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Publication Date

2008-01-01

Availability

UM campus only

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Meteorology and Physical Oceanography (Marine)

Date of Defense

2008-03-25

First Committee Member

Dr. Brian Mapes - Committee Chair

Second Committee Member

Dr. Bruce Albrecht - Committee Member

Third Committee Member

Dr. David Lawrence - Outside Committee Member

Abstract

Improving diurnal errors in surface-based heating processes in models might be a promising step towards improved seasonal simulation of the North American Monsoon (NAM). This study isolates model errors in the surface energy budget and examines diurnal heating implications for seasonal development of the NAM 500hPa anticyclone and 850-500hPa thickness ridge using observations and multi-model output. Field data from the 2004 North American Monsoon Experiment (NAME) and satellite estimates are used to evaluate land-atmosphere interactions in regional and global models as part of the North American Monsoon Model Assessment Project 2 (NAMAP2). Several key findings about heating in the NAM emerge: ? Models exhibit considerable differences in surface radiation of the NAM, beginning with albedo (Fig. 3.1). All models have highly-biased albedo throughout summer (Fig. 3.2). ? Observed net surface radiation is around 125 Wm-2 over land in the NAM region in summer (Table 3.5). Models overestimate it by an average of about 20 Wm-2, despite their high albedo, apparently due to deficiencies in cloud radiative forcing. ? Partitioning of this net radiation into latent and sensible fluxes to the atmosphere differs substantially among models. Sensitivity of this partitioning to rainfall also varies widely among models, and appears clearly excessive in some models relative to observations (Fig. 4.10). ? Total sensible heating exceeds latent heating in the NAM (Table 4.1), since it covers a much larger area than the rainy core region (Fig. 4.11). ? Inter-model differences in sensible heating can be traced consistently from surface heat flux (Table 5.1), to PBL diurnal evolution (Fig. 5.1), to diurnal thickening of the lower troposphere (Fig. 5.2). ? Seasonal biases in the NAM?s synoptic structure correspond well to diurnal heating biases (Fig. 5.3, Fig. 5.5), suggesting that diurnal cycle studies from a single field season may suffice to inform physical process improvements that could impact seasonal simulation and forecasting. These NAMAP2 results highlight the range of uncertainty and errors in contemporary models, including those defining US national weather forecasting capability. Model experimentation will be necessary to fully interpret the lessons and harvest the fruits of this offline inter-comparison exercise.

Keywords

Model Inter-comparison; Seasonal Anticyclone; Diurnal Heating Errors; Surface Climate Processes; NAMAP2 Evaluation

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