**Evaluation of the Utility of Satellite-Derived Integrated Water Vapor\
and Wind Vector Data Within THORPEX**

Progress report for FY2007

Gary Wick, NOAA/ESRL/PSD2

Our activities in this first year of research focused on two primary
objectives:

-   Evaluating of the ability of models to reproduce the magnitude and
    transport of water vapor and the magnitude and direction of surface
    winds, and

-   Utilizing direct IWV observations to understand the characteristics
    of atmospheric rivers and their impact on forecasts for the West
    Coast of the US.

The specific tasks completed in support of these objectives included
creation of 6- and12-hourly data sets of Special Sensor Microwave Imager
(SSM/I)-derived integrated water vapor (IWV) content over the Pacific
Ocean, development of a climatology of landfalling atmospheric rivers,
initiation of automated atmospheric river detection and characterization
techniques, and initiation of comparisons of the representation of IWV
among observations and members of the THORPEX Interactive Grand Global
Ensemble (TIGGE). Additional details on each of these tasks are included
in the following paragraphs.

To enable characterization of atmospheric river and winter storm events
as well as the validation of forecast fields both from TIGGE and the
activities of Jian-Wen Bao from PSD, it was necessary to first compile
grids of the observed IWV content. Grids at both 6- and 12-hourly
resolution were derived from SSM/I data using multiple retrieval
algorithms for the period from 1997 to the present. Two newer algorithms
were implemented to support this work. Techniques were employed to
rapidly re-grid the data to different spatial resolutions for direct
comparison with the different products within TIGGE.

Using these data, a climatology of atmospheric rivers striking either
the northern or southern portions of the West coast of the US was
completed, characterizing the strength, frequency, and precipitation
impact of these events. While the IWV characteristics of atmospheric
rivers were observed more frequently during the summer, the
terrain-normal vapor flux was much stronger during the winter events.
The winter atmospheric river events were found to produce roughly twice
as much precipitation as all other storms. A publication describing this
work has been submitted to the Journal of Hydrometeorology.

To extend this climatology to the entire Pacific basin and enable
characterization of additional properties such as source region,
lifetime, and propagation speed, development of an automated atmospheric
river identification technique was begun based on the manual methods
employed for the landfalling river climatology. This technique will be
employed on both the observed fields and model products to facilitate
comparisons among the representations of the atmospheric rivers. Full
implementation will be completed in FY2008.

Finally, based on these tools, an evaluation of the representation of
the IWV fields within the TIGGE members was initiated. Pattern
correlations between the observations and analysis IWV fields as well as
comparisons of the scale and frequency of the river events are being
completed and will be presented at the 2008 AMS Annual Meeting.