Ice nucleation and dehydration in the Tropical Tropopause Layer

• DOI: 10.1073/pnas.1217104110
• Publication Date: 2013-01-23T07:27:25Z
• Authors: Eric J. Jensen; Glenn Diskin; R. Paul Lawson; Sara Lance; T. Paul Bui; Dennis Hlavka; Matthew McGill; Leonhard Pfister; Owen B. Toon; Rushan Gao
• Keywords: Cirrus; Tropopause; Ice nucleus; Ice cloud; Saturation (graph theory)

Optically thin cirrus near the tropical tropopause regulate humidity of air entering stratosphere, which in turn has a strong influence on Earth’s radiation budget and climate. Recent high-altitude, unmanned aircraft measurements provide evidence for two distinct classes formed region: ( i ) vertically extensive with low ice number concentrations, extinctions, large supersaturations (up to ∼70%) respect ice; ii layers much higher concentrations that effectively deplete vapor excess saturation. The persistent supersaturation former class is consistent long time-scales (several hours or longer) quenching saturation given cold temperatures. low-concentration clouds are likely background population insoluble particles less than 100 L −1 (often 20 ), whereas high concentration (with up 10,000 can only be produced by homogeneous freezing an abundant aqueous aerosols. These measurements, along past high-altitude indicate occur frequently region, high-concentration infrequently. predominance means may typically allow entry into stratosphere as ∼1.7 times mixing ratio.