Abstract
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.
Highlights
The Tropical Tropopause Layer (TTL) is a transition region between the convectively-driven tropical troposphere and the radiatively-controlled stratosphere, where the chemicalCorrespondence to: W
On 22 November 2005 (Fig. 3b) boundary layer ozone concentrations around 40 ppbv were significantly lower than the TTL, which varied from 65–85 ppbv
The origin of uplifted back-trajectories reaching the TTL above Darwin show a consistent and coherent pattern that accounts for the variations in both recorded ozone concentrations and carbon monoxide concentrations
Summary
The Tropical Tropopause Layer (TTL) is a transition region between the convectively-driven tropical troposphere and the radiatively-controlled stratosphere, where the chemical. Acting to couple the tropospheric Hadley circulation with the wider stratospheric Brewer-Dobson circulation, the TTL acts as a major source region for air entering the stratosphere, influencing the concentration of trace constituents important for the chemical balance of the ozone layer as well as climate (Holton et al, 1995). The campaign was conducted from Darwin, Northern Australia (12.47◦ S, 130.85◦ E), in two periods: 10 November 2005–12 December 2005, and 20 January 2006–17 February 2006 It was based on measurements using ozonesondes and two research aircraft: a Dornier-228 carrying a suite of instruments capable of measuring chemical and aerosol constituents in the boundary layer and lower free troposphere (up to an altitude ∼4 km); and the Airborne Research Australia (ARA) Grob G520T Egrett, operated primarily in the region of main convective outflow (up to ∼15 km), and equipped with instrumentation for cirrus microphysical analysis, in addition to chemical and aerosol measurements. We use the term “background TTL” to describe measurements made outside convective outflow regions; as described later (see Sect. 4) clear evidence of local uplift was observed from Egrett measurements inside convective outflow but was seldom observed in clear air
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