American Geophysical Union Become an AGU Member
Subscribe to AGU Journals		 AGU Home AGU Publications

Subscriber Access to Full Article (Nonsubscribers may purchase for $9.00, Includes print PDF, file size: 538552 bytes)

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 107, NO. D19, 4400, doi:10.1029/2001JD000565, 2002

Stable isotope composition of waters in the Great Basin, United States 1. Air-mass trajectories

Irving Friedman

U.S. Geological Survey, Denver, Colorado, USA


Joyce M. Harris

Climate Monitoring and Diagnostic Laboratory, NOAA, Boulder, Colorado, USA


George I. Smith

U.S. Geological Survey, Menlo Park, California, USA


Craig A. Johnson

U.S. Geological Survey, Denver, Colorado, USA


Abstract

Isentropic trajectories, calculated using the NOAA/Climate Monitoring and Diagnostics Laboratory's isentropic transport model, were used to determine air-parcel origins and the influence of air mass trajectories on the isotopic composition of precipitation events that occurred between October 1991 and September 1993 at Cedar City, Utah, and Winnemucca, Nevada. Examination of trajectories that trace the position of air parcels backward in time for 10 days indicated five distinct regions of water vapor origin: (1) Gulf of Alaska and North Pacific, (2) central Pacific, (3) tropical Pacific, (4) Gulf of Mexico, and (5) continental land mass. Deuterium (δD) and oxygen-18 (δ18O) analyses were made of precipitation representing 99% of all Cedar City events. Similar analyses were made on precipitation representing 66% of the precipitation falling at Winnemucca during the same period. The average isotopic composition of precipitation derived from each water vapor source was determined. More than half of the precipitation that fell at both sites during the study period originated in the tropical Pacific and traveled northeast to the Great Basin; only a small proportion traversed the Sierra Nevada. The isotopic composition of precipitation is determined by air-mass origin and its track to the collection station, mechanism of droplet formation, reequilibration within clouds, and evaporation during its passage from cloud to ground. The Rayleigh distillation model can explain the changes in isotopic composition of precipitation as an air mass is cooled pseudo-adiabatically during uplift. However, the complicated processes that take place in the rapidly convecting environment of cumulonimbus and other clouds that are common in the Great Basin, especially in summer, require modification of this model because raindrops that form in the lower portion of those clouds undergo isotopic change as they are elevated to upper levels of the clouds from where they eventually drop to the ground.

Published 12 October 2002.

Index Terms: 1854 Hydrology: Precipitation (3354); 1040 Geochemistry: Isotopic composition/chemistry; 1833 Hydrology: Hydroclimatology; 3354 Meteorology and Atmospheric Dynamics: Precipitation (1854).

Subscriber Access to Full Article (Nonsubscribers may purchase for $9.00, Includes print PDF, file size: 538552 bytes)

Citation: Friedman, I., J. M. Harris, G. I. Smith, and C. A. Johnson (2002), Stable isotope composition of waters in the Great Basin, United States 1. Air-mass trajectories, J. Geophys. Res., 107(D19), 4400, doi:10.1029/2001JD000565.