The differences in cloud vertical structures between active and break spells of the East Asian summer monsoon based on CloudSat data

Abstract

The description of the cloud vertical structure remains the key source of uncertainty in climate studies. Based on the CloudSat dataset, the differences in cloud vertical structures between the active and break spells of the East Asian summer monsoon are analyzed by using the composite analysis method. During the active spell, more clouds appear, the occurrence frequency of single-layer clouds significantly decreases, and the occurrence frequency of clouds with two and more layers obviously increases. The lowest layer of the cloud is thicker than the higher layer during the active spell, while the highest layer of the cloud is thicker than the lower layer during the break spell. The clouds in the southern region of the study area are thicker than the clouds in the northern region during the active spell and thinner than the clouds in the northern region during the break spell. From the active spell to the break spell, the clouds became sparser in the southern region but more compact in the northern region. During the active spell, the cloudiness anomaly demonstrates an obvious northward-tilting structure from the upper atmosphere to the lower atmosphere because the large value center of high clouds is located in the south of the study area, while the middle and low-level clouds are located in the center of the study area. Both convective precipitation and stratiform precipitation occur in the southern region during the active spell, while the northern region is mainly dominated by convective precipitation. The cloud ice water content increases during the active spell and decreases during the break spell. During the active spell, the cloud liquid water content (LWC) increases in most of the study area, and the positive LWC anomaly exhibits an apparent northward-tilting structure from the upper level to the lower level. During the break spell, the LWC decreases in the northern region, and the negative anomaly tilts northward from the upper level to the lower level. However, the shallow convective clouds in the southern region are not completely suppressed during the break spell, and abundant positive LWC anomalies are observed in the lower troposphere.