Observing convective activities in complex convective organizations and their contributions to precipitation and anvil cloud amounts

Abstract

The convective processes of precipitation and the production of anvil clouds determine the Earth's water and radiative budgets. However, convection could have very complicated convective organizations and behaviors in the tropics. Many convective activities in various life stages are clustered and connected in complex convective organizations, and distinguishing their behaviors is difficult. In this work, based on hourly infrared brightness temperature (BT) satellite images, with a novel variable-BT tracking algorithm, complex convective organizations are partitioned into organization segments of single cold-core structures as tracking targets. The detailed evolution of the organization structures (e.g., the variation in the cold-core BT, mergers and splits of cold cores) can be tracked, and precipitation and anvil clouds are explicitly associated with unique cold cores. Compared with previous tracking algorithms that focused only on variations in areas, the novel variable-BT tracking algorithm is designed to track the core structure in complex convective organizations and document the evolution of both the area and BT structures. For validation, the tracked motions are compared against the radiosonde cloud-top winds, with a mean speed difference of −1.6 m s−1 and a mean angle difference of 0.5°. With the novel variable-BT tracking algorithm, the behaviors of oceanic convection over the tropical western Pacific Ocean are investigated. The results show that the duration, precipitation and anvil amount of lifetime accumulation all have simple loglinear relationships with the cold-core-peak BT. The organization segments of the peak BT values less than 220 K are long-lived, with average durations of 4–16 h, whereas the organization segments of the warmer-peak BT values disappear rapidly within a few hours but with a high occurrence frequency. The decay process after the cold-core peak contributes to more precipitation and anvil clouds than the development process does. With the core peaking at a colder BT, the differences in the accumulated duration, precipitation and anvil production between the development and decay stages increase exponentially. Additionally, the occurrence frequency of mergers and splits also has a loglinear relationship with the cold-core-peak BT. For the life cycles of the same cold-core-peak BT, the lifetime-accumulated precipitation and anvil amount are strongly enhanced in complicated life cycles with the occurrence of mergers and splits, compared with those with no mergers or splits. For the total tropical convective cloud water budget, long-lived complicated life cycles make the largest contribution to precipitation, whereas long-lived complicated and short-lived simple life cycles make comparable contributions to the anvil cloud amount and are both important.