An assessment of factors limiting tropical congestus cloud-top heights

I investigate the capping mechanisms behind mid-level cumulus congestus clouds. Two theories are analyzed using two months (January-February 2007) of collocated data between the Atmospheric InfraRed Sounder (AIRS) onboard Aqua and the Cloud Profiling Radar (CPR) onboard CloudSat, as well as data from the European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis (a, ERA) Interim Reanalysis.;The first theory is that dry, free-tropospheric air caps convection due to increased detrainment of unsaturated air at cloud-top, limiting the cloud's buoyancy. This theory is given credence by the sharp differences in AIRS relative humidity (RH) between three cloud categories separated by CPR cloud-top height. Broad layers are noted where the difference in local RH is statistically significant. Congestus occurs more frequently than deep convective clouds when the free-tropospheric RH is less than 30%. Mean RH from the ERA reanalysis shows that RH increases in the midtroposphere (around 600 hPa) by a specific difference of 3% in RH in the presence of deep clouds, compared to RH in the presence of congestus.;The second theory is that a decreased vertical temperature lapse rate, dT/dp, would slow cloud growth, creating a mode of cloud-top heights at the stable layer as clouds lose buoyancy. The signal for lapse rate changes in the AIRS data, however, is not as strong as the signal for RH differences. Near 600-400 hPa, roughly the region where congestus cloud-top heights are located, no significant difference in lapse rates is noted between congestus and deep clouds; in fact, the mean values suggest that congestus clouds appear in more unstable atmospheres than deep clouds. Only slight differences in temperature and lapse rate are noted in ERA data as well. These results suggest that drier air may play a greater role in limiting congestus cloud-top heights than increased atmospheric stability.;Five years of relative humidity (RH) observations from the Atmospheric Infrared Sounder (AIRS) instrument aboard the Aqua satellite are then analyzed to identify areas of anomalously dry air between 600 and 400 hPa over deep convective regions of the tropical oceans. Back trajectories are then calculated for each observed parcel.