Computation of Air-sea fluxes in Atmospheric Rivers over the Northeast Pacific using Dropsonde Observations

Abstract:

Atmospheric Rivers (AR’s) play a dominant role in variability of precipitation on the US W. Coast. A major AR study field effort with three research aircraft and the ship RV Ron Brown was conducted in January–February 2015. In this paper we report on analysis of air-sea fluxes computed from near-surface gradients in dropsonde profiles. The method was developed after a deployment of the NOAA G-4 aircraft in 2014 to evaluate observation strategies. The sonde profiles yield gradients of wind speed, potential temperature, and water vapor mixing ratio in the surface layer over the ocean. Surface fluxes can be estimated from these gradients. If sea surface temperature (SST) is available, fluxes can also be computed using a bulk-flux algorithm. Conventional atmospheric sondes do not measure SST, but we developed a method to estimate SST by extrapolating the gradient to the surface. This was effective for temperature and water vapor profiles. A short iteration yielded reasonable estimates of SST and fluxes of momentum, sensible, and latent heat. Based on the 2014 study, uncertainty in a SST estimate is about 0.10 C (std 0.5 C). Here, we will report on results from 12 G-4 missions and 7 P-3 missions from CALWATER2-2015. The P-3 missions included AXBT SST measurements for further comparison.