On the characterization of descending nature of cirrus clouds over a tropical site, Gadanki

ABSTRACT

An interesting feature of the tropical cirrus clouds is its descending nature, which is not well characterized over the tropics due to the scarcity of continuous observations over a single location. In order to quantify the morphological characteristics of the descending cirrus, data from systematic ground-based Lidar observations of cirrus clouds over a tropical site Gadanki (13.5° N, 79.2° E) is analyzed during 2000–2015. Time series and altitude structures of different descending cirrus layers are discussed. A total of 105 cases of descending cirrus (about 9%) are observed against 10 (about 1%) cases of ascending cirrus. The mean displacements of the base and top of descending cirrus clouds are 1.26 ± 1.04 km and 1.21 ± 0.99 km, respectively. About 94% of the descending cirrus have their descent speeds of < 0.8 m s⁻¹. As 75% of descending cirrus has Cloud Optical Depth (COD) between 0.1 and 0.9, it is obvious that most of the observed descending cirrus clouds are classified as either thick or thin clouds. Surprisingly, none of the cases showed that descending cirrus are of a sub-visible type. The present exploratory study on descending nature of cirrus clouds would be useful in understanding the process of cirrus sedimentation, which plays a major role in regulating the moisture content in Tropical Tropopause Layer (TTL) as well as on the Earth’s radiation budget.

Acknowledgements

One of the authors, NMK, acknowledges NARL authorities for providing the data through https://www.narl.gov.in. Authors express their gratitude to NASA Langley Research Center for providing the CALIPSO data through https://www-calipso.larc.nasa.gov and the two anonymous reviewers for scientifically shaping the work as is presented now.

Disclosure statement

No potential conflict of interest was reported by the authors.