18th Conference on Weather and Forecasting, 14th Conference on Numerical Weather Prediction, and Ninth Conference on Mesoscale Processes

Wednesday, 1 August 2001
Observational analyses of the fine-scale wind and moisture characteristics in MAP IOP-2B and IOP-8
Joseph J. Charney, North Carolina State University, Raleigh, NC; and Y. -. L. Lin, C. M. Hill, and J. A. Thurman
The precipitation characteristics evident in the synoptic-scale observations of MAP IOP-2B and MAP IOP-8 suggest that while the two events exhibit similar overall characteristics, there are considerable differences in both the dynamic and thermodynamic details within the events. Both of the IOPs involve considerable amounts of orographically-enhanced precipitation in northern Italy, which can be attributed to a southerly moist inflow ahead of an advancing synoptic-scale frontal system. However, moisture present in each of the cases is considerably different, such that the overall static stability characteristics were almost completely opposite; generally stable conditions prevailed in IOP-8 while considerable instability was present in IOP-2B. This study will address the extent to which the special observations taken as part of the MAP field study can demonstrate the differences in the moisture and flow characteristics in the two cases, with the goal of addressing the meso-b and meso-g scale influences on the precipitation development throughout the region.

By assimilating wind observations collected from instrumented aircraft, lidar, and derived from doppler radar with wind profiler, soundings, and other more traditional surface observations, we will address the small-scale characteristics of the flow patterns in the two IOPs. Specifically, the extent to which very fine scale variations in the slope of the terrain was correlated with the magnitude of the observed precipitation is addressed. In addition to the wind observations, detailed analyses of the moisture distribution from the radiosondes and, if necessary, numerical simulations of the events will be employed to assess stability characteristics and the role they played in the fine-scale evolution of the precipitation. Additionally, the mesoscale analyses will provide an opportunity to verify our numerical simulations of orographic heavy rainfall.

Finally, the observations will be used to assess the local spatial and temporal variations in the southerly moist inflow observed in both of the events, to assess the role of these fine-scale variations on the overall character of the events. Synoptic-scale observations and preliminary mesoscale simulations of the events indicate that potential vorticity streamers are present in the mid and upper troposphere. The aircraft observations will enable us to more completely assess the role of these features in the development of the precipitation. Also, by carefully investigating the characteristics of the moist inflow into the region, we will be able to address whether the smaller mountain ranges in southwestern and central Italy played a role in the precipitation evolution of the event. Sensitivity studies using additional numerical simulations can be used to more vigorously assess the role of these comparatively small orographic features and to identify the moist flow regimes based on the propagation of orographically-induced convective systems, as proposed in a parallel study.

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