HR: 1340h
AN: B23A-0935    [Abstracts]
TI: The Impact of Coastal Meteorology on CO$_{2}$ Net Ecosystem Exchange Estimates: Implications for global inversion studies
AU: * Riley, W J
EM: wjriley@lbl.gov
AF: Lawrence Berkeley National Lab, Earth Sciences Division 90-1106 1 Cyclotron Rd, Berkeley, CA 94720 United States
AU: Randerson, J T
EM: jranders@uci.edu
AF: University of California, Irvine, Earth System Science Dept. 3212 Croul Hall, Irvine, CA 92697-3100 United States
AB: A number of recent atmospheric inversion studies have concluded that there is a large northern hemisphere terrestrial sink for atmospheric CO$_{2}$. Many of the flask observations used in these analyses are collected at coastal stations or at remote offshore islands. Even though these sites are critical for our interpretation of continental-scale patterns of CO$_{2}$ fluxes, most of the work to quantify diurnal and synoptic variability in atmospheric CO$_{2}$ has been done at mid-continent locations and therefore the impacts of air-sea breezes, local topography, and transport of CO$_{2}$ from adjacent terrestrial ecosystems near the coastal domain are not well understood. Flasks are typically opened in the middle of the day, under windy conditions when sea-breeze circulations are common, and in locations with substantial topographic discontinuities, such as coastal bluffs and coastal mountain ranges. However, global transport models cannot resolve air-sea breezes, coastal discontinuities, and recirculation from nearby ecosystems. To determine the extent to which these factors impact the global inversions we apply a well-tested modeling framework that includes coupled meteorological (MM5), land-surface (ISOLSM), and tracer models. The MM5-ISOLSM model provides consistent predictions of net ecosystem CO$_{2}$, latent energy, and sensible energy exchanges at very fine resolutions. We apply the modeling framework to investigate atmospheric CO$_{2}$ sampling at Trinidad Head, CA over four months spanning the seasons in 2002. Our results demonstrate that sea and land breezes significantly impact atmospheric CO$_{2}$ concentrations, including those sampled in the middle of the day with an onshore breeze. Further, transport of CO$_{2}$ originating from ecosystem respiration north of Trinidad Head substantially impacts measured atmospheric CO$_{2}$. Variations from background associated with these `non-background' sources resulted in perturbations above background of 1.2, 0.5, 5.6, and 0.6 ppm during March, June, September, and December 2001, respectively, under strong onshore wind conditions. We characterize conditions (e.g., seasons, synoptic meteorology, topographical) where variations from expected background concentrations can be expected. This work will (1) help assess the impact of flask sampling criteria (such as minimum wind speed) on measured CO$_{2}$ concentrations at coastal sites; (2) identify biases induced by these criteria on long-term averages; (3) quantify the role of coastal mountain ranges and smaller-scale topographic heterogeneities on surface CO$_{2}$ concentrations; and (4) identify conditions where CO$_{2}$ originating from nearby terrestrial ecosystems can impact coastal sampling.
DE: 1610 Atmosphere (0315, 0325)
DE: 1615 Biogeochemical processes (4805)
DE: 0315 Biosphere/atmosphere interactions
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting