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

Proposed Work Plan for NOAA/ESRL/PSD2

FY 2008

Gary Wick

**Objectives**

The overall focus of this work will be to assess the diagnostic utility
of satellite-derived integrated water vapor (IWV) and wind vector
products for independent validation of forecast models and
characterization of high-impact weather events in the western US.
Specific objectives include:

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

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

**Research Activities**

The satellite IWV and vector wind retrievals will be utilized to
evaluate multiple models being developed or applied within THORPEX. The
first component of this work will be to validate and compare the ability
of analyses and forecasts from multiple models within the THORPEX
Interactive Grand Global Ensemble (TIGGE) and North American Ensemble
Forecast System (NAEFS) to reproduce the occurrence of and distribution
of water vapor within atmospheric river events in the Pacific basin.
Control and ensemble mean forecasts at multiple lead times from the
ECMWF, NCEP, CMC, UK Met Office, and JMA models within TIGGE are being
saved on site along with the corresponding IWV retrievals. Regular
archival of the NAEFS products will be added. The satellite data will be
processed to multiple resolutions corresponding to those of the model
products to enable fair and direct comparisons. Specific questions to be
addressed include: Do the forecasts accurately predict the frequency of
occurrence of the atmospheric river events? Does the predicted frequency
change with the forecast lead time so that the events tend to be under-
or over-predicted as the forecast lead increases? Is the width of the
rivers reproduced well or are features overly smooth? Do the models
accurately forecast tapping of tropical moisture when this is observed?
Is there any model that performs significantly better? Special emphasis
will be placed on the NAEFS forecasts to evaluate what improvements are
brought about with the joint ensemble forecasts. To facilitate answering
these questions, work begun in the first year to objectively identify
and characterize atmospheric river events in both the observation and
forecast fields will be completed. The analysis is planned to encompass
several seasons of data beginning with Spring 2007. Through interaction
with project leaders at NCEP, the knowledge gained can be applied to
improvements in the NCEP Global Forecast System (GFS) forecasts.

As an addition to the project, the evaluations of the models within
TIGGE and NAEFS will be extended to include the new Flow-following
finite-volume Icosahedral Model (FIM) recently developed at the Global
Systems Division of NOAA/ESRL. The new model incorporates constant
potential temperature vertical coordinate surfaces enabling the model to
be flow-following as well as an icosahedral horizontal grid that allows
conservative finite-volume numerics. These additions are expected to
result in improvements to the accuracy of the resulting global numerical
predictions. The satellite IWV observations of atmospheric rivers will
be used to evaluate the representation of water vapor and atmospheric
river events in the new FIM and compare the results with those obtained
with the GFS and other models. Real time forecasts began after February
2008. Real-time access to the water vapor forecasts will be initiated
and the questions listed in the paragraph above will all be
investigated. The focus will be on determining if any improvement in the
reproduction and representation of atmospheric river events is achieved
with the new model. Since the available data begins near the end of the
normal atmospheric river season this year, comparisons in this project
year will be preliminary in nature.

The second component of model evaluation will consider the ensemble
forecasts generated within PSD by Dr. Jian-Wen Bao. New ensemble
simulations are being performed by Dr. Bao utilizing different physical
formulations and detailed validation is required to assess the accuracy
of the formulations. The observed wind vector and IWV products will be
used to determine whether the ensembles have captured the full spread of
possible conditions. This analysis will focus on the experimental
periods selected by Dr. Bao.

The satellite data evaluations will further contribute to more general
efforts within the THORPEX to explore the optimal use of satellite data.
Collaborative work will explore the utility of the data to assist in
targeted observations both as part of the Winter Storms Reconnaissance
(WSR) program and THORPEX Pacific-Asian Regional Campaign (T-PARC).
Within WSR, regions where forecasts are most sensitive to the conditions
are identified and targeted for additional observations. Our work will
explore the relationship between the identified sensitive regions and
any specific features such as atmospheric rivers. The objectives include
determining whether there are certain features that appear regularly in
the vicinity of the sensitive regions, what about the features leads to
the increased sensitivity (e.g., poor representation in the models
and/or data), are the features accurately represented in the model
fields, and how can the feature observations best be merged with the
model-identified sensitivities for optimal targeting. Initial test cases
will include joint flight planning between this year's WSR program and
forecast efforts within the Hydrometeorology Testbed (HMT) and
historical cases where flights jointly targeted key features and
sensitive regions. We will further develop and provide characteristics
of the satellite data sets including error statistics for use in
observation system design research. This work will be performed in
cooperation with Yucheng Song and other NOAA THORPEX investigators.

Observational analyses producing a climatology of atmospheric river
events in the Pacific Ocean will continue. Previous work has produced
the required IWV products and a climatology of landfalling events. The
climatology will document parameters such as river strength, formation
region, propagation speed, and whether there is any direct connection to
tropical moisture. A key aspect will be to determine if there is any
relationship between river event frequency and the state of ENSO and the
Madden-Julian oscillation (MJO). The results will be applied to efforts
to improve intraseasonal forecasting and address the linkage between
weather and climate scale forecasts. Efforts will evaluate if knowledge
of the ENSO and MJO states can be used to assess changes in the
probability of atmospheric rivers and major winter precipitation events
in the western US on scales between 14 and 60 days. On shorter time
scales the results will be used along with those of the landfalling
event climatology to evaluate the utility of knowledge of the position
and strength of atmospheric rivers for improving the prediction of the
specific location and timing of the significant precipitation events.

The IWV retrievals are obtained from the Special Sensor Microwave/Imager
(SSM/I) and are available for all applications following the work of
year 1. The wind vector retrievals will be derived from the QuikSCAT
scatterometer. While 0.25 degree resolution retrievals are currently
archived at NOAA ESRL, real-time access to higher resolution 12.5 km
data from NOAA NESDIS must still be implemented.

**Year 2 Milestones**

-   Implement real-time access to high resolution QuikSCAT data at NOAA
    ESRL.

-   Completion of objective atmospheric river identification and
    characterization technique.

-   Complete assessment of TIGGE and NAEFS forecasts of atmospheric
    rivers and communicate scientific findings.

-   Collaborate with Dr. Jian-Wen Bao on the assessment of his new
    ensemble simulations.

-   Begin assessment of linkages between specific features and
    identified sensitive regions in targeted observations.

-   Complete atmospheric river climatology over Pacific basin and assess
    linkage of river strength and frequency to ENSO and MJO.

-   Collaborate on evaluation of data utility for adaptive observations.

-   Initiate real-time access to and archival of the FIM forecasts of
    integrated water vapor.

-   Begin assessment of the representation of atmospheric rivers and the
    distribution of water vapor within the FIM forecasts and compare
    with the forecasts from TIGGE and NAEFS.