Evaluation of HOAPS-3 Ocean Surface Freshwater Flux Components

Abstract

Today, latent heat flux and precipitation over the global ocean surface can be determined from microwave satellite data as a basis for estimating the related fields of the ocean surface freshwater flux. The Hamburg Ocean Atmosphere Parameters and Fluxes from Satellite Data (HOAPS) is the only generally available satellite-based dataset with consistently derived global fields of both evaporation and precipitation and hence of freshwater flux for the period 1987-2005. This paper presents a comparison of the evaporation E, precipitation P, and the resulting freshwater flux E 2 P in HOAPS with recently available reference datasets from reanalysis and other satellite observation projects as well as in situ ship measurements. In addition, the humidity and wind speed input parameters for the evaporation are examined to identify sources for differences between the datasets. Results show that the general climatological patterns are reproduced by all datasets. Global mean time series often agree within about 10% of the individual products, while locally larger deviations may be found for all parameters. HOAPS often agrees better with the other satellite-derived datasets than with the in situ or the reanalysis data. The agreement usually improves in regions of good in situ sampling statistics. The biggest deviations of the evaporation parameter result from differences in the nearsurface humidity estimates. The precipitation datasets exhibit large differences in highly variable regimes with the largest absolute differences in the ITCZ and the largest relative biases in the extratropical storm-track regions. The resulting freshwater flux estimates exhibit distinct differences in terms of global averages as well as regional biases. In comparison with long-term mean global river runoff data, the ocean surface freshwater balance is not closed by any of the compared fields. The datasets exhibit a positive bias in E 2 P of 0.2-0.5 mm day 21 , which is on the order of 10% of the evaporation and precipitation estimates.* Current affiliation:

Simulated climate variability in the region of Rapa Nui during the last millennium

“…To assess the uncertainty, Andersson et al (2011) compare the precipitation climatology of HOAPS-3 with other climatologies like the atmospheric reanalysis dataset ERA-INTERIM, the satellite-derived product GPCP V2 and the TRMM 3B43 product. Around Rapa Nui, the ERA-INTERIM precipitation climatology is ∼0.12 mm d −1 (6 %) higher compared to HOAPS-3 precipitation while TRMM 3B43 (GPCP V2) precipitation is ∼0.36 mm d −1 or 18 % (∼0.14 mm/d or 7%) lower.…”

HOAPS and ERA-Interim precipitation over the sea: validation against shipboard in situ measurements

“…However, the progress in satellite technology has provided the possibility of retrieving global data sets from space, including precipitation. In addition to the Hamburg Ocean Atmosphere Parameters and Fluxes from Satellite data (HOAPS, Andersson et al, 2010Andersson et al, , 2011, remote-sensing-based precipitation data sets are alternatively available, e.g. from the GPCP (Global Precipi-overestimation of 8 to 10 %.…”

“…Note that these comparisons were done against measurements on atolls, although the representativeness of the atoll gauges of open-ocean rainfall is still an unanswered question (Wang et al, 2014). Andersson et al (2011) have shown that HOAPS gives lower precipitation rates than ERA-Interim, except for small areas in the northern subtropics, the north-western and south-western Atlantic Ocean. They also figured out that over the mid-high latitudes between 40 and 70 • , the precipitation (only liquid precipitation) in GPCP (Adler et al, 2003) is also systematically 10-30 % higher relative to HOAPS.…”

Uncertainty Characterization of HOAPS-3.3 Latent Heat Flux Related Parameters

“…According to Andersson et al (2011), the E-P budget of HOAPS-3.2 is not closed. This also accounts for HOAPS-3.3, with below the HOAPS-3.2 estimate and can be evaluated as an improvement towards closing the global freshwater flux imbalance.…”

“…The usefulness of the HOAPS climatology for climatological applications has been tested among numerous intercomparison studies and promising results have been published within Bentamy et al (2003), Bourras (2006), Klepp et al (2008), Winterfeldt et al (2010), Andersson et al (2011), andStendardo et al (2016). In the framework of assessing sea surface freshwater fluxes, Romanova et al (2010) for example 25 conclude that HOAPS-3 is well suited for global applications and serves as an important and independent data set that should be included in future ocean synthesis.…”