Frequency of deep convective clouds in the tropical zone from 10 years of AIRS data

Abstract

Abstract. Deep convective clouds (DCCs) have been widely studied because of their association with heavy precipitation and severe weather events. Changes in the properties of DCCs are likely in a changing climate. Ten years of data collected by Atmospheric Infrared Sounder (AIRS) allow us to identify decadal trends in frequency of occurrence of DCCs over land and ocean. In the past, DCCs have been identified in the thermal infrared by three methods: (1) thresholds based on the absolute value of an atmospheric window channel brightness temperature; (2) thresholds based on the difference between the brightness temperature in an atmospheric window channel and the brightness temperature centered on a strong water vapor absorption line; and (3) a threshold using the difference between the window channel brightness temperature and the tropopause temperature based on climatology. Simultaneous observations of these infrared identified DCCs with the Advanced Microwave Sounding UnitHumidity Sounder for Brazil (AMSU-HSB) using 183 GHz water channels provide a statistical correlation with microwave deep convection and overshooting convection. In the past 10 years, the frequency of occurrence of DCCs has decreased for the tropical ocean, while it has increased for tropical land. The area of the tropical zone associated with DCCs is typically much less than 1 %. We find that the least frequent, more extreme DCCs show the largest trend in frequency of occurrence, increasing over land and decreasing over ocean.The trends for land and ocean closely balance, such that the DCC frequency changed at an insignificant rate for the entire tropical zone. This pattern of essentially zero trend for the tropical zone, but opposite land/ocean trends, is consistent with measurements of global precipitation. The changes in frequency of occurrence of the DCCs are correlated with the Niño34 index, which defines the sea surface temperature (SST) anomaly in the east-central Pacific. This is also consistent with patterns seen in global precipitation. This suggests that the observed changes in the frequency are part of a decadal variability characterized by shifts in the main tropical circulation patterns, which does not fully balance in the 10-year AIRS data record. The regional correlations and anticorrelations of the DCC frequency anomaly with the Multivariate ENSO Index (MEI) provide a new perspective for the regional analysis of past events, since the SST anomaly in the Nino34 region is available in the form of the extended MEI from 1871.

Trends in peroxyacetyl nitrate (PAN) in the upper troposphere and lower stratosphere over southern Asia during the summer monsoon season: regional impacts

“…This may be due to transport by stronger deep convective activity during the monsoon season as observed in radar, AVHRR, AIRS and MODIS (e.g., Devasthale and Fueglistaler, 2010;Hassim et al, 2014). The observed increasing frequency of overshooting convection over the tropical land mass (Aumann and Ruzmaikin, 2013) indicates an increasing trend in transport across the tropical tropopause in agreement with our results. Quantification of changes in UTLS-PAN due to overshooting convection is beyond the scope of this study.…”

“…The lightningproduced PAN is readily carried by convective updrafts to the lower stratosphere, where its lifetime is considerably longer (Labrador et al, 2005). The increase in frequency of deep convective clouds over the tropical land mass (Aumann and Ruzmaikin, 2013) may cause an increase in the frequency of vertical transport. Radar, AVHRR, AIRS and MODIS satellite observations show frequent overshoots deep into the tropical tropopause layer during monsoon season (Devasthale and Fueglistaler, 2010;Hassim et al, 2014).…”

Impact of tropical lower stratospheric cooling on deep convective activity: (I) Recent trends in tropical circulation

“…Aumann and Ruzmaikin (2013) reported that deep convection over land in the tropics shows an increasing trend, while that over tropical oceans shows an opposite decreasing trend based on 10 years of Atmospheric Infrared Sounder (AIRS) data.…”

Extreme Convection and Tropical Climate Variability: Scaling of Cold Brightness Temperatures to Sea Surface Temperature

“…This allows utilizing spaceborne measured radiances to study the variability of deep convective events (Aumann et al 2008;Aumann and Ruzmaikin 2013;Wong and Dessler 2005). This allows utilizing spaceborne measured radiances to study the variability of deep convective events (Aumann et al 2008;Aumann and Ruzmaikin 2013;Wong and Dessler 2005).…”