Fine-scale Structure of the 2-3 February 2015 Nor'easter using high-resolution HIAPER Cloud Radar Observations

On 2 February 2015, the HIAPER Cloud Radar (HCR) aboard the National Center for Atmospheric Research Gulfstream-V High-Performance Instrument Airborne Platform for Environmental Research (HIAPER) aircraft flew over a Nor’easter cyclone along six flight legs, all between the northern tip of Delaware Bay and Bangor, Maine, to observe the fine-scale structure of the storm. The HCR is a W-band, dual-polarization, Doppler research radar which records reflectivity, radial velocity, spectral width, and linear depolarization ratio with a 0.7º beam pointed at nadir. The range resolution used this day was 19.2 m with the along track resolution between 20 and 200 m, depending on radial distance.

The air mass structure, vertical motions, boundary layer structure, cloud-top generating cells, layers of turbulence and other fine-scale features, characterized using cross-sections of the detailed HCR observations of reflectivity, radial velocity, spectral width and linear depolarization ratio, were often on a scale of 5 km or less, and varied significantly with horizontal distance. The air mass origin and structure associated with features was determined using back trajectories from the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model. By overlaying thermodynamic fields from the Weather Research and Forecasting (WRF) model on the radar cross sections, the air mass structure, layers of stability/instability, and frontal boundaries were related to the generating cells, elevated convection, gravity waves, boundary layers circulations, and other features observed by the HCR within the Nor’easter. The sources for these radar-determined features will be discussed.