7km GEOS-5 Nature Run Realism of Global Energy Budget and Land-Surface Features
In this snapshot, the realism of the GEOS-5 Nature Run (NR) long term energy budget and low-level atmospheric temperatures over land are tested by comparison to independent estimates. In addition to being directly relevant to applications of the NR simulated energy fields, these comparisons also provide a useful diagnostic for the realism of the physical processes modeled by the Nature Run, including the land surface processes, and the atmospheric processes that interact with the land surface.
The NR is a two-year free-running simulation, nominally covering 2005-2006. Since the atmosphere is chaotic, without atmospheric data assimilation the free-running NR atmosphere will quickly depart from the observed atmosphere. Hence the NR is not expected to simulate specific weather events that occurred during the nominal simulation period, and its evaluation has subsequently been focused on the prediction of typical weather events, and the simulation of a realistic climate.
In the two comparisons presented here, two-year averages from the NR are evaluated against averages from 10 years of independent observations. Note that some discrepancy is expected due to the differing temporal coverage.
The Global Annual Energy Budget:
The NEWS global annual energy budget approximately covers the 2000 – 2009, and is based on satellite observations, complemented by model products where necessary. The NEWS estimates are derived from a sophisticated multi-data merger, in which observations for the individual terms are adjusted to satisfy the energy and water balance while accounting for the uncertainty in each term. For further details, see L’Ecuyer et al [2014]. The estimates are global averages, including land and ocean.
The finding that the NR outgoing solar radiation exceeds that from NEWS is consistent with other observations indicating that the NR clouds are too bright. A breakdown of the energy budget over land and ocean shows that the larger NR global mean evaporation is due to the NR having larger evaporation from the ocean. There is also other evidence possibly supporting the over-active NR hydrological cycle suggested by the larger NR evaporation and precipitation.
2m Air Temperatures over Land
The European Center for Medium Range Weather Forecasting ERA-Interim reanalysis includes a land surface analysis which adjusts the model land surface state variables to reduce errors in the modeled 2m temperature and relative humidity. Hence, the ERA-I 2 m air temperatures (T2m) over land are expected to be reasonably accurate, at least in regions that are well sampled by T2m observations. Hence, ERA-I was used to evaluate the NR T2, with generally encouraging results. However, in Dec-Jan-Feb it is noted that there are some large regional differences. In particular, the NR T2m is cooler than ERA-I over much of north Africa, and coastal north America, while it is warmer than the ERA-I in the high northern latitudes. In the latter case, the difference can exceed 10 K, and is associated with differences in the two system's cloud cover, likely associated with problems in the cloud cover in both systems.
References
Dee, D. P., Uppala, S. M., Simmons, A. J., Berrisford, P., Poli, P., Kobayashi, S., Andrae, U., Balmaseda, M. A., Balsamo, G., Bauer, P., Bechtold, P., Beljaars, A. C. M., van de Berg, L., Bidlot, J., Bormann, N., Delsol, C., Dragani, R., Fuentes, M., Geer, A. J., Haimberger, L., Healy, S. B., Hersbach, H., Hólm, E. V., Isaksen, L., Kållberg, P., Köhler, M., Matricardi, M., McNally, A. P., Monge-Sanz, B. M., Morcrette, J.-J., Park, B.-K., Peubey, C., de Rosnay, P., Tavolato, C., Thépaut, J.-N. and Vitart, F. (2011), The ERA-Interim reanalysis: configuration and performance of the data assimilation system. Q.J.R. Meteorol. Soc., 137: 553–597. doi: 10.1002/qj.828
L'Ecuyer, T. S., H. Beaudoing, M. Rodell, W. Olson, B. Lin, S. Kato, C. A. Clayson, E. Wood, J. Sheffield, R. Adler, G. Huffman, M. Bosilovich, G. Gu, F. Robertson, P. R. Houser, D. Chambers, J. S. Famiglietti, E. Fetzer, W. T. Liu, X. Gao, C. A. Schlosser, E. Clark, D. P. Lettenmaier, K. Hilburn, 2014: Observed State of the Energy Budget in the Early 21st Century, Submitted to J. Climate.
