Increase in global oceanic latent flux: results from remote sensing and NCEP reanalyses

Global oceanic Latent Heat Flux (LHF) is examined using three different remote sensing based products and NCEP reanalysis data. The remote sensing products include the Goddard Satellite Surface Turbulence/Flux version 2 (GSSTF2), the Japanese Ocean Flux Data Set with Use of Remote Sensing Observations (J-OFURO) and the Hamburg Ocean Atmosphere Parameters and Fluxes from Satellite Data version 2 (HOAPS2). An increase in global average LHF over the period 1992 to 2000 can be observed in all the data sets. Both wavelet and Empirical Mode Decomposition (EMD) of the LHF time series yield strong signals that correspond to the increase. Based on linear regression analyses, the increases are 9.4%, 13.05%, 7.3%, and 3.9% for GSSTF2, J-OFURO, HOAPS2 and NCEP, respectively. Analysis of the remote sensing data in different zonal bands shows that the increase occurs mainly over 40°S to 40°N. EOF analyses are performed on these data sets. The first EOF of both GSSTF2 and HOAPS2 is characterized by positive values over most of the area, with negative values over a small area at eastern equatorial Pacific. The associated time series show a monotonic increase from 1992 to 2000. Therefore the first EOF of GSSTF2 and HOAPS2 is interpreted as an increasing mode, which is not found in J-OFURO. This mode is consistent with other satellite observations of an enhanced Hadley circulation. The second EOF of all three remote sensing data sets is an ENSO mode, the correlation between the time series and an SOI are 0.74, 0.71 and 0.59 for GSSTF2, J-OFURO, and HOAPS2, respectively. The first EOF pattern of NCEP is similar to those derived from remote sensing, but the time series does not show a clear increase. The second EOF of NCEP reanalyses is an ENSO mode. The correlation between the time series and SOI is 0.61. Potential error sources of the remote sensing data sets are discussed in order to provide uncertainty estimates for these huge increases in LHF.