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Extratropical Transition
The third T-PARC component is aimed at identifying important physical characteristics associated with the extratropical transition
(ET) of tropical cyclones. In the United States, this portion of T-PARC is primarily funded by the National Science Foundation with
funding also from the Office of Naval Research for shared aircraft resources. Also, major contributions to the ET and downstream impacts
components of T-PARC come from DLR for funding the Falcon aircraft and FZK in Germany.
Numerical forecast skill over near-hemispheric scales is often reduced during periods of ET.
In addition, uncertainty in the evolution of the midlatitude flow downstream is often increased following an ET event. In the diagram below,
standard deviation of 500 hPa heights among ensemble members from the National Centers for Environment Prediction (NCEP) Global Forecast System
(GFS) ensemble prediction system (EPS) is increased downstream of the ET of Typhoon Nabi.
The increased uncertainty downstream of an ET event is often related to the forcing of a Rossby wave-like pattern that may occur downstream.
As indicated in the pattern of 500 hPa height anomalies in the chart below, this was clearly important downstream of Typhoon Nabi. However, this
response does not always occur as is evident in the pattern of 500 hPa height anomalies downstream of Typhoon Saola.
The objective is to understand the relative role(s) of the complex physical processes that occur during ET in contributing to reduction
of forecast skill. The primary observation platforms are the WC-130J from the 53rd Weather Reconnaissance Squadron at Keesler Air Force Base,
the Navy Research Laboratory P-3B, and the DLR Falcon. Each aircraft is equipped with special instrumentation to obtain in situ measurements of
thermodynamic and dynamic properties at flight level, throughout vertical profiles, and at the surface. The NRL P-3 will contain the ELDORA
Doppler Radar to obtain high-resolution structures associated with the evolution of deep convection during formation and intensification.
The DLR Falcon is equipped with a Doppler wind lidar and Differntial Absorption water vapor lidar. All aircraft have dropwindsonde capability.
Aircraft operations will be defined to make optimum use of the special capabilities of each aircraft.
The primary objectives associated with the ET and downstream impacts portion of T-PARC are defined with respect to:
- Physical Mechanisms during ET
- Sensitivities due to TC/ET characteristics
- Influence of TC structure
- Outflow
- Warm frontogenesis and its impact on the midlatitude flow
- Sensitivities due to midlatitude flow characteristics
- Understanding the impacts on predictability
- Ensemble spread
- Forecast error growth
- Timing/extent/persistence of the downstream response
- Sensitivities to initial conditions and their propagation throughout the forecast cycle
- Increasing Predictability
- Predict the reduction in forecast error variance due to supplemental/targeted observations
- Test new strategies and observational systems
- Data assimilation strategies, impacts.
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