Atmospheric reanalysis

In operational numerical weather prediction, forecast models are used to predict future states of the atmosphere, based on how the climate system evolves with time from an initial state. The initial state provided as input to the forecast must consist of data values for a range of "prognostic" meteorological fields – that is, those fields which determine the future evolution of the model. Spatially varying fields are required in the form used by the model, for example at each intersection point on a regular grid of longitude and latitude circles, and initial data must be valid at a single time that corresponds to the present or the recent past. By contrast, the available observational data usually do not include all of the model's prognostic fields, and may include other additional fields; these data also have different spatial distribution from the forecast model grid, are valid over a range of times rather than a single time, and are also subject to observational error. The technique of data assimilation is therefore used to produce an analysis of the initial state, which is a best fit of the numerical model to the available data, taking into account the errors in the model and the data.

In addition to initializing operational forecasts, the analyses themselves are a valuable tool for subsequent meteorological and climatological studies. However, an operational analysis dataset, i.e. the analysis data which were used for the real-time forecasts, will typically suffer from inconsistency if it spans any extended period of time, because operational analysis systems are frequently being improved. A reanalysis project involves reprocessing observational data spanning an extended historical period using a consistent modern analysis system, to produce a dataset that can be used for meteorological and climatological studies.

Diverse studies use reanalysis data for reproducing other climatic variables by black-box models (e.g. sea state variables{{Cite journal|last=Peres|first=D. J.|last2=Iuppa|first2=C.|last3=Cavallaro|first3=L.|last4=Cancelliere|first4=A.|last5=Foti|first5=E.|date=2015-10-01|title=Significant wave height record extension by neural networks and reanalysis wind data|journal=Ocean Modelling|volume=94|pages=128–140|doi=10.1016/j.ocemod.2015.08.002|bibcode=2015OcMod..94..128P}}).

Examples of reanalysis datasets include the ECMWF re-analysis,Uppala, S., and coauthors, 2005: The ERA-40 Re-Analysis. Quart. J. Roy. Meteor. Soc., 131, 2961–3012. doi:10.1256/qj.04.176 the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2),Gelaro, R., and coauthors, 2017: The Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA-2). J. Climate, 30, 5419-5454, [https://dx.doi.org/10.1175/JCLI-D-16-0758.1] and the NCEP/NCAR Reanalysis,Kalnay, E., and coauthors, 1996: The NCEP/NCAR 40-Year Reanalysis Project. Bull. Amer. Meteor. Soc., 77, 437–471. doi:10.1175/1520-0477(1996)077%3C0437:TNYRP%3E2.0.CO;2 and the JRA-25[http://jra.kishou.go.jp/JRA-25/index_en.html JRA-25]

Onogi, K., and coauthors, 2007: The JRA-25 Reanalysis. J. Meteor. Soc. Japan, 85, 369–432. reanalysis conducted by the Japan Meteorological Agency. In addition to these global reanalysis projects, there are also high-resolution regional reanalysis activities for different regions, e.g. for North America,Mesinger, F. and coauthors, 2006, North American Regional Reanalysis. Bull. Amer. Meteor. Soc. doi:10.1175/BAMS-87-3-343 EuropeBollmeyer, C., Keller, J. D., Ohlwein, C., Wahl, S., Crewell, S., Friederichs, P., Hense, A., Keune, J., Kneifel, S., Pscheidt, I., Redl, S., and Steinke, S.: Towards a high-resolution regional reanalysis for the European CORDEX domain, Q. J. R. Meteorol. Soc., 141, 1–15, 2015, doi:10.1002/qj.2486 or Australia.Su, C.-H., Eizenberg, N., Steinle, P., Jakob, D., Fox-Hughes, P., White, C. J., Rennie, S., Franklin, C., Dharssi, I., and Zhu, H., 2019: BARRA v1.0: the Bureau of Meteorology Atmospheric high-resolution Regional Reanalysis for Australia, Geosci. Model Dev., 12, 2049-2068, doi:10.5194/gmd-12-2049-2019 Such regional reanalyses are typically based on a regional weather forecasting model and use boundary conditions from a global reanalysis.Kaiser-Weiss, A. K., Borsche, M., Niermann, D., Kaspar, F. Lussana, C., Isotta, F., van den Besselaar, E., van der Schrier, G., and Undén, P.: Added value of regional reanalyses for climatological applications, Environmental Research Communications, 2019. DOI:10.1088/2515-7620/ab2ec3

{{excerpt|ECMWF re-analysis}}

{{excerpt|NCEP/NCAR Reanalysis}}

While often reanalysis can be thought as the best estimate on many variables (such as windsKaiser-Weiss, A. K., Kaspar, F., Heene, V., Borsche, M., Tan, D. G. H., Poli, P., Obregon, A., and Gregow, H., 2015: Comparison of regional and global reanalysis near-surface winds with station observations over Germany, Adv. Sci. Res., 12, 187-198, doi:10.5194/asr-12-187-2015 and temperature) of the atmosphere, its usage must be taken with caution.Parker, W.S., 2016: Reanalyses and Observations: What’s the Difference? Bull. Amer. Meteor. Soc., 97, 1565–1572, doi:10.1175/BAMS-D-14-00226.1 Degradation, replacement, or modification of instruments (e.g. satellites), as well as changes in methods of observation (e.g., surface, aloft) may create error.Trenberth, K. E., D. P. Stepaniak, J. W. Hurrell, and M. Fiorino, 2001: Quality of Reanalyses in the Tropics. J. Climate, 14, 1499–1510. doi:10.1175/1520-0442(2001)014%3C1499:QORITT%3E2.0.CO;2 Not all reanalysis data are constrained by observation: some data types, such as precipitation (depending on the reanalysis) and surface evapotranspiration (for which global observations simply do not exist), are obtained by running (presumably newer) general circulation or NWP models. Reanalyses are known not to conserve moisture.Nigam, S., and A. Ruiz-Barradas, 2006: Seasonal Hydroclimate Variability over North America in Global and Regional Reanalyses and AMIP Simulations: Varied Representation. J. Climate, 19, 815–837. doi:10.1175/JCLI3635.1

{{reflist|2}}

• Kalnay, E., and coauthors, 1996: The NCEP/NCAR 40-Year Reanalysis Project. Bull. Amer. Meteor. Soc., 77, 437–471.
• Kanamitsu, M., W. Ebisuzaki, J. Woolen, S.-K. Yang, J. J. Hnilo, M. Fiorino, and G. L. Potter, 2002: NCEP-DOE AMIP-II Reanalysis (R-2). Bull. Amer. Meteor. Soc., 83, 1631–1643.
• Mesinger, F., and coauthors, 2006: North American Regional Reanalysis. Bull. Amer. Meteor. Soc., 87, 343–360, http://dx.doi.org/10.1175/BAMS-87-3-343.
• Uppala, S., and coauthors, 2005: The ERA-40 Re-Analysis. Quart. J. Roy. Meteor. Soc., 131, 2961–3012, https://doi.org/10.1256/qj.04.176.
• Hersbach, H., Bell, B., Berrisford, P., Hirahara, S., Horányi, A., Muñoz-Sabater, J., Nicolas, J., Peubey, C., Radu, R., Schepers, D., Simmons, A., Soci, C., Abdalla, S., Abellan, X., Balsamo, G., Bechtold, P., Biavati, G., Bidlot, J., Bonavita, M., De Chiara, G., Dahlgren, P., Dee, D., Diamantakis, M., Dragani, R., Flemming, J., Forbes, R., Fuentes, M., Geer, A., Haimberger, L., Healy, S., Hogan, R. J., Hólm, E. A., Janisková, M., Keeley, S., Laloyaux, P., Lopez, P., Radnoti, G., Rosnay, P. D., Rozum, I., Vamborg, F., Villaume, S., Thépaut, J.-N., 2020: The ERA5 global reanalysis. Q J R Meteorol Soc, https://doi.org/10.1002/qj.3803.
• Onogi, K., and coauthors, 2007: The JRA-25 Reanalysis. J. Meteor. Soc. Japan, 85, 369–432, https://doi.org/10.2151/jmsj.85.369.
• Kaspar, F., Niermann, D., Borsche, M., Fiedler, S., Keller, J., Potthast, R., Rösch, T., Spangehl, T., and Tinz, B., 2020: Regional atmospheric reanalysis activities at Deutscher Wetterdienst: review of evaluation results and application examples with a focus on renewable energy, Adv. Sci. Res., 17, 115–128, https://doi.org/10.5194/asr-17-115-2020.
• Khatibi, A.; Krauter, S. Validation and Performance of Satellite Meteorological Dataset MERRA-2 for Solar and Wind Applications. Energies 2021, 14, 882. https://doi.org/10.3390/en14040882

• Ocean reanalysis

• [https://web.archive.org/web/20100327155757/http://www.ecmwf.int/newsevents/training/lecture_notes/LN_DA.html lecture notes] from the European Centre for Medium-Range Weather Forecasts
• [https://reanalyses.org/atmosphere/comparison-table Atmospheric Reanalyses Comparison Table] from [https://reanalyses.org Reanalysis.org]

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