Socioeconomic Impacts of Mesoscale Weather Systems and Regional Scale Climate Variations
CIMMS/OU Sponsored Research Incentive – Multiscale Evolution and Predictability of a Warm Season Climate Anomaly in the U.S. Southern Great Plains
Objectives
Investigate the multiscale events and interactions that culminated in the
Texas Hill Country flood during the summer of 2002; investigate why this
flood marked a discontinuous jump in the regional climate.
Accomplishments
The Texas Hill Country flood during summer 2002 was remarkable in its duration,
with 4-, 5-, 7-, and 10- day precipitation totals being more than twice
the published values of the 100-year event. It is also noteworthy for
ushering in a discontinuous jump in the regional climate from a prolonged
drought to a 6-week cool and wet climate anomaly.
This year the second objective – investigation of why this flood marked a discontinuous jump in the regional climate – has been our focus. Our initial investigation revealed a southwest orientation of positive relative vorticity in July across Texas from the Baja Peninsula. This indicated that the large-scale circulation for the North American Monsoon (NAM) might be contributing to the cool and wet regional anomaly. Previous research has linked the NAM to the Madden-Julian Oscillation (MJO) (Lorenz and Hartmann 2006). The 2002 MJO was very active and proxies for the MJO clearly indicate that Texas/Oklahoma were under the ascend phase (convectively active) during July of 2002. The figure below shows snapshots in July of the velocity potential field which is used as a proxy for the MJO. It is clear from this figure that the ascend phase of the MJO (indicated by negative values of the velocity potential field) was prevalent over the Texas/Oklahoma region during July. This upper air pattern, that was present through the end of July, would have provided a favorable environment for a cool and wet regional anomaly. Another paper (Zhou and Miller 2005) explored the interaction between the MJO and the Arctic Oscillation (AO). Consistent with this research, the active summer MJO for 2002 is coincident with a positive phase of the AO and a retraction of the East-Asian jet. This was in sharp contrast to the drought year of 1998 with an inactive MJO, a negative phase of the AO and an expansion of the East- Asian jet. This research suggests possible teleconnections might play a role in predisposing the Texas/Oklahoma region toward extremes in summer precipitation given other favorable synoptic conditions.
This project is ongoing.
PublicationsPortis, D., P. J. Lamb, L. Leslie, and P. Nutter, 2007: Multi-scale evolution and predictability of a warm season climate anomaly in the U.S. Southern Great Plains. J. Climate, to be submitted.
Velocity potential anomalies (0.2101 sigma) every five days for the date shown. Anomalies are departures from 1968-1996. Blue, dashed contours indicate convective regions (ascend phase of the MJO) and red, solid contours indicate regions of suppressed convection (descend phase of the MJO).