Oceanic Mesoscale Convective Systems Research Articles

A Comparison Of WSR-88D Reflectivities, SSM/I Brightness Temperatures, and Lightning for Mesoscale Convective Systems in Texas. Part I: Radar Reflectivity and Lightning

Abstract This is the first part of a two part study. Part I compares radar data from the League City, Texas, WSR-88D and cloud-to-ground (CG) lightning data for a set of eight mesoscale convective systems (MCSs), which occur at various stages of development along the upper Texas gulf coast. Vertical profiles of radar reflectivity (VPRR) as well as plan views and vertical cross sections are constructed to characterize the structure and relative strength of each MCS. The VPRR are also compared with similar profiles from tropical oceanic MCSs. The data show that in all the majority of negative CG lightning flashes are located near high-reflectivity convective cores (>35 dBZ) in the mixed-phase region (0°C ≤T≥ −20°C). Growing or mature MCSs typically had larger negative flash counts and higher percentages of negative lightning (≥80%) associated with convective core than MCSs at later stages of their life cycle. Comparison of the median VPRR for the various MCSs showed that although each case had high-reflecti...

Precipitation and Kinematic Structure of an Oceanic Mesoscale Convective System. Part I: Momentum Transport and Generation

Abstract This is the second paper of a two-part series documenting the structure of and momentum transport by a subtropical mesoscale convective system near Taiwan, using Doppler radar data and in situ data from the NOAA P-3. Part I defines the basic system structure and evolution. In Part II, the momentum transport by the system is estimated and related to system structure, and the momentum budget for a portion of the embedded convective band is evaluated. Profiles of the vertical flux of horizontal momentum are constructed from in situ data, Doppler radar data, and both combined, in a coordinate system with u normal to the line and positive eastward, since the low-level air is feeding the line from the east. Differences in the fluxes from the two sources appear to be mainly due to an underestimation of the mean vertical velocity from the Doppler radar data. The discrepancy results partially from the concentration of convergence in the boundary layer—precisely where the Doppler cannot adequately sample t...

Precipitation and Kinematic Structure of an Oceanic Mesoscale Convective System. Part I: Convective Line Structure

Abstract The precipitation, thermodynamic, and kinematic structure of an oceanic mesoscale convective system is studied using airborne Doppler and in situ (flight-level) data collected by the NOAA P-3 aircraft. The system, a well-organized, stationary, north-south convective line, was located near the east coast of Taiwan. In Part I, the basic structure of the line is documented with both datasets, a procedure revealing the strengths and weakness of both approaches. The Doppler data reveal that the warm, moist air feeding the line enters from the east side. Most updrafts associated with the leading edge of the convective line tilt westward below 5 km and then eastward above 5 km. This change of tilt corresponds to a change in the sign of the vertical flux of east-west momentum. To the east of the leading edge, a 10-km-wide zone of strong mesoscale descent is seen. The band is not a complete barrier to the low-level southeasterly flow, and at times and places along the line the inflowing air can move throu...

Microphysics in an oceanic mesoscale convective system during the Taiwan area mesoscale experiment

The microphysical processes in both the melting layer and the warm‐rain region of an oceanic mesoscale convective system observed during the Taiwan Area Mesoscale Experiment (TAMEX) are studied using airborne observations. Two flight cases are used, one flown in the transitional region and the other in the stratiform region. In the melting layer the particle number density decreases by an order of magnitude from the top to the bottom of the layer. This is caused by the sharp increase of particle fall speed as snowflakes melt into rain. The ice water content is higher in the transitional region, thus cooling the environment more efficiently during melting. In the warm‐rain region the microphysical process is dominated by coalescence process. Large raindrops are generated and the corresponding median diameter of all raindrops increases by a factor of 2 to 3 from the bottom of the melting layer to the ground level. The breakup process is more efficient in the transitional region.