A Lagrangian analysis of cold cloud clusters and their life cycles with satellite observations

Abstract

Cloud movement and evolution signify the complex water and energy transport in the atmosphere‐ocean‐land system. Detecting, clustering, and tracking clouds as semicoherent clusters enable study of their evolution which can complement climate model simulations and enhance satellite retrieval algorithms, where there are gaps between overpasses. Using a cluster tracking algorithm, in this study we examine the trajectories, size, and brightness temperature of millions of cloud clusters over their lifespan, from infrared satellite observations at 30 min, 4 km resolution, for a period of 11 years. We found that the majority of cold clouds were both small and short lived and that their frequency and location are influenced by El Niño. Also, this large sample of individually tracked clouds shows their horizontal size and temperature evolution. Long‐lived clusters tended to achieve their temperature and size maturity milestones at different times, while these stages often occurred simultaneously in short‐lived clusters. On average, clusters with this lag also exhibited a greater rainfall contribution than those where minimum temperature and maximum size stages occurred simultaneously. Furthermore, by examining the diurnal cycle of cluster development over Africa and the Indian subcontinent, we observed differences in the local timing of the maximum occurrence at different life cycle stages. Over land there was a strong diurnal peak in the afternoon, while over the ocean there was a semidiurnal peak composed of longer‐lived clusters in the early morning hours and shorter‐lived clusters in the afternoon. Building on regional specific work, this study provides a global long‐term survey of object‐based cloud characteristics.

Event‐Based Evaluation of the GPM Multisatellite Merged Precipitation Product From 2014 to 2018 Over China: Methods and Results

“…In addition, given the limitations of the study period, some results are calculated by gathering all the events from all the valid gridboxes across China, while a future study with a sufficient number of samples should further investigate the region‐specific event‐related features. Besides, since actual events not only develop during a period of time but also exist and advect over a range of spatial extents, further research should consider both the temporal and spatial event features, probably using a quasi‐Lagrangian framework to more accurately represent the meteorological events (Esmaili et al., 2016; Lochbihler et al., 2017).…”

The Role of Mesoscale Convective Systems in Precipitation in the Tibetan Plateau Region

“…This has, for example, been discussed in Esmaili et al. (2016), who presented a global cloud cluster tracking with unrealistically high amounts of convective cloud clusters over the TP during winter when only brightness temperatures are used. The atmospheric transmittance at wavelengths corresponding to the IR channels used for tracking (∼10.8 μm) is relatively high, while surface emissivity at these wavelengths is generally low for dry regions (Schädlich et al., 2001).…”

“…However, using universal thresholds can be problematic in a mountain environment like the TP, where low surface temperatures from high mountain tops can be confused with high cloud tops from deep convective clusters, particularly at night and during winter. This has, for example, been discussed in Esmaili et al (2016), who presented a global cloud cluster tracking with unrealistically high amounts of convective cloud clusters over the TP during winter when only brightness temperatures are used. The atmospheric transmittance at wavelengths corresponding to the IR channels used for tracking (∼10.8 μm) is relatively high, while surface emissivity at these wavelengths is generally low for dry regions (Schädlich et al, 2001).…”

Large‐Scale Characteristics of Tropical Convective Systems Through the Prism of Cloud Regime

“…Moreover, as shown in Table 2, the rate of incorrect filling decreases as the size of convective system grows. The likely reason for greater regime persistence from Terra to Aqua as the system grows in size is the longer lifetime of bigger systems (e.g., Chen & Houze, 1997; Esmaili et al, 2016). We also examined the geographical distribution of transition consistency of TCR1, TCR2, and TCR3 as a group from Terra to Aqua and found that the consistent transitions occurred more frequently in the warm pool oceans (not shown).…”