Wallops Island, VA

Project

High-resolution analyses/ forecasts of refractivity and EM propagation conditions for use in Naval operations have been archived for the 1.5-month period of the Wallops-2000 experiment and saved on the Master Environmental Library (MEL).  This unique model and observational database is now available for wide usage in the EM propagation and modeling research communities and is available at http://mes.dmso.mil.  Individual case studies were analyzed using the forecasts and observational data and error statistics have been compiled to assess COAMPS capability in forecasting modified refractivity and the evolution of 3-dimensional ducting layers.

Results

Figure 1 shows the full 1.5 month-long time series at the NPS Buoy located ~12 km offshore of Wallops Island, VA.  COAMPS forecasts of wind direction and speed, temperature and relative humidity are in blue and buoy observations are in red.  Statistics for this period indicate good agreement between model-obs with RMS errors of 2.2 m s^-1 for wind speed, 1.3°C for temperature and 7.7% for relative humidity. 

Results from individual case study analysis are shown in Fig. 2 and 3.  Figure 2a depicts near-surface streamlines, surface temperature, and white, cloud-like isosurfaces of trapping [ dM/dz < 0] at 3 am LT on 29 April 2000.  The land (blue) is significantly colder than the SST at this hour. The wind is northerly over most of the region, although a low-pressure center lies near the grid’s eastern boundary.  On the backside of the low, dry subsiding air creates patchy, elevated trapping regions throughout the night.  With daytime heating, the situation changes dramatically.  By 3pm LT (Fig. 2b), the land is substantially warmer than the coastal waters, and the flow has shifted to the NW.  Shallow, near-surface trapping layers develop in the stable internal boundary layers ’s formed over coastal waters where the afternoon flow is offshore.  The flow along the New Jersey coast is onshore in Fig. 2b and no trapping is present.  A 24h long trajectory descends from 1.3 km at point 1 to a height of 5 m near Wallops being drawn onshore by the sea breeze.  Dry air is advected along such parcel trajectories, altering the near surface refractivity profile, and making simple 2D sea/land breeze concepts of limited value in this region. 

Figure 3 shows the dramatic evolution of the marine layer over a 2-hour period during 7 April 2000.  In Fig. 3a, the subsiding return flow within the afternoon sea-breeze circulation suppresses and tightens the inversion to strengthen ducting while the warm, moist air over the Gulf stream provides a less favorable environment for trapping EM energy.  Two hours later, trapping is confined to near the coastline as a warm front ushers in a deep moist layer from the south eliminating the moisture inversion and much of the low-level ducting.