Thomas N. Chase
Ph.D. Colorado State University, 1999
Associate Professor, Department of Civil, Environmental and Architectural Engineering
E-mail: tchase@cires.colorado.edu
Office: Ekeley S262
Phone: 303-492-1274
Web: Chase Research Group
Research Interests
Much of my recent work has addressed the climatic effects of landcover change both through climate model studies and observational analysis. I am particularly interested in atmospheric circulation changes which may have resulted from recent landcover changes and interactions with other natural circulation regimes such as those due to El Nino/Southern Oscillation or monsoons. Because changes in tropical circulation have been strongly related to the recently observed planetary surface warming, this research is relevant to the issues of greenhouse warming. A main issue for the future is adequately characterizing the changes in land surface properties over the course of time.
I have also been involved in examining general feedback behavior to changes in the climate system, particularly as mediated by the hydrological cycle. Because the hydrological cycle is strongly coupled to the biosphere, landcover change has many implications for hydrological cycle feedbacks and may explain some discrepancies between model simulations and observed behavior. One example of a regulation mechanism mediated by the hydrological cycle under investigation here is seen in observations of mid-tropospheric Arctic winter temperatures where a minimum is reached in late autumn which is not exceeded later in the winter despite several months of continued net energy loss. This minimum temperature can be related to convective activity over open ocean and suggesest the presence of an active regulation mechanism.
Current Research: Land and Ocean Surface Impacts on Global Hydrology
Figure 1: Irrigation percentage in India.
Figure 2: Monthly anomalies in the occurrence of two or more consecutive days in Denver, CO during which low-level daytime inversions were present. Y-axis is fraction of days per month, and x-axis is calendar year. Locally weighted regressions smooth the original data using a 0.7 span.
We continue to examine the impact of surface hydrology on climate, particularly in the massively irrigated regions of Asia, and have found evidence of substantial impacts, both in observational and model simulation studies. For example, irrigation in India (Figure 1) seems to have reduced monsoon rainfall and slowed the East Asian Jet maximum, indicating that circulations around the globe can be affected by human disturbances to the land surface in remote areas.
We have continued examining minimum temperature regulation by convection at high latitudes and have updated our observational analysis of this phenomenon in the last year. This work documents that mid-tropospheric temperatures at high latitudes reach a minimum (about -40°C) early in the winter and then never get much colder, despite the lack of solar input for months. We hypothesize that this is due to convective heating driven by sea-surface temperature slightly below 0°C in cold air masses that migrate over the ocean. Surface air rises adiabatically to reach the observed minimum by 500 mb. We are proposing to extend this hypothesized mechanism to maximum temperatures and lower latitudes in future work.
Finally, we also have been looking into low-level inversions in the Western United States, which we found to have substantially decreased in frequency—but increased in strength—over the period of record in six Western cities (Figures 2 and 3 show trends in inversion frequency and strength in Denver, CO). This is of interest because air quality in the West is a function of inversion frequency and strength, and because climate models have predicted that inversions would be more frequent in a warming climate.
Publications
Click here for a complete list of published works »
Chase is also one of the CIRES Faculty who teach at the University of Colorado at Boulder with teaching loads equivalent to those of CU faculty rostered solely in departments and programs.
