Temperature dependence of tropical cirrus properties and radiative effects

Abstract

[1] The temperature dependencies of cirrus properties are studied using a dual polarization lidar and Mesosphere Stratosphere Troposphere (MST) radar at the tropical station Gadanki (13.5°N, 79.2°E). Cirrus clouds are generally observed in the altitude region 10 to 18 km, with midcloud temperature in the range À85°to À40°C. The cloud temperature decreases with increase in cloud altitude as expected. The mean cloud thickness is generally in the range 0.7 to 1.7 km. For temperatures in the range À75°to À50°C the cloud thickness is $1.7 km and shows a tendency to decrease at lower temperatures. The linear depolarization ratio (LDR) within the cloud shows a small increase with decrease in temperature. The cloud extinction and optical depth increases with increase in temperature. The temperature dependence of cirrus extinction/optical depth has been parameterized using different analytical forms such as exponential, linear, and polynomial, which shows that a second-order polynomial function is well suited for describing the temperature dependence of extinction coefficient/optical depth of tropical cirrus. The climate sensitivity factor derived based on the empirical relations shows an increase with decrease in cloud optical depth. The present study, however, indicates that the cirrus becomes radiatively significant when its optical depth exceeds a threshold value of 0.03.

Optical and geometrical characteristics of cirrus clouds over a Southern European lidar station

“…Our results are in agreement with Sassen and Comstock (2001) who have also presented the dependence of cloud thickness on mid-cloud temperature. Sunilkumar and Parameswaran (2005) studied tropical cirrus clouds and found that this peak is shifted to lower temperatures, in the range of −50 • to −70 • C. The conclusion of Sunilkumar and Parameswaran (2005) that mid-latitude cirrus clouds are generally warmer and thicker than those over the tropics is in agreement with our results. However, we should keep in mind that the number of samples corresponding to temperatures below −60 • C is limited.…”

“…9b there are indications that the cloud optical depth increases as the mid-cloud temperature increases. Other studies have also investigated the dependence of optical depth on mid-cloud temperature and found that these parameters are connected either linearly (Sassen and Comstock, 2001) or through a second-order polynomial function (Sunilkumar and Parameswaran, 2005;Platt et al, 1987). Finally, the dependence of the ratio of optical depth to thickness (mean extinction coefficient) as a function of mid-cloud temperature is examined.…”

“…Barrett and Ben-Dov, 1967;Viezee et al, 1969;Davis, 1969;Fernald et al , 1972;Platt, 1973;Platt, 1979;Klett, 1981;Fernald, 1984;Grund and Eloranta, 1990;Ansmann et al, 1992). Some key microphysical parameters are the extinction coefficient, lidar ratio and depolarization ratio as well as the mid-altitude and the corresponding mid-cloud temperature of cirrus clouds (Sunilkumar and Parameswaran, 2005). The lidar and depolarazation ratios are considered to be of special importance since are related to microphysics properties of the ice crystals contained on cirrus clouds, while mid-altitude and mid-temperature play an important role in determining cloud radiative properties.…”

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

“…With the 15 increase of the height, the temperatures gradually decrease. According to the previous work (Chen et al, 2002, Sunilkumar and Parameswaran, 2005, Seifert et al, 2007, He et al, 2013, temperature has great impact on linear particle depolarization ratio and extinction coefficient by dominating the crystal shape, number concentration and other microphysics properties of cirrus. Furthermore, the cloud base and top height of the first cirrus layer are 6.02  0.60 km and 8.56  0.69 km, respectively.…”

“…Polarization and Raman lidars have been employed to detect geometrical and optical properties of cirrus clouds by applying the methods that have been earlier demonstrated by Ansmann et al (1992). Several key 20 optical parameters such as the extinction coefficient, lidar ratio and depolarization ratio as well as the mid-altitude and the corresponding mid-cloud temperature of cirrus clouds were measured (Sunilkumar and Parameswaran, 2005). The depolarization ratios are considered to be of special importance since are related to microphysics properties of the ice crystals Atmos.…”