Composition of the TTL over Darwin: local mixing or long-range transport? 1SEAES, University of Manchester, Manchester, UK
2ICG-2, Forschungszentrum Jülich, Jülich, Germany
3Institute of Atmospheric Physics, DLR Oberpfaffenhofen, Oberpfaffenhofen, Germany
Received: 26 Feb 2009 – Published in Atmos. Chem. Phys. Discuss.: 20 Mar 2009 Abstract. We present ozone and carbon monoxide measurements taken in Darwin,
Australia, during the wet season of 2005/2006, to examine whether the
composition of the Tropical Tropopause Layer (TTL) reflects that of the
local boundary layer or is influenced more by advection from distant
sources. We find that the latter predominates in the upper TTL, and is also
the major influence in the lower TTL, except during an active monsoon phase.
The day-to-day variability of ozone in the TTL is far greater than that in
the lower troposphere, and correlates closely with air mass origin deduced
from trajectory calculations based on standard ECMWF wind analyses. Although
clear evidence of recent local uplift was found in carbon monoxide tracer
measurements recorded inside convective anvils, no such signal was found
out-of-cloud in the background TTL, where the measured variability
correlated well with air mass origin deduced from back-trajectories. This
study suggests that the composition of the TTL is ultimately determined by
vertical mixing in certain "hot spot" regions of the tropics, with advection
from these regions dominating the composition elsewhere.
Revised: 26 Aug 2009 – Accepted: 25 Sep 2009 – Published: 19 Oct 2009
Citation: Heyes, W. J., Vaughan, G., Allen, G., Volz-Thomas, A., Pätz, H.-W., and Busen, R.: Composition of the TTL over Darwin: local mixing or long-range transport?, Atmos. Chem. Phys., 9, 7725-7736, doi:10.5194/acp-9-7725-2009, 2009.