4.9 Analysis of diurnal conditions in Oklahoma City

Tuesday, 21 June 2005: 4:45 PM
South Ballroom (Hilton DeSoto)
Peter K. Hall Jr., Oklahoma Climatological Society, Norman, OK; and J. B. Basara

Prior to the Joint Urban 2003 field experiment, fifteen Portable Weather Information and Display Systems (PWIDS) were installed in and around the central business district (CBD) of Oklahoma City. PWIDS sites collected 10 second data over the course of eleven months. The PWIDS observations, as well as measurements taken by the Oklahoma Mesonet, were analyzed to isolate typical diurnal patterns for urban and rural environments.

Diurnal cycles of temperature, wind speed, and wind direction were examined for urban and rural sites. It was discovered that a strong diurnal signal existed in all variables measured in rural areas. For example, wind speed values changed by 2 meters per second during the day, while wind direction values varied by 30 degrees. Conversely, PWIDS sites in the CBD of Oklahoma City only measured a significant diurnal cycle for temperature; the magnitude of the wind oscillations within the CBD did not match the variation measured by the surrounding Mesonet sites. Finally, a diurnal cycle of temperature and wind differences was observed between the urban and rural areas. The magnitude of temperature differences was greatest at night, while the magnitude of wind speed differences was greatest during the day.

It is hypothesized that the diurnal cycle of wind direction depended more on the entry winds into the city than mixing occurring over the city. On the other hand, the diurnal cycle of temperature was quite similar between the urban and rural locations due to surface energy balances.

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