Analysis of the Relationship between the Cloud Water Path and Precipitation Intensity of Mature Typhoons in the Northwest Pacific Ocean

Abstract:

The relationship between precipitation intensity and cloud water in typhoon systems remains unclear. This study combined time- and space-synchronized precipitation and spectral data obtained by the Precipitation Radar (PR) as well as the Visible and Infrared Scanner (VIRS) onboard the TRMM satellite, to overcome the limitations of precipitation properties and cloud parameters not being synchronized in previous studies.

We presented the bispectral reflectance (BSR) algorithm to retrieve cloud microphysical properties using TRMM VIRS data. In this scheme, the visible and near-infrared radiative lookup table for COT and CER of water cloud and ice cloud are established with the Santa Barbara DISORT Atmospheric Radiative Transfer Model (SBDART), considering various geometrical conditions, surface types, and atmospheric states. After COT and CER are obtained from the reflectance at 0.63 μm and 1.6 μm in VIRS, the value of CWP is calculated by them.

The TRMM standard product of PR 2A25, provided by GSFC/NASA, was also used in this study. The similar cross-track scanning mode of VIRS and PR resulted in little lag in observing the same target, which made merging VIRS with PR feasible, using the resolution of the latter by weight-averaged method.

A merged dataset of near-surface rain rate (RR) and corresponding cloud water path (CWP) was established and used to analyze the potential correlation between cloud microphysical properties and precipitation, to deepen our understanding of the evolution of cloud to rain. In addition, 25 collocated satellite overpasses of mature typhoon cases in the Northwest Pacific Ocean from 1998 to 2012 were obtained, and the relationships between the CWP and RR of 144 515 pixels were analyzed in detail.

The results are shown as follows. Firstly, the retrieved CWPs of TRMM VIRS are almost identical to MOD06_L2 products, with a correlation coefficient of 0.88. Sencondly, CWP exhibits an oblique S-type change with the increasing RR and ultimately tends toward saturation. Thirdly, the CWP and RR of mature typhoon systems with different precipitation types, precipitation cloud phases, and vertical depths of precipitation can be fitted by a notable sigmoid function, which may be useful for estimating CWP and parameterizing precipitation in models.