JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 102, NO. C12, PAGES 26,861-26,875, NOVEMBER 30, 1997 Air mass trajectories to Summit, Greenland: A 44-year climatology and some episodic events Jonathan D. W. Kahl 1, Dewayne A. Martinez •, Hampden Kuhns 2, Clifford I. Davidson 2, Jean-Luc Jaffrezo 3, and Joyce M. Harris 4 Abstract. The seasonal variation in atmospheric transport patterns to Summit, Greenland, is examined using a 44-year record of daily, 10-day, isobaric back trajectories at the 500- hPalevel. Over 24,000 modeled trajectories are aggregated intodistinct patterns using cluster analysis. Ten-day trajectories reaching Summit arelongest during winter, with 67% extending upwind (westward) as far backasAsia or Europe. Trajectories are shortest during summer, with 46% having 10-day origins over North America. Duringall seasons a small percentage (3-7%) of trajectories originate in west Asia/Europe and follow a meridional pathover the Arctic Ocean before approaching Summit fromthenorthwest. Trajectories at the 700-hPa level tend to be shorter thanat 500 hPa,with manyof the 700- hPatrajectories fromNorthAmerica tracking over theNorthAtlantic andapproaching Summit fromthe south.The long-range transport climatology for Summit is similar to a year-round climatology prepared for Dye 3, located 900 km to the south [Davidson et al., 1993b]. An analysis of several aerosol species measured at Summit during summer 1994 reveals examples of theusefulness and also the limitations of using long-range air trajectories to interpret chemical data. 1. Introduction Polarice cores provide an invaluable record of past atmospheric conditions. TheU.S. Greenland Ice Sheet Project 2 (GISP2) and the European Greenland Ice Core Project (GRIP) have retrieved cores of over 3 km in depth from the Summitregion of Greenland. Analyses of chemical species, radioisotopes, trace elements, particulate matter, and other parameters within these cores have derailed climatic conditions extending as far back as 250 kyr with possible seasonal time resolution duringthe last glaciation. The papers in this special section are all devoted to topics pertaining to these cores. Oneimportant process which can potentially distort atmospheric properties preserved in theglacial record is air-to-snow transfer [Dibb and Jaffrezo, this issue]. While some information is available concerning deposition of gaseous [Neffel et al., 1995] and aerosol [Davidson et al., 1993a; Bergin et al., 1995]species, increased understanding of air-snow transfer functions is needed to properly interpret atmospheric properties preserved in ice cores. IDepartment of Geosciences, University of Wisconsin- Milwaukee 2Department ofCivil Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania •Laboratorie de Glaciologie etG6ophysique de l!Environnement, Domaine Universitaire, St. Martin d•eres, France nClimate Monitoring and Diagnostics Laboratory, National Oceanic and Atmospheric Administration, Boulder, Colorado Copyright 1997by theAmerican Geophysical Union. Paper number 97JC00296. 0148-0227/97/97JC-00296509.00 Long-range atmospheric transport is a fundamental component of the air-snow transfer process. The air and snow preserved in the GISP2 and GRIP ice cores contain components and impurities that originated in distant source regions and were carded by the atmospheric circulationto the air column over the Summit region. Variations in the physical and chemical composition of the ice cores must to a large extent reflect variationsin atmospheric circulation patterns. To date, a comprehensive studyof long- range atmospheric transport to the Summit region has not been performed. The primary goal of this paper is to present an analysis of over 40 years of atmospheric trajectories in order to identify source regions contributing chemical constituents to Summit, Greenland. These isobaric, upwindair trajectories describe the 10-daytransport pathways of air masses arriving daily at Summit during the period 1946-1989. The seasonal variation in trajectory pathways is described, andour results are compared to a similaranalysis of seasonal transport routes for the southern portion of the Greenland Ice Sheet [Davidson et al., 1993b]. This analysis includes an evaluation of the sensitivity of transport to trajectory altitude andthe resulting change in source regions that it infers. A secondary goalof thispaper is to analyze the relationship between 10-day isentropic trajectories andchemical signals of specific tracers recorded in the atmosphere at Summit during a portion of theATM program [DibbandJaffrezo, this issue]. Specific episodes are presented and the validityand limitation of this approach are discussed in termsof source regions. Futurework using this long-term trajectory data set will focus on the interannual variability in transport routes and on the relationship between trajectory patterns and chemical constituents in surface snow and in snow pits. 26,861