ESSO - Indian National Centre for Ocean Information Services
(An Autonomous Body under the Ministry of Earth Sciences, Govt. of India)
Description
How are TropFlux fluxes estimated ?
- The TropFlux heat and momentum fluxes are estimated from the COARE v3 algorithm (Fairall et al. 2003), arguably one of the most suited algorithm for fluxes estimations in the tropical regions. This algorithm requests surface meteorological parameters (10m-winds, 2m-air and sea temperature, 2m-air relative humidity) and downward radiative (shortwave and infrared fluxes) as input parameters.
- The analysis of various data sources shows that, except for shortwave radiation, ERA-I data generally displays the best agreement to the Global Tropical Moored Buoy Array data, despite systematic biases and underestimated variability Praveen Kumar et al. 2012. The ISCCP provides the best shortwave data. TropFlux hence uses bias and amplitude corrected ERA-I (10m-winds, 2m-air and sea temperature, 2m-air relative humidity and downward radiative fluxes) and ISCCP (shortwave radiation) fluxes. All bias corrections are derived on the basis of comparisons with the Global Tropical Moored Buoy Array data, and are described in detail in Praveen Kumar et al. 2012.
- An additional climatological surface temperature-dependent gustiness is applied to wind speed, in order to account for unresolved (sub-daily and subgrid-scale) variability.
- Since ISCCP shortwave data is not updated on a regular basis, we provide an alternative shortwave flux estimate that is less accurate, but available until present. This estimate uses the ISCCP shortwave climatology plus anomalies that are linearly related to NOAA Outgoing Longwave Radiation anomalies with respect to the seasonal cycle. Such an estimate is almost as good as ISCCP in deep atmospheric convection regions such as the ITCZ or Indo-Pacific warm pool. It does not perform as well as ISCCP in regions of low clouds such as the eastern equatorial Pacific and Atlantic oceans, but is in any case better than most available re-analyses in those regions (Praveen Kumar et al. 2012). The net surface shortwave that is provided in TropFlux data files is based on ISCCP data over the entire period for which it is available (July 1983 to December 2009 at the time of writing), with a linear transition to OLR-derived shortwave over a three months window at the edges of the ISCCP-availability window.