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Communication Dans Un Congrès Année : 2019

In-situ Measurements of the HDO/H2O Isotopic Ratio in the Asian Summer Monsoon Trace Strong Convective Activity

Sergey Khaykin

Résumé

The Asian Monsoon Anticyclone is one of the main pathways by which water vapor enters the lower stratosphere, but the processes that lead to the formation of a moisture anomaly in the lower stratosphere are not understood in detail. The StratoClim high-altitude aircraft campaign in summer 2017 provided the first in-situ tracer measurements in the upper troposphere/lower stratosphere (UT/LS) region over the Asian monsoon region. Eight flights in July—August sampled a wide range of monsoon behavior, with diversity in airmass origin (Northwest India to China) and time since last convective influence (from nearly a week to minutes-old outflows at tropopause altitudes). We report here on measurements from a number of instruments, but with a focus on the isotopic composition of water vapor measured by the Chicago Water Isotope Spectrometer (ChiWIS). The isotopic composition of water vapor is a sensitive tracer of convective activity that impacts water vapor concentrations. Isotopic measurements made during StratoClim demonstrate the strength and diversity of convective influences on the UT/LS. Isotopic composition in the overworld stratosphere is nearly constant at about -460 per mil throughout the campaign. However, values in the UT/LS show wild diversity over individual flights, ranging from -700 per mil in recent convective outflow to -350 per mil in more aged air that is several days from last convective influence, presumably reflecting the influence of sublimating convective ice. Vertical isotope profiles demonstrate substantial convective influence up to 400 K, but a sharp reduction in activity at higher potential temperatures; this conclusion is supported by numerous other tracers. On finer scales, isotopic measurements show intense mixing of water vapor from convective outflows into the background environment and recycling of water between the solid and vapor phase. While mean isotopic profiles are consistent with expectations from limb-sounding satellites, in-situ measurements in StratoClim show the range of fine-scale processes and conditions that make up that average and demonstrate that convection plays a strong role in shaping the characteristics of the monsoon UT/LS.
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Dates et versions

insu-04458249 , version 1 (14-02-2024)

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B. Clouser, C. E. Singer, Sergey Khaykin, M. Kraemer, A. Lykov, et al.. In-situ Measurements of the HDO/H2O Isotopic Ratio in the Asian Summer Monsoon Trace Strong Convective Activity. American Geophysical Union, Fall Meeting 2019, Dec 2019, San Francisco, United States. pp.abstract #A51K-2777. ⟨insu-04458249⟩
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