Todd Mitchell

Research Scientist

Observations to study nature

Todd MitchellTodd Mitchell is a research meteorologist at JISAO who analyzes observations of temperatures, precipitation, and other physical variables to describe and try to explain phenomena in the ocean-atmosphere system. The problems of interest range in spatial scale from surface air temperatures over land that influence stream temperatures to global scale phenomena such as the El Niño / Southern Oscillation (ENSO) and the long-term rise in CO2. The data employed can be daily-averages or averages over longer periods, such as months, seasons, and years.

An example of the kind of problem Dr. Mitchell studies is the documentation and physical attribution of the ongoing drought in the southeast United States. Figure 1 below shows monthly precipitation averaged over Mississippi, Alabama, Georgia, and Florida for 2003 through 2007. The gray bars are the monthly average precipitation in centimeters (cm) and the black line is the average precipitation in each calendar month based on the average of 30 years of data. It typically rains about 11 cm each month in this region and it is a little wetter in the summer. The summer of 2003 was wetter than normal, and it can be seen that, beginning in September 2005, the region has experienced normal or below normal precipitation in almost all of the months.

As of early February 2008, there are wildfires in northern Florida and along the South Carolina coast, and the state of North Carolina has enacted an outdoor burning ban to prevent the accidental ignition of wildfires. Dr. Mitchell is working with a group of university and National Oceanic and Atmospheric Administration scientists to characterize the spatial and temporal scales of the drought, and to see if the deficit of precipitation can be attributed to predictable large-scale patterns in ocean surface temperatures.

monthly precipitation graph for Mississippi, Alabama, Georgia, and FloridaThe ocean temperatures are very cold at the high latitudes (less than 10 Celsius (50 degrees Fahrenheit)) and very warm in the tropics (warmest temperatures in excess of 30 Celsius (86 degrees Fahrenheit)), and this is true in all years. The differences in ocean temperatures from one year to the next are much smaller than this range, and can be identified by plotting the difference in temperature in each region from the long-term average.

The temperature departures are as large as 1 Celsius in magnitude. The colder than normal temperatures in the central and eastern equatorial Pacific are associated with the cold El Niño / Southern Oscillation (ENSO) cycle that is underway. By comparing the temperatures with those in other dry years and wet years in the southeast, it appears that a common feature of the temperatures in the dry years is above normal ocean temperatures to the northeast of the Philippines and the north Atlantic, and below normal temperatures off of the Washington and Oregon coast. The temperature deviations near the Philippines can modify the local distribution of rainfall which can influence patterns of rainfall throughout the Northern Hemisphere. Hoerling and Kumar (2003) identified changes of temperatures in this region as responsible for drought in the southeast and other portions of the extratropical Northern Hemisphere in 1998-2002.

global sea surface temperature for 2007The map of temperature deviations is complicated and other scientists in the group are using computer models of the atmospheric circulation to independently see which of these regions seems to be responsible for the 2007 drought. By understanding the causes of the drought, scientists can hopefully provide government and the public with information on whether the drought can be expected to continue or dissipate in 2008.

Dr. Mitchell's contribution to this problem was to select appropriate precipitation and temperature datasets to document the drought and ocean temperatures, to characterize the normal and drought precipitation, and to construct simple empirical analyses to identify ocean regions that exhibit a consistent behavior with respect to precipitation variations in the southeast. An understanding of large-scale atmospheric and oceanic processes is integral to interpreting the patterns that come out of these analyses.

Dr. Mitchell's education and work experience have exposed him to a broad variety of climate phenomena. Todd received his B.S. in Atmospheric Sciences at Oregon State University in 1980; worked on radiative modeling of CO2 and ocean carbon sequestration at the NASA Goddard Institute for Space Studies in 1980-81 (A. Lacis, J. Hansen, I. Fung); and ran a simple radiative-dynamical atmospheric climate model at Atmospheric and Environmental Research / Massachusetts Institute of Technology (W.-C. Wang, P. departures from the 2007 temperaturesStone) in 1982. Todd received his Ph.D. under Dr. J.M. (Mike) Wallace at the University of Washington in 1990, with an observational study of how the semi-permanent marine rainfall regions and strong equatorial ocean circulation interact, and produce the observed seasons in the equatorial Pacific and Atlantic Oceans and South America. Todd served a National Research Council post-doctoral position at the NASA Goddard Space Flight Center under W.K.M. Lau 1990-92. Todd joined JISAO in 1993 and worked with Mike Wallace on a large variety of observational problems, including ENSO variability, the interaction of hurricanes and the global ocean, and aerosols. Todd has served on the Climate Variability Committee of the American Meteorological Society, interacted with scientists at the Peruvian Institute of Geophysics to study El Niño and the climate of Peru, and contributed to reports of the National Academy Sciences and to the Intergovernmental Panel on Climate Change. In 2007, Todd began working with Nate Mantua on general problems of atmospheric and ocean variability, and on the specific problem of how climate affects fish.

In his free time, Todd enjoys cooking, growing vegetables, spending time with his friends and family, backpacking in the great Northwest, and he is trying to figure out how best to contribute to the effort to improve the health of Puget Sound. He hopes that someday his right knee will quit bothering him so he can climb some more glaciated mountains.