The new North American Land Data Assimilation System (NLDAS)
data in Giovanni provide another perspective on the sauna-like mixture of heat and humidity in July 2011 that bedeviled the central Plains states. The NLDAS hourly data provide high temporal resolution suitable for meteorological and hydrological research. The NLDAS models support water resources applications, numerical weather prediction studies, and water and energy cycle investigations.
The models also serve as a foundation for interpreting satellite and ground-based observations. An animation of daily NLDAS surface temperatures, constructed from NLDAS hourly data for the atmospheric layer just 2 meters above the land surface (Figure 1), shows that the epicenter of the heat wave in July was in Texas and Oklahoma, as the residents of those states surely knew. The color scale is in Kelvin (310 K is 98.3° F).
Figure 1. Animation of daily 2-meter surface air temperatures, July 2011, constructed from NLDAS hourly data.
A time-series of average daily temperatures for the Oklahoma region (Figure 2), also created from the NLDAS hourly data, shows there was very little relief during the entire month. The highest daily average temperature in these data was an astonishing 309 K (96.5° F). The average temperature for the month (red line shown in Figure 2) was 307.4 K (93.6° F). The National Climatic Data Center reported the average statewide July 2011 temperature for Oklahoma from weather station data was 88.9° F. (The analysis region for Figure 2 excludes the Oklahoma Panhandle; it was slightly cooler there, which is why the NCDC average temperature is lower than the average temperature derived from Figure 2).
Figure 2. Daily average surface temperatures over most of Oklahoma, July 2011, in Kelvin. The red line indicates the average temperature of the data points displayed in the plot.
The hourly animation of July 16-29 surface temperatures from NLDAS (Figure 3) shows the daily cycle of heating and cooling, and the increasing nighttime surface temperatures. The time shown is "Zulu" time or Greenwich Mean Time (GMT). Central Daylight Time is 5 hours after GMT, so, e.g., 05Z corresponds to 12:00 midnight CDT.
Figure 3. Animation of hourly NLDAS 2-meter surface air temperatures, July 2011.
An alternative way to look at the NLDAS hourly data is with a time-series. Figure 4 shows hourly surface temperatures for the central United States for July 2011. Of note in this figure are the lows that were higher than 300 K (80° F) – sultry nights in the Plains states. Both weather station and remotely sensed humidity data indicated that it was remarkably high humidity that sustained high nighttime temperatures.
Figure 4. Time-series of hourly NLDAS surface temperatures for the central United States, July 2011.
Images courtesy NASA Goddard Earth Sciences Data and Information Services Center (GES DISC) and Hydrological Sciences Branch, Goddard Space Flight Center.
The GES DISC is a NASA earth science data center, part of the NASA Earth Science Data and Information System (ESDIS) Project.