Dynamic and thermodynamic features of low and middle clouds derived from atmospheric radiation measurement program mobile facility radiosonde data at Shouxian, China

Abstract

By using the radiosonde measurements collected at Shouxian, China, we examined the dynamics and thermodynamics of single- and two-layer clouds formed at low and middle levels. The analyses indicated that the horizontal wind speed above the cloud layers was higher than those within and below cloud layers. The maximum balloon ascent speed (5.3 m s⁻¹) was located in the vicinity of the layer with the maximum cloud occurrence frequency (24.4%), indicating an upward motion (0.1–0.16 m s⁻¹). The average thickness, magnitude and gradient of the temperature inversion layer above single-layer clouds were 117±94 m, 1.3±1.3°C and 1.4±1.5°C (100 m)⁻¹, respectively. The average temperature inversion magnitude was the same (1.3°C) for single-low and single-middle clouds; however, a larger gradient [1.7±1.8°C (100 m)⁻¹] and smaller thickness (94±67 m) were detected above single-low clouds relative to those above single-middle clouds [0.9±0.7°C (100 m)⁻¹ and 157±120 m]. For the two-layer cloud, the temperature inversion parameters were 106±59 m, 1.0±0.9°C and 1.0±1.0°C (100 m)⁻¹ above the upper-layer cloud and 82±60 m, 0.6±0.9°C and 0.7±0.6°C (100 m)⁻¹ above the low-layer cloud. Absolute differences between the cloud-base height (cloud-top height) and the lifting condensation level (equilibrium level) were less than 0.5 km for 66.4% (36.8%) of the cases analyzed in summer.