The Influences of TOVS Radiance Assimilation on Temperature and Moisture Tendencies in JRA-25 and ERA-40

Sakamoto, Masami; Christy, John R.

doi:10.1175/2009jtecha1193.1

Cited by 27 publications

(25 citation statements)

References 34 publications

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“…This sensitivity would explain the drop in precipitation in 1992 and its increase after 2005. As already seen over Antarctica in MERRA, the impact of AMSU is visible in global precipitation in MERRA, JRA-25, and CFSR (Onogi et al 2007;Sakamoto and Christy 2009;Saha et al 2010;Cullather and Bosilovich 2011). Further assessment of the global hydrological cycle in recent global reanalyses is given by Trenberth et al (2011).…”

Section: Precipitation Changes Over the Southern Oceanmentioning

confidence: 76%

An Assessment of Precipitation Changes over Antarctica and the Southern Ocean since 1989 in Contemporary Global Reanalyses*

2011

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This study evaluates the temporal variability of the Antarctic surface mass balance, approximated as precipitation minus evaporation (P 2 E), and Southern Ocean precipitation in five global reanalyses during 1989-2009. The datasets consist of the NCEP/U.S. Department of Energy (DOE) Atmospheric Model Intercomparison Project 2 reanalysis (NCEP-2), the Japan Meteorological Agency (JMA) 25-year Reanalysis (JRA-25), ECMWF Interim Re-Analysis (ERA-Interim), NASA Modern Era Retrospective-Analysis for Research and Application (MERRA), and the Climate Forecast System Reanalysis (CFSR). Reanalyses are known to be prone to spurious trends and inhomogeneities caused by changes in the observing system, especially in the data-sparse high southern latitudes. The period of study has seen a dramatic increase in the amount of satellite observations used for data assimilation.The large positive and statistically significant trends in mean Antarctic P 2 E and mean Southern Ocean precipitation in NCEP-2, JRA-25, and MERRA are found to be largely spurious. The origin of these artifacts varies between reanalyses. Notably, a precipitation jump in MERRA in the late 1990s coincides with the start of the assimilation of radiances from the Advanced Microwave Sounding Unit (AMSU). ERA-Interim and CFSR do not exhibit any significant trends. However, the potential impact of the assimilation of rain-affected radiances in ERA-Interim and inhomogeneities in CFSR pressure fields over Antarctica cast some doubt on the reliability of these two datasets.The authors conclude that ERA-Interim likely offers the most realistic depiction of precipitation changes in high southern latitudes during . The range of the trends in Antarctic P 2 E among the reanalyses is equivalent to 1 mm of sea level over 21 years, which highlights the improvements still needed in reanalysis simulations to better assess the contribution of Antarctica to sea level rise. Finally, this work argues for continuing cautious use of reanalysis datasets for climate change assessment.

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Section: Precipitation Changes Over the Southern Oceanmentioning

confidence: 76%

An Assessment of Precipitation Changes over Antarctica and the Southern Ocean since 1989 in Contemporary Global Reanalyses*

2011

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“…However, a clearer pattern emerges for Antarctic-wide averages. In both variables there is strong agreement between CFSR, ERA-Interim, and MERRA-none of which show significant linear trends over the period trends, respectively, which appear spurious when compared to raw Television and Infrared Observation Satellite Operational Vertical Sounder (TOVS) tendencies (Sakamoto and Christy 2009). The positive ERA-40 T 500 trend also appears spurious when taking into account observational uncertainty in the radiosonde data.…”

Section: Conclusion and Discussionmentioning

confidence: 94%

“…We investigated the observational uncertainty of the above results by assessing five additional adjusted radiosonde temperature datasets (HadAT2, IUK, RAOBCORE, RICH-obs, RICH-tau), which show that the positive ERA-40 T 500 trend (subsampled to available station data) is clearly outside the range of the different datasets (not shown). The negative JRA-25 trend is not clearly outside the range of the radiosonde datasets but should be treated with caution since the change from TOVS to the Advanced TOVS (ATOVS) in 1998 along with a coincident change in the method of assimilating radiances caused a discontinuity in stratospheric temperatures (Onogi et al 2007;Sakamoto and Christy 2009). This is partly a consequence of the relatively large stratospheric and upper-tropospheric bias in the JRA-25 forecast model (Onogi et al 2007).…”

Section: Conclusion and Discussionmentioning

confidence: 99%

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

2012

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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.

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“…A problematic issue impacts RAOBCORE and RICH and is related to a warming shift in 1991 of the upper troposphere in the ERA-40 Reanalyses on which the two datasets rely. This was shown in [19] to be likely spurious due to a mishandling of a change in an infrared channel, a diagnosis acknowledged by the ECMWF (see also ECMWF Newsletter No. 119, Spring 2009).…”

Section: Radiosondementioning

confidence: 97%

“…Analysis of wind data, which in some latitudes is very sparse, and then applying the TWE is a sensitive derivation that creates these uncertainties. Indeed, the percentages of 5° Lat by 10° Lon boxes in each 5° Lat band that contain at least one useful radiosonde time series at 200 hPa from 20°S to 40°N are only 14,8,8,6,17,19,22,22,31, 39, 33 and 56% respectively. Vast areas of the tropics and subtropics are not measured at all in this calculation where it is possible that decadal-scale circulation changes may have provided a compensating influence in unmonitored areas.…”

Section: Thermal Windmentioning

confidence: 99%

What Do Observational Datasets Say about Modeled Tropospheric Temperature Trends since 1979?

et al. 2010

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Updated tropical lower tropospheric temperature datasets covering the period 1979-2009 are presented and assessed for accuracy based upon recent publications and several analyses conducted here. We conclude that the lower tropospheric temperature (T LT ) trend over these 31 years is +0.09 ± 0.03 °C decade −1 . Given that the surface temperature (T sfc ) trends from three different groups agree extremely closely among themselves (~ +0.12 °C decade −1 ) this indicates that the -scaling ratio‖ (SR, or ratio of atmospheric trend to surface trend: T LT /T sfc ) of the observations is ~0.8 ± 0.3. This is significantly different from the average SR calculated from the IPCC AR4 model simulations which is ~1.4. This result indicates the majority of AR4 simulations tend to portray significantly greater warming in the troposphere relative to the surface than is found in observations. The SR, as an internal, normalized metric of model behavior, largely avoids the confounding influence of short-term fluctuations such as El Niños which make direct comparison of trend magnitudes less confident, even over multi-decadal periods. OPEN ACCESSRemote Sensing 2010, 2 2149

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The Influences of TOVS Radiance Assimilation on Temperature and Moisture Tendencies in JRA-25 and ERA-40

Cited by 27 publications

References 34 publications

An Assessment of Precipitation Changes over Antarctica and the Southern Ocean since 1989 in Contemporary Global Reanalyses*

An Assessment of Precipitation Changes over Antarctica and the Southern Ocean since 1989 in Contemporary Global Reanalyses*

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

What Do Observational Datasets Say about Modeled Tropospheric Temperature Trends since 1979?

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