Effect of deep convection on the tropical tropopause layer composition over the southwest Indian Ocean during austral summer

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.

Sensitivity of Summertime Convection to Aerosol Loading and Properties in the United Arab Emirates

“…The IBRT values dropped to around 190 K, indicating rather cold cloud tops, a sign of very deep convection [78], with the thick high-level clouds shaded in brown in the RGB images. Such low values of IRBT are more typical of tropical convective activity, such as that seen in tropical disturbances [79], than the average summertime convection in the UAE [31]. A second but less intense round of convection occurred in the evening to nighttime hours, with isolated convective cells developing over eastern UAE and western Oman in early to mid-afternoon hours, when convection typically flares up here [31].…”

Unprecedented Observations of a Nascent In Situ Cirrus in the Tropical Tropopause Layer

“…Further details on the model set‐up are described in Evan et al. (2020). Here, 100,000 air parcels were distributed randomly within boxes with a depth of 500 m and 0.10° × 0.10° longitude‐latitude bins centered on the balloon at the cold‐point tropopause when the cirrus was observed.…”

“…To compute the FLEXPART trajectories, the ECMWF meteorological fields are retrieved at 0.50° and 0.15° and on full model levels (137 vertical model levels with a top at 0.01 hPa). Further details on the model set-up are described in Evan et al (2020).…”