Cold Pool Properties from Oklahoma Mesonet Data

The 5-minute Oklahoma Mesonet data are examined for information about convective systems and boundary layer interactions. For the summer months an objective method produces a “cold pool score” to define cold pool boundaries using fronts. The method somewhat resembles that used by Engerer, Stensrud, and Coniglio (2008). These cold pool scores are currently generated using surface temperature falls, surface pressure rises, and surface wind vector changes over 30-minute intervals. Frontal passage at a station occurs if the cold pool score reaches a minimum threshold value and if the cold pool score is a maximum during the four-hour period centered on that timestep. If frontal passage occurs at all three stations in a mesonet triangle the front can be tracked as it progresses through the triangle.

Preliminary results show that strong surface convergence is generally observed ahead of the front with strong surface divergence behind the front. Frontal analysis appears to be able to capture fronts that are both synoptic and mesoscale in origin and matches up well with radar imagery. There was a wide range in frequency of frontal passages throughout the mesonet with the northern and western areas observing 2-4 times the frontal passages as the southeast. The median temperature drop was 7 K while the median pressure rise was 1.5 mb. The maximum changes were 13 K and 7 mb. Only a weak correlation was found between pressure and temperature changes. This indicates that the vertical structure of the temperature perturbation in the cold pools varies from case to case. Ongoing work will entail classifying cold pools according to the properties and life-cycle stage of the convective system, determining cold pool extent and area, and applying our analysis methodology to a longer time period. The results could prove useful for evaluating the representation of cold pools in cumulus parameterizations and cloud-resolving models.