The impact of wind speed on nighttime microscale temperature gradients

This study focuses on nighttime temperatures observed across a 0.02 km^2 parcel of sloped oak woodland known as the Crosstimber Micronet. The Micronet is located in central Oklahoma and is surrounded by five Oklahoma Mesonet stations that are situated on relatively flat, grassy terrain. Surface observations at five stations within the Micronet and at the five surrounding Mesonet sites were collected from 2002-2005. These observations were used to analyze the impact of wind speed on the nighttime temperature gradient across the Micronet.

The analysis revealed that the nighttime temperature gradient across the Micronet was a function of the mesoscale wind speed, defined as the average wind speed across the five surrounding Mesonet sites. When this value was greater than 5 m/s or less than 2.5 m/s, the temperature gradient across the Micronet was relatively weak (i.e., less than 3°C). But when the mesoscale wind speed was between 2.5-5 m/s, the gradient was strong (i.e., 3-11°C across a horizontal distance of less than 200 m).

This range of wind speeds corresponded to nights when winds were calm across the southern end of the Micronet but non-calm across the northern end. Thus, it should not be assumed that the largest microscale temperature gradients occur on calm nights.