Satellite Estimation of Air-Sea Gas Transfer During GasEx-3 Using QuikSCAT and Jason-1 Microwave Radars

The continued development of our scatterometer-based algorithm for estimating air-sea gas transfer velocity (k) from QuikSCAT normalized radar backscatter (&sigma^o) at 25 km and one day resolution will be greatly strengthened by collaboration with investigators from the GasEx-3 expedition to the Southern Ocean. To this end, we present here daily results from the current QuikSCAT transfer velocity algorithm for the time period and study area of the Southern Ocean GasEx field campaign. We encourage the field investigators of make comparisons between our backscatter-based estimates of gas transfer velocity and collaborate with us on improving this technique.

The algorithm calculates k from a field-determined, quadratic function of the small-scale wave mean square slope (). The , in turn, is calculated from an empirical function of QuikSCAT normalized radar backscatter (&sigma^o). Our algorithm is calibrated with an altimeter-based --&sigma^o relationship using co-located QuikSCAT--altimeter &sigma^o. Our proposed study has the following objectives: to (1) carry out a regional analysis of the spatial and temporal variability of k in the proposed study area, (2) provide regional near real time (order of 3-12 hr) remote-sensing estimates of k during the field campaign, (3) use GasEx-3 field measurements of k and surface roughness collected during QuikSCAT (and less frequently, Jason-1) overflights to better constrain the algorithm parameters, (4) carry out time-series and EOF analysis of the resultant gas transfer velocity fields, and (5) assimilate the resulting gas transfer velocity fields into the NCAR Community Climate Simulation Model (CCSM) Ocean General Circulation Model (OGCM) at both global and regional scales. We will compare model function parameters optimized from the field data with those derived from the altimeter-QuikSCAT match-ups in order to strengthen the calibration obtained from the co-located TOPEX and Jason-1 &sigma^o and then extend this improvement into the seven-plus years of data overlap between the three satellites. With internally consistent, field calibrated time series we will examine the seven-plus year record for evidence of trends and expressions of basin to global scale phenomena (climatic oscillation indices, e.g. ENSO, NAO, {\em etc.}). Finally, we will apply these results to the NCAR CCSM OGCM to better constrain the air-sea flux of important, radiatively active gases ({\em e.g.}, CO₂). Biogeochemical submodels of this OGCM resolve processes that influence the time scales of gas exchange on 1-2 days and at mesoscale spatial scales; consequently the space and time resolution of our algorithm is well suited for capturing potential ecosystem shifts. This study has direct relevance to NASA's Ocean Biology and Biogeochemistry program's focus on quantifying the impacts and feedbacks of physical and biological oceanographic mechanisms, particularly carbon sources and sinks at the air-sea interface. This completely new use of SeaWinds/QuikSCAT data will allow an important biogeochemical property to be developed from space-based assets beyond traditional ocean color measurements. Direct benefit to NASA will be to quantify spatial patterns and variability of potential sources and sinks of CO₂ and improve important aspects of our dynamic understanding of the global carbon cycle.