Optical and Geometrical Properties of Cirrus Clouds over the Tibetan Plateau Measured by Lidar and Radiosonde Sounding at the Summertime in 2014

Abstract

Abstract. Optical and geometrical characteristics of cirrus clouds over Naqu (31.48°N,92.06°E), the Tibetan Plateau were determined from lidar and radiosonde measurements performed during the third TIbetan Plateau EXperiment of atmospheric sciences (TIPEX III) campaign from July to August 2014. For the analysis of the temperature dependence, the simultaneous observations by lidar and radiosonde were conducted. Cirrus clouds were generally observed ranging from 9.7 to 16.5 km above sea level (a.s.l.), with the cirrus middle temperatures in the range from −79.7 to −26.0 C  . The cloud thickness generally 15 differed from 0.12 to 2.55 km with a mean thickness of 1.22  0.70 km and 85.7% of the case studies had thickness smaller than 1.5 km. The retrievals of linear particle depolarization ratio, extinction coefficient and optical depth of cirrus clouds were performed. Moreover, the multiple scattering effect inside of cirrus cloud was corrected. The linear particle depolarization ratio of the cirrus clouds varied from 0.36 to 0.52, with a mean value of 0.44  0.037. The optical depth of all the cirrus clouds was between 0.01 and 3 following the scheme of Fernald-Klett method. Sub-visual, thin and opaque cirrus clouds were 20 observed at 9.52%, 57.14% and 33.34% of the measured cases, respectively. The temperature and thickness dependencies on optical properties were studied in detail. A maximum cirrus thickness of around 2 km was found at temperatures between −60 and −50 C  . This study shows that the cirrus mean extinction coefficient of the cirrus clouds increase with the increase of temperature. However, our measurements indicate that the linear particle depolarization ratio has the opposite change tendency along with temperature. The relationships between the presence of cirrus clouds and the temperature anomaly and deep 25Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2017-355 Manuscript under review for journal Atmos. Meas. Tech. Discussion started: 11 December 2017 c Author(s) 2017. CC BY 4.0 License. 2 convective activity are also discussed. The formation of cirrus clouds is also investigated and it has apparent relationship with the dynamic processes of Rossby wave and deep convective activity over the Tibetan Plateau. The cloud radiative forcing is calculated by Fu-Liou model and increases monotonously with the increase of optical depth.

Temporal and vertical distributions of the occurrence of cirrus clouds over a coastal station in the Indian monsoon region

“…When the signal encounters a cloud, the NRB signal level begins to increase significantly due to the larger droplets in clouds compared with ambient air. As a result, using MPL observations, the cloud-base height of the lowest cloud is directly identified as the change in the slope or gradient (the first derivative) of the NRB (i.e., dNRB/dz), referred to as the differential zero-crossing method (Dai et al, 2019;Nair et al, 2012;Platt et al, 1994;Wu et al, 2015). To identify the base of cirrus clouds over the tropics, we limit the lowest altitude to 8 km; over this region, cirrus clouds usually occur at a temperature below −20 • C, corresponding to an altitude above 8 km (Liou, 1986;Lynch, 2002;Pandit et al, 2014).…”