Analysis of new observational datasets relating to the organization and dynamical impacts of tropical convection
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Deep convection is a major heat source in the tropical atmosphere, driving circulation cells that are an important aspect of Earth's climate. The environmental conditions that modulate the occurrence of lightning, which is associated with vigorous convection, are examined using observations from WWLLN, a ground-based lightning network. Diurnal lightning climatologies illustrate the interplay between sea breezes, mountain-valley wind regimes, and remotely forced gravity waves in touching off thunderstorms in a wide variety of geographical settings. Over the Maritime Continent, 850-hPa wind speed and area-averaged cloudiness are shown to be inversely related to day-to-day lightning frequency over land. Both lightning and rainfall, which is observed by the TRMM satellite, are suppressed windward of, and enhanced leeward of mountain ranges. These relationships are also observed during the active and break periods of the intraseasonal Madden-Julian Oscillation (MJO). The relationship between lightning and nitrogen oxide radicals, which are associated with ozone production, over the Maritime Continent is examined based on WWLLN observations and tropospheric NO2 data from the GOME-2 satellite. Composites of the daily NO2 regressed onto lightning frequency reveal a plume of enhanced NO2 following a day of enhanced lightning. Lightning and NO2 also vary coherently with the MJO, with variations of up to ~50% of the annual mean. MJO-related deep convection induces planetary-scale Kelvin and Rossby waves in the stably stratified tropical tropopause transition layer (TTL). The structure of these waves is investigated using satellite observations from COSMIC, CALIPSO, and MLS, as well as ERA-Interim wind and humidity fields. Regions of ascent in the planetary waves are associated with anomalously low temperatures, high radiative heating rates, enhanced cirrus occurrence, and high carbon monoxide and low ozone concentrations. Low water vapor concentrations lag the low temperature anomalies by ~1-2 weeks. Anomalies in each field tilt eastward with height in the TTL and propagate downward from the lower stratosphere to the upper troposphere. As the Kelvin wave front propagates eastward across equatorial South America and Africa, equatorially-symmetric, anomalously low temperature and water vapor mixing ratio and enhanced TTL cirrus are observed above ~100 hPa in the zonal-mean.
- Atmospheric sciences