Detectability and Configuration of Tropical Cyclone Eyes over the Western North Pacific in TRMM PR and IR Observations

Abstract

Statistics for 138 cases from 61 tropical cyclones over the western North Pacific during the five years from 1998 to 2002 were used to determine the detectability and configuration of tropical cyclone (TC) eyes and to reveal relations with TC intensity and life stages in satellite-based infrared (IR) and precipitation radar (PR) observations from the Tropical Rainfall Measuring Mission (TRMM). Tropical cyclone eyes were detectable in PR data in 89% of cases and in IR data in 37% of cases. Maximum sustained wind speeds in TCs were much greater when the eye was detected in both IR and PR data than in cases when the eye was detected only in PR data or when no eye was detected in either PR or IR data. An eye was detectable in both IR and PR data in the developing stage of only 18% of TCs although an eye was present in the PR data in 90% of cases. An eye was detected in both IR and PR data in 51% of the TCs during the mature stage. During the decaying stage, an eye was detected in both IR and PR data in 31% of cases. Eye diameter determined from PR observations was larger during the later stages. Most TCs had an eye less than 82.5 km in diameter during the developing stage. Tropical cyclone eyes embedded within concentric eyewalls appeared more frequently in the mature and decaying stages; this is consistent with findings from previous studies. In most cases, eye diameter was smaller in IR observations than in PR observations because an upper cloud shield extending from the eyewall partially covered the eye. For several TCs with concentric eye walls, however, eye diameter was smaller in PR observations. A shallow inner eyewall in the PR data and a deep outer eyewall in both IR and PR data characterized these cases.