Abstract
Abstract. Thin cirrus clouds in the Tropical Tropopause Layer (TTL) have important ramifications for radiative transfer, stratospheric humidity, and vertical transport. A horizontally extensive and vertically thin cirrus cloud in the TTL was detected by the Cloud Aerosol LIDAR and Infrared Pathfinder Satellite Observations (CALIPSO) on 27–29 January 2009 in the Tropical Eastern Pacific region, distant from any regions of deep convection. These observations indicate that the cloud is close to 3000 km in length along the CALIPSO orbit track. Measurements over this three day period indicate that the cloud event extended over a region from approximately 15° S to 10° N and 90° W to 150° W and may be one of the most extensive cirrus events ever observed. Coincident temperature observations from the Constellation of Observing Satellites for Meteorology, Ionosphere, and Climate (COSMIC) suggest that the cloud formed in-situ as a result of a cold anomaly arising from a midlatitude intrusion. The event appears to last for up to 2 days and the temperature observations do not show any indication of the expected infrared heating. It is hypothesized that the cloud could be maintained by either nucleation of numerous small ice crystals that don't sediment or by multiple localized ice nucleation events driven by temperature variability at scales smaller than the overall cloud field, producing small ice-crystal sizes which have sufficiently long residence times (≈53 h) to maintain the cloud. It is possible that the residence times are augmented by vertical motion which could also act to offset the expected infrared heating. Further observations of similar events will be required in order to conclusively explain this curious cloud.
Highlights
Cirrus clouds have been predicted and observed in the Tropical Tropopause Layer (TTL) for almost 30 yr (Robinson, 1980; Winker and Trepte, 1998; Fueglistaler, 2009)
Horizontally extensive, and vertically thin cirrus cloud in the TTL was detected by CALIPSO on 27–29 January 2009 in the Tropical Eastern Pacific region
Variations in the large-scale circulation linked with tropical intrusions generated an anomalously cold region in the tropical tropopause layer over the Eastern Pacific on 26–31 January 2009
Summary
Cirrus clouds have been predicted and observed in the Tropical Tropopause Layer (TTL) for almost 30 yr (Robinson, 1980; Winker and Trepte, 1998; Fueglistaler, 2009). TTL cirrus are typically thin lamina, with low optical depths These thin, often subvisible clouds can have optical depths of less than 0.03 (Sassen and Cho, 1992) and are the most common form of cloud in the TTL (Wang and Dessler, 2006). Due to their transient nature and complex morphology, the climate impacts of TTL cirrus are poorly understood (Stubenrauch et al, 2007). Regardless of how TTL cirrus are formed, their vertical thickness is typically less than 1 km and their horizontal scale is commonly less than 100 km (Massie et al, 2010)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
