios. As a result, we observed ozone concentrations in laminar
structures in the upper troposphere at the Lhasa site (see
Fig. h). A detailed analysis of mixing processes affecting
ozone and water vapour is beyond the scope of this study. However, in-mixing
of air mass from the stratosphere influences the structure of ozone profiles
observed at the Lhasa site. From 12:00 UTC on 18 August, the parcels were
transported around the low-pressure system, which was located at around
110∘ E, 28∘ N (see Fig. c), before slowly
moving to Lhasa. The spatial interplay between the position of the primary
core of the anticyclone and typhoons is a key factor influencing the
transport pathways of air parcels from the top of typhoons to the Lhasa site.
The outgoing long-wave radiation (OLR) of AIRS (atmospheric infrared sounder)
version 6.0 Level-2 is shown in Fig. with the
locations of target air parcels on 21, 3, and 12 August. Note that low values
of OLR indicate the deep convective. As Fig. a shows,
the spiral bands with low OLR values indicate the cloud band associated with
typhoon Trami. For typhoon Trami and storm Jebi, the strong uplift process of
air parcels occurred over the convective zone (Fig. a
and b). However, for typhoon Utor, the locations of strong uplift of a few parcels
are far away from the cyclone (Fig. c). For these air
parcels, uplift occurs at a different point in time than 12 August 2013 (see
target parcels at lower altitude in Fig. g).
Impact of tropical cyclone on UT ozone
The average geographical locations for which strong uplift
(> 9 K day-1) of target air parcels occurred under the influence of
tropical cyclones are shown in Fig. . The target air
parcels under the influence of typhoon Trami analysed in our case study
experienced strong upward transport over the Pacific Ocean. Rare air target
parcels were detected after Trami made landfall. The reason for this was
because no further balloon measurements were available after the end of the
campaign on 27 August 2013 (Fig. a). The geographical
location of the strong uplift of parcels moves along the track of tropical
storm Jebi over the region from the western Pacific to South China
(Fig. b). Furthermore, typhoon Utor exerts a major
influence on the uplifting of most target parcels after its landfall. This is
caused by the long lifetime of Utor after landfall. In contrast, in Lhasa only a few
target parcels are detected that experienced strong uplift before
Utor's landfall (Fig. c).
Figure shows the relative frequency distribution of target
air parcels originating from the LT; each colour bar represents the results
with or without the influence of tropical cyclones. The relative frequency is
calculated as the fraction, which is defined as the number of target air
parcels within each layer divided by the total number of all parcels of each
layer sampled in Lhasa (altitude range: 7–19 km (330–390 K), thickness of
each layer is 500 m (2.5 K)). The probability distribution of the target
parcels influenced by typhoons (red colour bars) shows two peaks: the first
peak at around 15.5 km (365 K) and a second peak at around 10 km (350 K). In
contrast, the target parcels uplifted without the impact of typhoons (e.g. by
convection; blue colour bars) show a broader distribution at altitudes of
∼ 7–13 km (340–360 K). It is clear that only the target parcels
considerably impacted by typhoons show a clear peak structure in the layer of
14.5–17 km (365–375 K). This finding indicates that strong vertical
transport within typhoons over the ocean can pump air parcels from the
boundary layer to a higher altitude than convection over land.
In Fig. , the frequency distributions of all ozone profiles
observed in August 2013 are shown at four isentropic layers in order to
demonstrate that ozone values near the tropopause could be influenced by
typhoons. The relative frequency is calculated as the fraction of the number
of air parcels with each bin of ozone value (10 ppbv in the layers of
360–370 K and 370–380 K, 5 ppbv in the layers of 340–350 K and 350–360 K)
divided by the total parcels of each layer. Ozone with or without the
influence of tropical cyclones (ozone–typhoons or ozone–no typhoons) is
identified as the parcels from Fig. b. The highest layer,
between 370 and 380 K potential temperature, shows three ozone maxima, with
the major ozone maximum of 0.2 between 120 and 140 ppbv (in black). The
maximum with low ozone value (50–80 ppbv, in red) is associated with strong
vertical transport, with the significant effects of tropical cyclones over
potential temperature levels of ∼ 370–380 K (Fig. a).
Distributions of ozone in Lhasa shift toward lower concentrations in the
layers of 360–370 K and 340–350 K (Fig. b and d). However,
the ozone concentration in the layer of 350–360 K shows a wide distribution
with ozone of 65–110 ppbv. This layer is influenced by convective outflow
of the ASM region and is also a region penetrated
by stratospheric intrusions . As a result, air masses
with both low and high ozone concentration are transported to the layer of
350–360 K, resulting in the strong variability observed.
The relative frequency distribution of all ozone profiles observed
in August 2013 (ozone–obs, in black) and ozone with (ozone–typhoons, in
red) or without (ozone–no typhoons, in blue) the influence of tropical
cyclones with respect to potential temperature layers of
(a) 370–380 K, (b) 360–370 K, (c) 350–360 K,
and (d) 340–350 K.
Summary and conclusions
High-resolution ozone and water vapour profiles over Lhasa, China, were
measured once per day over the period from 4 to 27 August 2013 in the frame
of the SWOP campaign. Half of them show a strong variability in the
correlation between ozone and water vapour mixing ratios in the upper
troposphere region. These relationships were investigated using CLaMS
trajectory calculations driven by ERA-Interim reanalysis data. We find that
tropical storm Jebi and typhoons Utor and Trami, which occurred over the
western Pacific during this period, had a strong impact on the vertical
structure of ozone and water vapour profiles measured in Lhasa. Tropical
cyclones lift air masses from the lower troposphere and the planetary
boundary layer up to altitudes close to the tropopause region. Air parcels
uplifted by tropical cyclones can reach Lhasa via two different horizontal
long-range transport pathways: (a) direct horizontal transport, where the parcels
travelled directly from the top of the typhoon to the Lhasa site within about
3 days, and (b) transport around the ASM anticyclone, where the parcels are
transported around the ASM anticyclone within a timescale of more than 1 week. The main updraught of air parcels occurred over the western Pacific, then
subsequently these air parcels were horizontally transported to the Lhasa
site. Additional analysis of vertical velocities over Lhasa in August 2013
shows that vertical velocities over Lhasa are much lower than in tropical
cyclones (not shown here).
Transport pathways of air parcels depend strongly on the relative spatial
position of the main core of the ASM anticyclone and the tropical cyclones. A
relatively close position between the ASM and typhoon Trami led to the
parcels arriving at the Lhasa site in a short period of time, passing through
the very cold upper troposphere over the western Pacific Ocean. As a result,
low ozone and low water vapour structures are clearly observed at the Lhasa
site. The timing as well as the spatial co-location between the ASM
anticyclone and the tropical cyclone determine whether target air parcels
from the boundary layer can reach the upper troposphere over Lhasa.
Tropical cyclones have different impacts on the vertical transport of air
parcels from the boundary layer up to the upper troposphere. We found that
typhoon Trami had an important effect on the strong uplift of air parcels
measured over Lhasa during the period of time when Trami was located over the
Pacific Ocean. Tropical storm Jebi was able to pump air masses from the lower
troposphere to near the tropopause along its track. Typhoon Utor played a key
role in pumping up air masses when it made landfall.
Finally, we investigated the observed profiles with and without the influence
of tropical cyclones. The relative frequency distribution of air parcels
sampled over Lhasa originating from the lower troposphere shows that the
maximum impact by typhoons is found at an altitude layer of 14.5–17 km
(365–375 K). Our findings confirm that air masses that originated from the
western Pacific region can also contribute to the composition of the ASM
anticyclone, as shown in several previous model studies
. Our results
also demonstrate that before landfall typhoons have a significant influence
on ozone near the tropopause layer. Under these conditions, typhoons cause
low ozone values (50–80 ppbv) near the layer of 370–380 K. However,
typhoons during landfall have a strong impact on air masses in the middle
troposphere. In our study, the transport pathways of air masses uplifted by
tropical cyclones into the ASM anticyclone were identified. Moreover, their
impact on the ozone values sampled over Lhasa in the ASM anticyclone during
August 2013 was quantified.
In the Tibetan Plateau region, there is a lack of dense in situ meteorological
observations, which might increase the uncertainties of meteorological
reanalysis data, especially for the vertical velocity . These
uncertainties in vertical velocities impact the results of the CLaMS
trajectory calculation. In addition, due to the lack of a detailed convective
scheme in CLaMS, especially the vertical transport in small-scale convective
clouds is underestimated. However, there is a lower limit for longer
timescale transport over several days or weeks. For example, transport from
the marine boundary layer to near the tropopause layer in Lhasa takes more
than 1 week according to the results of the CLaMS trajectory calculation.
In order to obtain the start point of the backward trajectories at the
locations of the measurement, ERA-Interim velocity fields must be
interpolated to the parcel locations. From this interpolation, an error of
the trajectory calculation will arise. To estimate this error, we also run a
bundle of trajectories of (i-Δi,j), (i,j-Δj), (i+Δi,j), and (i,j+Δj) around the locations of the measurement (i,j)
(Δi=Δj=1∘). We find that the bundle of trajectories
are nearly consistent with the backward trajectories starting at the
locations of the measurement (not shown here). Thus, the error caused by
interpolation should have a mirror impact on our conclusions. Every year,
about one-third of tropical cyclones form in the tropical and subtropical
western Pacific . Due to the limited number of ozone
profiles from Lhasa, it is still unclear how important the upward transport
by tropical cyclones is. Therefore, it is necessary to quantify the impact of
the western Pacific marine boundary layer air with uplifting and long-range
transport in controlling the chemical composition of the upper troposphere
within the ASM anticyclone. Case studies are certainly a first step toward
understanding the interplay between the ASM anticyclone and tropical
cyclones, but further research is required to explore the quantification and
intensities using long-term data records of ozone and water vapour. Only a
small number of in situ measurements in the region of the ASM anticyclone are
so far available. Therefore, future balloon and aircraft measurement
campaigns should focus on this region.
ERA-Interim meteorological reanalysis data are free available from the web page: http://apps.ecmwf.int/datasets/data/interim-full-daily/levtype=sfc/.
The AIRS Level-2 data used in this study can be obtained at
https://airsl2.gesdisc.eosdis.nasa.gov/data/Aqua_AIRS_Level2/. The SWOP data of this
paper are available upon request to Jianchun Bian (bjc@mail.iap.ac.cn). The CLaMS model data may be requested from Dan Li (lidan@mail.iap.ac.cn).
The authors declare that they have no conflict of
interest.
Acknowledgements
Ozone and water vapour data are from the SWOP campaign, which is funded by
the National Natural Science Foundation of China (91337214, 41675040,
41605025, 41275046, and 91637104). Our activities contribute to the
European Community's Seventh Framework Programme (FP7/2007-2013) as part of
the StratoClim project (grant agreement no. 603557). This work was supported
by the Chinese Scholarship Council and the German Academic Exchange Service
providing the 2014 Sino-German (CSC-DAAD) Postdoc Scholarship Program.
Finally, we wish to thank the two anonymous reviewers for very constructive
suggestions. The article processing charges for
this open-access publication were covered by a Research
Centre of the Helmholtz Association.Edited by: M. Chipperfield Reviewed by: two
anonymous referees
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