Showing papers by "Steven T. Massie published in 2002"

Distribution of tropical cirrus in relation to convection

Abstract: [1] 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.

Transport of water vapor in the tropical tropopause layer

Abstract: [1] A trajectory model coupled to a simple micro-physical model is used to explore the observed relationship between convection, water vapor and cirrus clouds in the tropical tropopause layer (TTL). Horizontal transport associated with the local Hadley circulation leads to water vapor minima in the winter hemisphere separated from the convective regions and the region of minimum temperatures. These spatial signatures are consistent with observations of water vapor and cirrus in the TTL from the Halogen Occultation Experiment (HALOE). In the simulations, one third of observed ice is formed due to horizontal transport through cold regions. Applied variations in temperature over time scales longer than a few hours, similar to gravity wave induced perturbations, act to lower the simulated water vapor.

Satellite observation of dehydration in the Arctic Polar stratosphere

Abstract: [1] We report the first space-borne observation of dehydration in the Arctic polar stratosphere. In January 1997, the Improved Limb Atmospheric Spectrometer (ILAS) observed up to ∼3 ppmv water vapor reduction during ice cloud formation and ∼2 ppmv permanent removal of water vapor, mostly at altitudes between 23 and 26 km. In some cases, the dehydrated air was downwind from mountain wave induced Polar Stratospheric Cloud (PSC) events. Furthermore, simultaneous observations of HNO3 and H2O show that the gas phase reduction of HNO3 in the Arctic (January 1997) was much smaller than that observed in the Antarctic (June 1997) when a similar level of water vapor reduction occurred.