Observations of a Cold Front at High Spatiotemporal Resolution Using an X-Band Phased Array Imaging Radar

While the vertical structure of cold fronts has been studied using a variety of methods, previous research has shown that traditional methods of observing meteorological phenomena (such as pencil-beam radars) are not well-suited for resolving small-scale cold front phenomena. One reason for this is low spatial and temporal resolution, as the evolution of small-scale phenomena is not well-captured. Additionally, non-simultaneous elevations within a given vertical cross-section can lead to errors in analysis, as differential vertical advection cannot be distinguished from temporal evolution while the radar is in plan position indicator (PPI) mode, or to a lesser extent in range-height indicator (RHI) mode. In this study, a cold front from 19 September 2015 is analyzed using the Atmospheric Imaging Radar (AIR). The AIR transmits a 20-degree fan beam in elevation, and digital beamforming is used on receive to generate simultaneous receive beams. This mobile, X-band, phased-array radar offers temporal resolution on the order of 1 s while in RHI mode, range resolution of 37.5 m (typically oversampled to 30 m), and continuous data in the vertical dimension, which can be arbitrarily oversampled (typically to 0.5 degrees in elevation). The ability of the AIR to obtain simultaneous RHIs at high temporal resolution without any mechanical steering allows for unique analysis of the vertical structure of a cold front that would otherwise not be possible. Features such as Kelvin-Helmholtz instabilities, low-level mass transport (feeder flow), longitudinal and transverse jet oscillations, and regions of heightened spectrum width will be shown and discussed.