Abstract
Abstract. Balloon-borne measurements of cryogenic frost-point hygrometer (CFH) water vapor, ozone and temperature and water vapor lidar measurements from the Maïdo Observatory on Réunion Island in the southwest Indian Ocean (SWIO) were used to study tropical cyclones' influence on tropical tropopause layer (TTL) composition. The balloon launches were specifically planned using a Lagrangian model and Meteosat-7 infrared images to sample the convective outflow from tropical storm (TS) Corentin on 25 January 2016 and tropical cyclone (TC) Enawo on 3 March 2017. Comparing the CFH profile to Aura's Microwave Limb Sounder's (MLS) monthly climatologies, water vapor anomalies were identified. Positive anomalies of water vapor and temperature, and negative anomalies of ozone between 12 and 15 km in altitude (247 to 121 hPa), originated from convectively active regions of TS Corentin and TC Enawo 1 d before the planned balloon launches according to the Lagrangian trajectories. Near the tropopause region, air masses on 25 January 2016 were anomalously dry around 100 hPa and were traced back to TS Corentin's active convective region where cirrus clouds and deep convective clouds may have dried the layer. An anomalously wet layer around 68 hPa was traced back to the southeast Indian Ocean where a monthly water vapor anomaly of 0.5 ppmv was observed. In contrast, no water vapor anomaly was found near or above the tropopause region on 3 March 2017 over Maïdo as the tropopause region was not downwind of TC Enawo. This study compares and contrasts the impact of two tropical cyclones on the humidification of the TTL over the SWIO. It also demonstrates the need for accurate balloon-borne measurements of water vapor, ozone and aerosols in regions where TTL in situ observations are sparse.
Highlights
Deep convection plays an important role in delivering water and other chemical constituents to the tropical tropopause layer (TTL; ∼ 14–19 km altitude; Fueglistaler et al, 2009) and lower stratosphere regions
We present cryogenic frostpoint hygrometer (CFH) measurements from two soundings performed in austral summers 2016 and 2017, when deep convection was active near Réunion Island
Balloon-borne measurements of CFH water vapor, ozone, and iMet temperature and water vapor lidar measurements showed that both storms humidified the TTL, with RHice values exceeding 50 % for tropical storm (TS) Corentin and 90 % for tropical cyclone (TC) Enawo in the upper troposphere
Summary
Deep convection plays an important role in delivering water and other chemical constituents to the tropical tropopause layer (TTL; ∼ 14–19 km altitude; Fueglistaler et al, 2009) and lower stratosphere regions. Recent studies based on Lagrangian models (Schoeberl et al, 2014; Ueyama et al, 2015) that include convection and cirrus clouds microphysics show that convection impacts TTL cirrus clouds and water vapor near the tropical tropopause by 10 %–30 % (∼ 1 ppmv). Liu and Zipser (2015) showed using radar observations from the Global Precipitation Measurement (GPM) satellite that deep convection deeper than 15 km (Fig. 1 in Liu and Zipser, 2015) can occur over the south IO with dozens of systems reaching above 17 km These systems are likely tropical cyclones over the southwest Indian Ocean (SWIO) or thunderstorms that are often observed over Madagascar during austral summer (Roca et al, 2002; Bovalo et al, 2012).
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