Characteristics of Marine Low Clouds Under Various Environmental Conditions

• Main Authors: Jia-Ying Wu, 吳佳瑩
• Other Authors: Hung-Chi Kuo
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/8x9rm9

碩士 === 國立臺灣大學 === 大氣科學研究所 === 105 === This study aims to discuss the cloud structure transition of marine low clouds propagating equatorward from the subtropics. Using the three dimensional Vector Vorticity equation cloud-resolving Model (VVM), idealized experiments are performed to determine the timing of stratus cloud to cumulus-under-stratus transition. In the control experiment, sea surface temperature (SST) increases as the large-scale subsidence decreases following the observational track calculated with the Lagrangian method. Sensitivity experiments are performed by modifying the total water mixing ratio difference (〖-∆q〗_t) and liquid water potential temperature difference (∆θ_l) between the free atmosphere and the boundary layer to evaluate the timing of stratus cloud breakup and cumulus-under-stratocumulus cloud development. The timing of the transition is determined by the liquid water path (LWP) probability density function (PDF) analyses. The results suggest that the stratus clouds breakup occurs around 44 minutes in the control run, and transits to cumulus-under-stratocumulus around 3 hours 28 minutes. While 〖-∆q〗_t increases (decreases) by 2.00 g kg-1, the timing of the stratus clouds breakup advances (postpones) 35 minutes (1 hour 20 minutes), and the timing of the cumulus-under-stratocumulus development advances (postpones) 1 hour 50 minutes (6 hours 25 minutes). In the experiments when the ∆θ_l decreases 4.98 K, the timing of stratus cloud breakup and cumulus-under-stratocumulus development both advances. While 〖-∆q〗_t stays the same (decreases by 2.00 g kg-1), the timing of the stratus clouds breaking advances 50 minutes (1 hour 40 minutes), and the timing of the cumulus-under-stratocumulus development advances 1 hour 30 minutes (7 hours 20 minutes). The timing of the cumulus-under-stratocumulus development is 3.8 times faster as well as the boundary layer height raises 1.7 times faster than the experiments which have higher ∆θ_l. The above experiments suggest that the transition of the marine boundary clouds are influenced by both 〖-∆q〗_t and ∆θ_l. On the other hand, the development of boundary layer depth is mainly influenced by ∆θ_l.