Validation of Planetary Boundary Layer Parameterizations over the Coastal Ocean of Southern New England Using the IMPOWR Field Campaign

Winds, temperatures and moisture in the planetary boundary layer (PBL) are often difficult for operational models to predict given the relatively sparse observations and that most model PBL parameterizations were developed over inland locations. Coastal marine layer forecasts are important for the forecasting of severe storms and wind energy resources in the highly populated coastal marine environment of the Northeast U.S. (NEUS). Mesoscale models are known to have large biases in wind speeds and temperatures at these lower levels over coastal waters. The goal of this project is to evaluate the performance of six PBL schemes in the Weather Research and Forecasting (WRF-ARW) model version 3.4.1 in the coastal marine environment of the NEUS. This study region, stretching from the south shore of Long Island out to Georges Bank, is home to not only major shipping lanes and the commercial fishing industry, but is also an ideal location for an offshore wind energy grid based on such factors as regional energy demand, water depth, and available wind resource.

This talk will focus on the IMPOWR (Improving the Mapping and Prediction of Offshore Wind Resources) field study, which is a marine observational campaign of the PBL consisting of high-frequency Long-EZ aircraft measurements and instrumented offshore towers. During the spring and summer of 2013 several high-frequency instruments were installed on the Air-Sea Interaction Tower (ASIT) south of Martha's Vineyard and the Cape Wind tower located in Nantucket Sound. The instrumentation consisted of sonic anemometers, temperature and relative humidity sensors, and an optical wave gauge. A Long-EZ aircraft capable of taking high-frequency temperature, relative humidity, and three-dimensional wind measurements performed 10 flights in the study region from April to June 2013. The aircraft observations combined with the tower observations allowed us to construct full vertical profiles of wind speed, temperature, and humidity from the surface to the top of the marine boundary layer.

Verification of the six WRF PBL schemes (two non-local, first-order schemes and four local, TKE-order schemes) was primarily done using a dataset of observations at multiple levels from the Cape Wind tower in Nantucket Sound from 2003 to 2011, as well as dozens of surrounding NDBC and ASOS stations. A series of 30-hour WRF runs were conducted for 90 randomly selected days between 2003 and 2011, with initial and boundary conditions supplied by the North American Regional Reanalysis (NARR). Additional model verification will be presented from the Long-EZ flights during the field campaign. Preliminary results from flights on 12 November 2012 and 16 May 2013 showed that the models consistently underestimated wind speeds and relative humidity in the marine boundary layer, while overestimating temperatures. Future analysis will include looks at how the PBL schemes handle specific sea-breeze and coastal jet cases, as well as further verification using aircraft-observed TKE values over ocean and coastal environments.