Ian Morrison, Steven Businger, and Annette Baerman, University of Hawaii,
Roland Draxler, NOAA/ARL, Robert Tuleya, NOAA/GFDL
In preparation for field deployment of NOAA/UH Smart Balloons into a hurricane inflow layer, output from past Geophysical Fluid Dynamics Laboratory (GFDL) Hurricane Prediction System model runs are utilized to identify strategic launch sites and times that provide the most favorable trajectories to satisfy the observational objectives. The Hybrid Single-Particle Lagrangian Integrated Trajectories (HY-SPLIT) model uses 6-hourly winds from the GFDL model to construct constant density air-parcel trajectories (Draxler 1992). GFDL model output is also used to investigate changes in the energetics of inflow air in the model hurricane, as a prelude to comparisons with in situ observations from balloon, dropwinsonde, and research aircraft from the upcoming field experiments. Results from the model trajectory analyses are presented with a discussion of their implications for field experiment strategy. During the field experiments the release points will be determined by a team of scientists and forecasters with the aid of a range of model and operational data at NHC/HRD.
Sample 24-hour trajectories at 500 and 700 m were calculated applying the HYSPLIT model to output from the GFDL hurricane model from Hurricane Opal (1995) and Floyd (1999) (Fig. 1a , 1b and 1c ). Trajectories are deemed successful if they enter the eyewall (Fig. 2a , 2b and 2c ). Trajectories released to the rear of the propagating hurricane had the highest success rate. This trajectory takes the straightest path to the eyewall, traveling through the right-rear quadrant of the hurricane, and enters the core most quickly. The trajectories released left of the propagating hurricane also had a high incidence of success traveling around the rear quadrants and entering the eyewall in either of the front quadrants. Release points to the right tended to propagate well ahead of the hurricane and had the least amount of success.
The trajectories that reached the eyewall have similar general properties. As the path approaches the center of the hurricane the equivalent potential temperature (q) increases and the trajectory speed increases until the trajectory reaches the inner core (Fig. 3a , 3b and 3c ). The maximum q and speeds are obtained at this point. Once the air parcel reaches the inner core of the hurricane it is advected cyclonically by the inner core winds; and the distance from storm center, trajectory speed, and q tend to oscillate.
Draxler, R.R., 1992: Hybrid single-particle Lagrangian integrated trajectories (HY-SPLIT): Version 3.0 - Users guide and model description. NOAA Tech. Memo. ERL ARL-195.