The Reliability of Antarctic Tropospheric Pressure and Temperature in the Latest Global Reanalyses

Abstract

In this study, surface and radiosonde data from staffed Antarctic observation stations are compared to output from five reanalyses [Climate Forecast System Reanalysis (CFSR), 40-yr ECMWF Re-Analysis (ERA-40), ECMWF Interim Re-Analysis (ERA-Interim), Japanese 25-year Reanalysis (JRA-25), and Modern Era Retrospective-Analysis for Research and Applications (MERRA)] over three decades spanning . Bias and year-to-year correlation between the reanalyses and observations are assessed for four variables: mean sea level pressure (MSLP), near-surface air temperature (T s ), 500-hPa geopotential height (H 500 ), and 500-hPa temperature (T 500 ).It was found that CFSR and MERRA are of a sufficiently high resolution for the height of the orography to be accurately reproduced at coastal observation stations. Progressively larger negative T s biases at these coastal stations are apparent for reanalyses in order of decreasing resolution. However, orography height bias cannot explain large winter warm biases in CFSR, JRA-25, and MERRA (11.18, 10.28, and 7.98C, respectively) at Amundsen-Scott and Vostok, which have been linked to problems with representing the surface energy balance.Linear trends in the annual-mean T 500 and H 500 averaged over Antarctica as a whole were found to be most reliable in CFSR, ERA-Interim, and MERRA, none of which show significant trends over the period 1979-2008. In contrast JRA-25 shows significant negative trends over 1979-2008 and ERA-40 gives significant positive trends during the 1980s (evident in both T 500 and H 500 ). Comparison to observations indicates that the positive trend in ERA-40 is spurious. At the smaller spatial scale of individual stations all five reanalyses have some spurious trends. However, ERA-Interim was found to be the most reliable for MSLP and H 500 trends at station locations.

Temperature and Wind Climate of the Antarctic Peninsula as Simulated by a High-Resolution Regional Atmospheric Climate Model

“…15b,d) and the SCAR-READER stations (Fig. 4) and have been previously reported using lower-resolution datasets (Bromwich 2004;Bracegirdle and Marshall 2012). However, the significant warming for the southwestern AP ice sheet in the low-resolution ERA-Interim dataset is not seen at 5.5 km, which rather shows a cooling.…”

“…To fill these gaps, remote sensing techniques can be used, such as microwave sensors to detect (brightness) temperatures (Tedesco et al 2007) or radar backscatter to identify melt episodes (Barrand et al 2013). Atmospheric reanalysis products (Bracegirdle and Marshall 2012) and global climate models (GCMs) provide gridded climate information, but with horizontal resolutions that range from 25 to 150 km, these do not accurately resolve the rough topography of the AP. Dynamical downscaling using high-resolution regional atmospheric climate models (RCMs) has proven to be a good method to represent climate at 5-10-km resolution.…”

The Influence of the Amundsen–Bellingshausen Seas Low on the Climate of West Antarctica and Its Representation in Coupled Climate Model Simulations

“…For this reason we only concentrate on SAT biases over land, which, as we show, appear to respond more in line with the representation of the circulation. We further note that Bracegirdle and Marshall (2012) show that ERA-Interim is itself characterized by a cold bias of a few degrees when compared to coastal stations (which they attribute to orography height errors associated with coarse resolution), while, as its SIE field is based on daily observations, it is representative of actual conditions. Figure 10 and Table 1 shows that CSIRO-Mk3.6.0 is the worst-performing model examined in terms of the representation of longitudinal position, with Fig.…”

“…ERAInterim was produced using the ECMWF Integrated Forecast System with a horizontal resolution of T255 (N128, ;80-km grid spacing), 60 vertical levels, and a model top of 0.1 hPa. Observations were assimilated using a 12-h four-dimensional variational analysis with output every 6 h. In a recent study, Bracegirdle and Marshall (2012) determined that ERA-Interim was the most accurate of six different reanalysis datasets when verified over Antarctica against independent surface and midtropospheric pressure and temperature in situ observations, including buoy data from the Bellingshausen Sea. All calculations used data obtained at a horizontal resolution of T159 (N80, ;125-km grid spacing).…”

The impacts of El Niño on the observed sea ice budget of West Antarctica

“…ERA-Interim was found to be the most reliable reanalysis product over Antarctica by Bracegirdle and Marshall [2012], and has been used in recent studies examining the influence of near-surface winds on sea ice [Holland and Kwok, 2012;Holland, 2014]. The 850 hPa temperature was chosen (instead of surface temperature) to minimize the influence of observed sea ice, which is used as a lower boundary condition within the ERA-Interim reanalysis.…”