Validation of eight atmospheric reanalyses in the Antarctic Peninsula region

Abstract

Eight atmospheric reanalyses were compared against observed vertical profiles of temperature, specific humidity and wind speed collected by two research aircraft in February-March 2010 in the Antarctic Peninsula region. These data offered a rare possibility to validate reanalyses against independent in-situ data which have not been assimilated into the reanalyses. The reanalyses had generally too moist profiles with too low wind speeds, but otherwise the errors in the reanalyses had large spatial differences. On the eastern side of the peninsula, the near-surface temperatures were largely overestimated. None of the reanalysis outperformed the others in all variables, at all altitudes and on both sides of the peninsula. Generally, NCEP-CFSR and MERRA had the smallest errors in temperature profiles, JRA-55 had marginally the most accurate specific humidity profiles and NCEP-CFSR had the best wind profiles. The reanalyses were coherent, although biased, on the western side of the Antarctic Peninsula, but on the eastern side the spread was large. All the reanalyses underestimated the variability between the individual profiles of temperature and wind speed. The modern reanalyses with a sufficient spatial resolution and an adequate data assimilation method outperformed the others, especially on the eastern side.

Assessment of Atmospheric Reanalyses With Independent Observations in the Weddell Sea, the Antarctic

“…However, ERA-Interim does suffer from some prominent biases, including a significant warm bias of up to +1.4 K compared with the Aranda soundings. This low-level warm bias in ERA-Interim is consistent with findings in more recent data from the eastern side of the Antarctic peninsula (Nygård et al, 2016) and also with data from the Arctic Jakobson et al, 2012;Liu et al, 2008;Lüpkes et al, 2010;Wesslén et al, 2014). Corresponding to this warm bias, there is a significant moist bias in the lowermost layers of the reanalyses, when compared against the Aranda soundings and, to a lesser degree, the Fedorov soundings.…”

The Transient Response of Southern Ocean Circulation to Geothermal Heating in a Global Climate Model

“…Here we show that geothermal heating-induced anomalies do extend toward the surface (thus impacting surface water mass transformation), particularly in polar regions where approximated atmospheric forcing errors can be substantial (e.g., Nygard et al 2016;Hobbs et al 2016). In an ocean-ice model, the approximated forcing components have their own errors distinct from the model that can enhance or compete with the model errors, with no clear way to separate the two error types (cf.…”

A New Method to Evaluate Reanalyses Using Synoptic Patterns: An Example Application in the Ross Sea/Ross Ice Shelf Region

“…In terms of specific weaknesses a number of studies have identified spurious trends in reanalyses in the temperature (Huai et al, ; Wang et al, ; Zhang et al, ), pressure (Bromwich & Fogt, ; Schneider & Fogt, ), precipitation (Bromwich et al, ; Nicolas & Bromwich, ), and surface wind (Bromwich et al, ; Nygard et al, ) fields around the Antarctic. Wohland et al () also questioned the quality of reanalyses surface wind trends in centennial reanalyses and Thorne and Vose () have questioned the reliability of long‐term trends in atmospheric reanalyses more widely.…”

“…Though they also see a lower wind variability in the reanalyses relative to AWS data which they attribute to smoothed topography. Nygard et al () examined eight reanalyses around the Antarctic Peninsula relative to field observations and found that wind speeds were predominantly low biased. Work in Jones et al () compared AWS wind speeds to four reanalysis products in the Amundsen Sea Embayment.…”