Diurnal cycle of summertime precipitation from NLDAS data products
The North American Land Data Assimilation System (NLDAS) produces quality-controlled and spatially and temporally consistent data sets from the best available observations and model data sets. NLDAS forcing data (Cosgrove et al., 2003) are used to drive land-surface models (LSMs) to produce model output data; the forcing data and model outputs are then used to support modeling activities. NLDAS Phase 2 (NLDAS-2) data, covering the period from January 1979 to present, are available hourly over the conterminous United States and parts of Canada and Mexico. The forcing data are assimilations of the surface states from an atmospheric reanalysis, combined with observations from GOES satellites and various precipitation sources. A daily gauge analysis of precipitation is temporally disaggregated to hourly time steps, using Stage II Doppler radar-estimated precipitation, CMORPH satellite-retrieved precipitation, HPD (hourly precipitation data set) gauge-measured precipitation, and model reanalyses.
The Modern Era Retrospective-analysis for Research and Applications (MERRA) was developed to support NASA's Earth science objectives, by applying the state-of-the-art Global Modeling and Assimilation Office (GMAO) data assimilation system that includes many modern observing systems (such as EOS) in a climate framework. The MERRA project supports NASA's Earth science interests by (1) utilizing the NASA global data assimilation system to produce a long-term (1979-present) synthesis that places the current suite of research satellite observations in a climate data context and (2) providing the science and applications communities with state-of-the-art global analyses, with emphasis on improved estimates of the hydrological cycle on a broad range of weather and climate time scales.
Diurnal cycles of summertime rainfall rates are examined over the conterminous United States (Matsui et al., 2010), using a 10-year climatology (1998-2007) of radar-gauge assimilated hourly rainfall data from NLDAS-2. As in earlier studies (e.g., Carbone et al., 2002), rainfall diurnal composites (Figure 1) show a dramatic but gradual change of the diurnal peak of precipitation from the Rocky Mountains (early afternoon) to the Great Plains (early morning). Well-defined regions of rainfall propagation over the Great Plains are identified, as well as an afternoon maximum area over the southern and eastern portions of the United States (Figure 2). Zonal phase speeds of rainfall in three different small domains are estimated, and rainfall propagation speeds are compared with background zonal wind speeds from MERRA (shown in Matsui et al., 2010). These results, based on the best available rainfall data, substantiate previous pioneering works and should be a useful benchmark for evaluating diurnal precipitation processes in high-resolution, numerical weather and climate simulations.
Figure 1. 10-year June-July-August climatology of (a) diurnal amplitude [mm/hr] (diurnal maximum minus minimum) of rainfall rate, (b) local solar time (LST) [hour] of diurnal maxima, and (c) LST of diurnal minima. The four boxes (I, II, III, and IV) correspond to the areas depicted in Figure 2.
Figure 2. Hovmöller diagrams of rainfall rate [mm/hr] from NLDAS-2 precipitation data in Areas I (43°N~46°N), II (40°N~43°N), III (37°N~40°N), and IV (34°N~37°N). The UTC time is on the left axis, with time increasing from top to bottom; the longitude on the bottom axis goes from west to east (left to right). The solid lines suggest the presence of rainfall propagation. [Figure from Matsui et al., 2010]
NLDAS Phase 2 (NLDAS-2) data are available hourly and extend from January 1979 to present. The NLDAS-2 forcing data set used is an assimilation of available observations and reanalyses. The MERRA atmospheric reanalysis data are also available from January 1979 and are available globally. Both NLDAS and MERRA data sets are available through the GES DISC interface.
Bosilovich, M., S.D. Schubert, G. Kim, R. Gelaro, M. Rienecker, M. Suarez, and R. Todling, 2006: NASA’s Modern Era Retrospective-analysis for Research and Applications (MERRA). U.S. CLIVAR Variations, 4, 5-8.
Carbone, R.E., J.D. Tuttle, D.A. Ahijevych, and S.B. Trier, 2002: Inferences of predictability associated with warm season precipitation episodes. J. Atmos. Sci., 59, 2033-2056.
Cosgrove, B.A., D. Lohmann, K.E. Mitchell, P.R. Houser, E.F. Wood, J.C. Schaake, A. Robock, C. Marshall, J. Sheffield, Q. Duan, L. Luo, R.W. Higgins, R.T. Pinker, J.D. Tarpley, and J. Meng, 2003: Real-time and retrospective forcing in the North American Land Data Assimilation System (NLDAS) project. J. Geophys. Res., 108(D22), 8842, doi:10.1029/2002JD003118.
Matsui, T., D. Mocko, M.-I. Lee, W.-K. Tao, M. J. Suarez, and R. A. Pielke Sr. (2010), Ten-year climatology of summertime diurnal rainfall rate over the conterminous U.S., Geophys. Res. Lett., 37, L13807, doi:10.1029/2010GL044139.
This work was supported by the NASA Modeling Analysis and Prediction (MAP) program. The authors are grateful to Dr. D. Considine at NASA HQ. NLDAS is a collaboration project among several groups: NOAA/NCEP's Environmental Modeling Center (EMC), NASA's Goddard Space Flight Center (GSFC), Princeton University, the University of Washington, the NOAA/NWS Office of Hydrological Development (OHD), and the NOAA/NCEP Climate Prediction Center (CPC). NLDAS is a core project with support from NOAA's Climate Prediction Program for the Americas (CPPA). MERRA is funded by the NASA MAP program and by a NASA Cooperative Agreement Notice (CAN): Earth Science REASoN - Research, Education, and Applications Solutions Network.
NLDAS data at the GES DISC: http://disc.sci.gsfc.nasa.gov/hydrology/data-holdings
MERRA data at the GES DISC: http://disc.sci.gsfc.nasa.gov/mdisc/data-holdings