Publication Abstracts

Kelley 2003

Kelley, M., 2003: Water Tracers and the Hydrologic Cycle in a GCM. Ph.D. thesis. Columbia University.

The role of transport in determining atmospheric humidity has received considerable attention in light of the radiative importance of water vapor. Its ubiquitous source and short tropospheric lifetime render atmospheric water an informative transport tracer when "tagged" with the geographic origins of its surface evaporative input. Results from a GCM simulation of this source tracer and a vapor age tracer are presented, providing a complement to the flux and trajectory calculations commonly used to investigate humidity-circulation relationships. The tracer distributions are generally consistent with observations and theories of moisture transport if prevailing paradigms were to be slightly amended. Tropical vapor is lifted into the free troposphere in convective regions, and the age tracer in downwind clear-sky regions shows a gradual descent back into the boundary layer, but the subtropics themselves contain the chief convective sources for the subtropics. Extratropical vapor rises along slantwise paths indicative of baroclinic eddies, but also exhibits a continental convective contribution in the northern summer hemisphere. Stratospheric vapor originates almost exclusively in the tropics, but at a broad range of longitudes.

The vapor origin analysis is extended to a geographic survey of precipitation sources. Global patterns of the age and transport distance of precipitating water are also presented. Independently of climate and geography, the most likely moisture source for a given location is often rather local (∼1000 km distant) relative to geographically more variable mean transport distances of 2000-5000 km. Over land areas, this proximity of sources reflects a significant degree of "recycling," in agreement with previous studies. For precipitation variability, the locality is further suggested to qualitatively deemphasize the importance of nonlocal factors such as long-range transport.

Lastly, addressing a different topic, an aspect of the intensification of the hydrologic cycle with global temperature is investigated from energetic considerations. Control and doubled-CO2 GCM simulations are used to explore how the temperature dependence of evaporation over seasonal to interannual timescales differs from that over climate-change timescales. Using the surface energy budget, an upper bound upon changes in potential evaporation with climate is elucidated which partially explains the different temperature dependences at different timescales.

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BibTeX Citation

  author={Kelley, M.},
  title={Water Tracers and the Hydrologic Cycle in a GCM},
  school={Columbia University},
  address={New York, N.Y.},

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RIS Citation

ID  - ke04000r
AU  - Kelley, M.
PY  - 2003
BT  - Water Tracers and the Hydrologic Cycle in a GCM
PB  - Columbia University
CY  - New York, N.Y.
ER  -

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