The Long-term Climatology of Mid-Mississippi Valley Dew points and the Implications for Regional Climate .

Dew point temperature is a measure of how much moisture is in the atmosphere at a given time and place. It is defined as the temperature the air would have to be cooled to, without the further addition of water vapor, before condensation could take place (e.g. Ahrens, 2009). The atmosphere can hold a certain amount of moisture at any given temperature before it becomes saturated, and this relationship is described as an exponential function of temperature and derivable from the First Law of Thermodynamics. In this context, saturation means that evaporation equals condensation at the liquid water – atmosphere interface. From a practical standpoint, it means that the atmosphere can hold approximately twice (one-half) the amount of water vapor for every 10 C rise (drop) in surface temperature. The atmosphere is considered saturated when the dew point temperature equals the ambient temperature. The climatological behavior of dew point temperature is an important quantity to examine because water vapor is the most important greenhouse gas. Water vapor may not necessarily correlate strongly to temperature on the time scale of weather since is not evenly distributed throughout the atmosphere. The amount of water vapor in the atmosphere will vary with time and location, however, most of this gas is found within the lowest 1 – 2 km of the atmosphere (e.g. Hurrell et al., 1995). On the time-scale of climate, the dew point may correlate more strongly with air temperature, but not perfectly. An climatological examination of this quantity across Missouri has not been performed recently, and a survey of the literature reveals that there are not many climatological studies of this quantity. Most studies of this quantity relate to short term weather prediction or variations (e.g. Stensrud and Yussouf, 2003). The climatological behavior of atmospheric water vapor amounts and the implications for the impact on climate change have been discussed recently in publications such as IPCC (2007) or GCCIUS (2009). Additionally, it has been theorized that the atmospheric water cycle would be more vigourous in a warmer world (GCCIUS, 2009). Thus, __________________________________________________ *Corresponding author address: Anthony R. Lupo, Department of Soil, Environmental, and Atmospheric Science, 302 E ABNR Building, University of Missouri, Columbia, MO 65211. E-mail: LupoA@missouri.edu. the implication would be that in a warmer world, the dew point temperature would be higher along with the observed air temperatures. Then, the goal of this work is to examine the climatological behavior for dew point temperatures in the Mid-Mississippi valley region. Several studies have been performed in order to examine the long-term behavior of snowfalls (e.g. Berger et al., 2002; Lupo et al. 2005), tornadoes (e.g. Akyuz et al. 2004), or temperatures and precipitation (e.g. Lupo et al. 2007, 2008; Birk et al. 2010) in this region. Following the methodologies of these studies, we will demonstrate that there is strong El Niño-related and possibly interdecadal variability in dew point temperatures. Additionally, we will demonstrate that there has been a statistically significant increase in dew point temperatures.