Showing papers by "David J. Erickson published in 1993"

A stability dependent theory for air‐sea gas exchange

Abstract: The influence of thermal stability at the air-sea interface on computed values of the transfer velocities of trace gases is examined. The novel “whitecap” model for air-sea gas exchange of Monahan and Spillane (1984), extended here to include thermal stability effects, is linked with an atmospheric general circulation model to compute global transfer velocity patterns of a climate reactive gas, CO2. The important terms in the model equations such as the whitecap coverage, friction velocity, neutral and local drag coefficients and the stability parameter ψm(Z/L) are discussed and analyzed. The atmospheric surface level air temperature, relative humidity, wind speed and sea surface temperature, obtained from the National Center for Atmospheric Research Community Climate Model 1 (CCM1) are used to drive algorithms describing the air-sea transfer velocity of trace gases. The transfer velocity for CO2 (kCO2) is then computed for each 2.8° × 2.8° latitudinal-longitudinal area every 24 hours for 5 years of the seasonal-hydro runs of the CCM1. The new model results are compared to previously proposed formulations using the identical CCM1 forcing terms. Air-sea thermal stability effects on the transfer velocity for CO2 are most important at mid-high wind speeds. Where cold air from continental interiors is transported over relatively warm oceanic waters, the transfer velocities are enhanced over neutral stability values. The depression of computed kCO2 values when warm air resides over cold water is especially important, due to asymmetry in the stability dependence of the drag coefficient. The stability influence is 20% to 50% of kCO2 for modest air-sea temperature differences and up to 100% for extreme cases of stability or instability. The stability dependent “whitecap” model, using the transfer velocity coefficients for whitecap and nonwhitecap areas suggested by Monahan and Spillane (1984), produces CO2 transfer velocities that range from 13 to 50 cm h−1 for a monthly mean. High-latitude regions of both hemispheres experience winter season means of 40 to 50 cm h−1. The global area-weighted mean CO2 transfer velocity is 19.2 cm h−1, in reasonable agreement with the 14C estimate of Broecker and Peng (1974). Although consistent with global 14C estimates, the initial version of the model predicts a factor of 2 to 3 higher CO2 transfer velocities over areas with low wind speeds relative to the parameterizations of Liss and Merlivat (1986) and Tans et al. (1990). New transfer velocity coefficients for whitecap and nonwhitecap areas are suggested that bring the low wind speed results into better agreement with observations and other models. The calculations described here suggests that oceanic gas exchange with the atmosphere is sensitive to thermal stability at the air-sea interface. This specific, turbulence-related geophysical forcing may account for a portion of the observed scatter in previously obtained experimental data that has been correlated with wind speed alone.

Atmospheric carbonyl sulfide exchange in bog microcosms

Abstract: Measurements of Carbonyl sulfide (OCS) fluxes were carried out on bog microcosms using chamber sampling and tunable diode laser analysis. Intact bog microcosms (vascular plants, mosses, and peat) removed ambient levels of OCS in the light and dark with rates from −2.4 to −8.1 ng S min−1 m−2. Peat and peat plus mosses emitted OCS in the light with rates of 17.4 and 10.9 ng S min−1 m−2, respectively. In the dark, the mosses apparently removed OCS at a rate equivalent to the peat emissions. A 3-D numerical tracer model using this data indicated that boreal bog ecosystems remove at most 1% of ambient OCS, not sufficient to account for an observed OCS depletion in boreal air masses.

Global biogeochemical cycling estimates with CZCS satellite data and general circulation models

Abstract: Computed geophysical fields from a 3-D general circulation model are coupled with the Coastal Zone Color Scanner (CZCS) satellite data on chlorophyll content of surface ocean waters. The CZCS satellite data on chlorophyll content of surface ocean waters are used to estimate the photochemical lability of dissolved organic matter in the surface ocean. Monthly estimates are made of the global ocean to atmosphere flux of a biogeochemically important gas, carbonyl sulfide (OCS), with 2.8[degree] [times] 2.8[degree] latitude-longitude spatial resolution. This novel technique provides a conceptual and computational method for integrating data collected as part of future satellite measurement campaigns, such as the Earth Observing System (EOS) and Sea-viewing Wide-field-of view Sensor (SeaWiFS), with 3-D chemistry-climate prediction models. 15 refs., 2 figs.