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Enhanced atmospheric motion vectors (AMVs) produced from the geostationary Multifunctional Transport Satellite (MTSAT) are assimilated into the U.S. Navy Operational Global Atmospheric Prediction System (NOGAPS) to evaluate the impact of these observations on tropical cyclone track forecasts during the simultaneous western North Pacific Ocean Observing System Research and Predictability Experiment (THORPEX) Pacific Asian Regional Campaign (TPARC) and the Tropical Cyclone Structure-2008 (TCS-08) field experiments. Four-dimensional data assimilation is employed to take advantage of experimental high-resolution (space and time) AMVs produced for the field campaigns by the Cooperative Institute for Meteorological Satellite Studies. Two enhanced AMV datasets are considered: 1) extended periods produced at hourly intervals over a large western North Pacific domain using routinely available MTSAT imagery and 2) limited periods over a smaller storm-centered domain produced using special MTSAT rapid-scan imagery. Most of the locally impacted forecast cases involve Typhoons Sinlaku and Hagupit, although other storms are also examined. On average, the continuous assimilation of the hourly AMVs reduces the NOGAPS tropical cyclone track forecast errors-in particular, for forecasts longer than 72 h. It is shown that the AMVs can improve the environmental flow analyses that may be influencing the tropical cyclone tracks. Adding rapid-scan AMV observations further reduces the NOGAPS forecast errors. In addition to their benefit in traditional data assimilation, the enhanced AMVs show promise as a potential resource for advanced objective data-targeting methods. [ABSTRACT FROM AUTHOR]

Difficulty analyzing mesoscale features in California and Nevada for a 1991 case study prompted a review of techniques for sea level pressure (SLP) reduction and an evaluation of the performance of the various techniques for the U.S. west coast states at 0000 UTC 30 November 1991. The objective of any SLP reduction procedure is to provide a pressure field that portrays meteorological features rather than terrain features, a difficult goal to meet in this region given the steep terrain gradients on the western slopes of the Sierra Nevada range. The review and evaluation are performed both for techniques applicable at individual stations and for techniques applicable at grid points in a model analysis or forecast. When using station data, one would like to perform a manual or objective analysis of SLP with the greatest number of stations possible by adding stations that report only altimeter setting to the stations that report both SLP and altimeter setting. The results of the comparison show that the incorporation of altimeter-setting stations into an analysis of SLP was found to be practical only at elevations less than 300 m. Above this, the standard reduction includes empirical corrections that cannot be easily duplicated, and the other reduction techniques yielded values that varied over a large enough range that the uncertainty associated with the choice of technique becomes too great to permit the analysis of weak mesoscale features. At such low elevations, the various techniques examined gave similar results; therefore, the simple reduction is recommended. In elevated plateau regions, a pressure analysis on a geopotential surface at approximately the mean terrain height is recommended to minimize reduction errors. No satisfactory solution was found for regions with steep terrain gradients. Computing SLP from model objective analyses or forecasts that are in the model's native vertical coordinate, typically the terrain-following sigma coordinate, poses a... [ABSTRACT FROM AUTHOR]