HR: 0830h
AN: C41B-0964    [PDF]
TI: Improving the Snowmelt Simulation in NCEP Noah LSM
AU: * Wei, H
EM: helin.wei@noaa.gov
AF: NOAA/NCEP/EMC, 5200 Auth Rd, Camp Springs, MD 20746 United States
AB: Snowmelt is one of the most important cold-season land processes, because snowmelt strongly links surface thermal dynamics and hydrological processes. Accurately predicting the timing of snowmelt is critical for determination of the land-surface budgets of energy and water, though it is very difficult and challenging. An early bias in spring snowmelt was found to be a common problem for the NCEP Noah LSM in several uncoupled experiments (North American Land Data Assimilation System (NLDAS), PILPS-2d, PILPS-2e, and Rhone/GLASS), owing mainly to the albedo over snow cover being too low during this transient period. In the present study, through rerunning the Noah LSM for the PILPS-2d experiment, it is found that the low albedo bias during snowmelt is mainly caused by 1) an overly small snowdepth threshold (water equivalent) in the function relating snow cover fraction to snowdepth, and 2) lack of temporal resolution of vegetation greenness, which is one of the major factors to determine snow albedo in the original algorithm of the Noah LSM. After modifying both of these two factors, the snow albedo formulation as well as snowmelt timing has been improved significantly in PILPS-2d. Because PILPS-2d is only one site experiment, we will rerun 1-3 cold seasons of the retrospective NLDAS with the latest version of the Noah LSM, including aforementioned revised snow albedo formula plus some other upgrades such as albedo diurnal adjustment and patchy snow treatment of evaporation to verify that the same improvement of snowmelt timing can be extended to continental scales. The operational NESDIS daily N. Hemisphere 23-km snow cover analysis will be used to verify the control and experimental executions of the Noah LSM in the retrospective NLDAS.
DE: 1827 Glaciology (1863)
DE: 1863 Snow and ice (1827)
DE: 3322 Land/atmosphere interactions
SC: Cryosphere [C]
MN: 2003 Fall Meeting