A study of meso-α-scale disturbances on the Baiu Front and their environmental field

Abstract

Several meso-α-scale lows (MAL), which developed along the Baiu Front in the year of 2001 are studied by an observational analysis and a numerical experiment. The observational analysis utilizes the GANAL and RANAL data which have a horizontal resolution of 125 km and 20 km, respectively. The observed MALs are found to be categorized into two types: One is accompanied by an upper-level disturbance, and has a trough tilting westward with increasing height. The other is not accompanied by an upper-level disturbance, and has a trough tilting eastward with height. A MAL of the latter type that appeared on 20 June 2001 is examined in detail. This MAL had a horizontal pressure trough which runs in the southwest-northeast direction. It was associated with a cold temperature anomaly at the low-level to the east side of the low center, which is consistent with the eastward tilting trough in view of the hydrostatic balance. A numerical simulation using a 5 km-mesh Japan Meteorological Agency Non-Hydrostatic Model, without a cumulus parameterization, successfully reproduced the observed characteristics of the MAL. A budget analysis of the thermodynamic equation shows that the cold anomaly at the low-level in the east side of the MAL, is caused by an adiabatic cooling associated with the strong updraft induced by a condensational heating in the mid- and upper-levels. © 2007, Meteorological Society of Japan.