Recent changes in global oceanic latent heat flux from remote sensing

Precipitation and evaporation/Latent Heat Flux (LHF) are two important components of the global water/energy cycle. Documentation of their changes and variations is crucial for understanding the variations of the global climate. Global oceanic LHF is examined using three different remote sensing based products and National Center for Environmental Prediction (NCEP) reanalyses data. The remote sensing products are 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 of the LHF time series yield strong signals that correspond to the increase. Based on linear regression analyses, the increases are 9.4%, 13.0%, 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 oceans, 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 of NCEP LHF data has spatial patterns similar to those of GSSTF2 and HOAPS2, but the time series does not show a clear increase. The second EOF of NCEP data 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.; From balance considerations, precipitations over oceans and land are also analyzed. The land precipitation data from Global Precipitation Climatology Project show a linear increase of 9.2% from 1991 to 2000. No significant linear trend is found in oceanic precipitation for the same period, based on the Special Sensor Microwave/Imager rain rate from Polar Satellite Precipitation Data Center.