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Rainfall Forecast Validation Team
Team Leaders:
Robert Rogers (NOAA/HRD)
Tim Marchok (NOAA/GFDL)
Robert Tuleya (NOAA/NCEP/EMC/SAIC)
Manuel Lonfat (RSMAS)
Team Objective:
One of the most significant impacts of tropical cyclones is the copious amount
of rainfall they often produce. Drowning from inland flooding in landfalling
tropical cyclones is the leading cause of death from storms affecting the
United States in the past 30 years. For this reason, the Tropical Prediction
Center has stated that one of its highest priorities is to improve quantitative
precipitation forecasting (QPF) for tropical cyclones. Dynamical numerical
models provide one way of forecasting rainfall from tropical cyclones. While
such models enable the depiction of the temporal and spatial evolution of
tropical cyclones and their associated rain fields, they often exhibit errors
related to inadequate initial conditions and model physics. Knowledge of these
errors can aid the forecaster in interpreting numerical guidance of rainfall
and adjusting their forecasts accordingly.
An accurate diagnosis of rainfall forecast errors requires a validation scheme
that accurately measures the performance of the forecast system. However, no
standard technique has been developed to validate rainfall forecasts from
tropical cyclones. Most rainfall forecasts involving landfalling TC's have
been validated on fixed domains using standard validation metrics, such as
bias and equitable threat score, that do not specifically account for the
presence of the TC. As a result, many important features of the rainfall
field that are related to the TC are overlooked. A QPF validation technique
specific to TCs is therefore needed to better identify biases in the forecasts
and lead to possible improvements in them.
Work in this team will be directed toward developing new techniques that
address these issues. The validation schemes will be implemented using
forecasts of landfalling tropical cyclones from the operational GFDL, GFS, and
Eta models and the benchmark Rainfall CLIPER product against observed rain
fields provided by the National Precipitation Validation Unit (NPVU) dataset.
Another aspect of this work that is advancing is the quantification of the
impact of vertical shear on the distribution of rainfall and its incorporation
into a parametric model, the benchmark rainfall climatology and persistence
model (R-CLIPER).
Accomplishments:
- Devised a technique for validating tropical cyclone rainfall by comparing
the performance of the GFDL, GFS, and Eta models in several different rainfall
attributes important in TC rainfall: pattern reproduction, mean and volume,
extreme rainfall amounts, and sensitivity to track error;
- Completed validation of these models on all U.S. landfalling tropical
cyclones from 1998 to 2004;
- Completed quantification of the impact of vertical shear on the
distribution of rainfall;
- Incorporated this impact into a modified R-CLIPER parametric rainfall
model.
Milestones:
- Compare modified version of R-CLIPER with the other models using the same
validation techniques described above;
- Compile statistics summarizing performance of all models (GFDL, GFS, Eta,
R-CLIPER, shear-modified R-CLIPER) based on the four parameters mentioned above
- Finish manuscript summarizing these comparisons, submit to Weather and
Forecasting.
- Finish manuscript describing parameterization of shear impacts on rainfall
fields, submit to Monthly Weather Review;
- Consider other elements quantify and include in parametric model (e.g.,
topography).
References:
- Black, M.L., J.F. Gamache, F.D. Marks, C.E. Samsury, and
H.E. Willoughby, 2002: Eastern Pacific Hurricanes Jimena of 1991 and
Olivia of 1994: The effect of vertical shear on structure and
intensity. Mon. Wea. Rev., 130, 2291-2312.
- Corbosiero, K.L., and J. Molinari, 2002: The effects of vertical
wind shear on the distribution of convection in tropical cyclones.
Mon. Wea. Rev., 130, 2110-2123.
- Lonfat, M., F.D. Marks, Jr., and S.S. Chen, 2004: Precipitation
distribution in tropical cyclones using the Tropical Rainfall Measuring
Mission (TRMM) Microwave Imager: A global perspective. Mon. Wea.
Rev., 132, 1645-1660.
- Lonfat, M., S.S. Chen, J.A. Knaff, and F.D. Marks, Jr., 2005:
Effects of environmental vertical wind shear and storm motion on
tropical cyclone rainfall asymmetries deduced from TRMM. Submitted
to J. Atmos. Sci.
- Rogers, R.F., S.S. Chen, J.E. Tenerelli, and H.E. Willoughby,2003:
A numerical study of the impact of vertical shear on the distribution
of rainfall in Hurricane Bonnie (1998). Mon. Wea. Rev., 131,
1577-1599.
- Tuleya, R.E., M. DeMaria, and R. Kuligowski, 2005: Evaluation of
GFDL model rainfall forecasts for U.S. landfalling tropical storms.
Manuscript to be submitted to Wea. And Forecasting.
- Tustison, B. D. Harris, and E. Foufoula-Georgiou, 2001: Scale
issues in verification of precipitation forecasts. J. Geophys. Res.,
106, 11,775-11,784.
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Last modified: 5/16/2005
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