Distribution of tropical cirrus in relation to convection

Daily values of Halogen Occultation Experiment (HALOE) aerosol extinction and Climate Diagnostics Center (CDC) outgoing longwave radiation (OLR) data are used to quantify the statistical and geographical relationships of tenuous cirrus to OLR for pressure levels near the equatorial tropopause. Daily locations of deep convection are identified by analysis of the CDC OLR data. Analysis of the HALOE and CDC data demonstrates that cirrus extinction is larger over deep convection than over clearer regions by a factor of 3. Deep convection, however, occupies only 7% of the equatorial region. Ninety percent of the cirrus clouds near the tropopause are located outside of regions of deep convection. Estimates of the equivalent H2O amount in the cirrus are calculated by applying transformations from extinction to volume density. Averaged over the HALOE 2 km vertical field of view, the amount of equivalent H2O in cirrus is 0.1-0.2 ppmv, which is 2 to 5% of the local gas phase H2O. Five-day back trajectories near the tropopause are calculated for 1995-2000. Half of the HALOE cirrus observations over the maritime continent are consistent with formation by convective blow-off, while the other half are consistent with in situ formation processes.