HR: 0800h
AN: GC51A-0162    [Abstracts]
TI: Can Stable Isotopes of Hydrogen and Oxygen Tell you Which way the Wind is Blowing or has Blown in the Past?
AU: * Lawrence, J R
EM: geos52@consolidated.net
AF: Department of Geosciences, University of Houston, Houston, TX 77204-5007, United States
AU: Bowman, K P
EM: k-bowman@tamu.edu
AF: Department of Atmospheric Science, Texas A&M University, College Station, TX 77843- 3150, United States
AU: Gedzelman, S D
EM: sdgbrg@aol.com
AF: Department of Earth and Atmospheric Sciences, City College of New York, New York, NY 10031, United States
AB: The region off the Pacific southwest coast of Mexico has greater tropical cyclone activity per unit area than any other region of the world. This is in part due to high sea surface temperatures (Elsberry et al., 1987). From May to November frequent periods of intense convection occur over the ocean near Puerto Escondido. The disturbances take the form of storms associated with the ITCZ, mesoscale convective complexes and tropical depressions, storms, and hurricanes (Zehnder et al., 1999). Water vapor samples were collected at Puerto Escondido around 0300, 1200 and 1900 UTC every day from 10 to 31 July 1998. They were analyzed for their hydrogen and oxygen isotope ratios. Over that time period there were large variations in isotope values. Trajectory analysis demonstrated that the large variations were directly related to the intensity of precipitation over the previous 48 hours upwind of the collection site. In addition a distinct contrast in the average isotope values existed before and after July 18. The isotope values were on average markedly lower during the first period. This shift was directly related to the shift in circulation regimes. In the first period air in Puerto Escondido originated to the south and west over the Pacific Ocean. In the second period air generally came from the east across the Mexican Isthmus or Guatemala from the Caribbean Sea (Lawrence et al, 2004). The above trajectory analysis has been extended to include June to September months for the years 1995 to 2006. Trajectories were calculated at 6-hourly hourly intervals. During these four-month periods the wind direction at Puerto Escondido for the most part shifted from the southwest quadrant to the northeast quadrant, lasting from a few days to about two months. It is hypothesized therefore that the isotope value of water vapor in Puerto Escondido undergoes a distinct shift in response to the shift in wind direction as described above. Also it is hypothesized that the magnitude of this shift will be related to the extent of exposure of the air parcel to rain. The stable isotopic composition of leaf water in trees in the tropics in theory is primarily controlled by the isotopic composition of water vapor in the atmosphere, and this isotopic signal in the leaf water is transferred to the tree cellulose as the tree grows. Therefore, the potential exists to document past circulation regimes along the southwest coast of Mexico by the isotopic analysis of tree cellulose. The long-range objective of such isotopic analysis of trees would be to correlate the mesoscale circulation changes recorded in trees of the southwest coast of Mexico to synoptic scale circulation regimes thereby allowing for a better understanding of climate variability and trends.
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 3344 Paleoclimatology (0473, 4900)
DE: 3374 Tropical meteorology
DE: 4920 Dendrochronology
SC: Global Environmental Change [GC]
MN: 2007 Fall Meeting