High temporal resolution proximity observations of atmospheric stability during instances of nocturnal convective initiation

The role of insolation and other triggers in the development of daytime convection has been extensively studied, but comparatively little attention has been paid to the initiation of nocturnal convection, resulting in degraded forecast skill at night. One of the scientific aims of the Plains Elevated Convection At Night (PECAN) field experiment is to investigate the environments in which nocturnal convective initiation (CI) occurs in order to better understand the processes at work. To that end, a fleet of instrument vehicles was deployed across the central United States in order to have in situ and remote observations adjacent to nocturnal convective phenomena.

Two similar mobile profiling units were often deployed in tandem during PECAN. These units, the University of Wisconsin-Madison's Space Science and Engineering Center (SSEC) Portable Atmospheric Research Center (SPARC) and the University of Oklahoma's Collaborative Lower Atmosphere Mobile Profiling System (CLAMPS) both contain an Atmospheric Emitted Radiance Interferometer (AERI) and a Doppler lidar wind profiler in addition to surface meteorology instrumentation. Radiance observations from AERI can be used to retrieve profiles of atmospheric temperature and moisture at a temporal resolution of up to 30 s. Time series of indices of atmospheric stability can be calculated from the retrieved thermodynamic profiles.

As both SPARC and CLAMPS were frequently deployed in regions where nocturnal CI was occurring, the evolution of the stability of the atmosphere in close proximity to these events can be seen in detail far greater than possible with ordinary soundings from the existing upper-air radiosonde network. Trends in stability both before and after initiation will be presented for both individual cases as well as in aggregate. Collectively, these observations show small-scale variability in instability both spatially and temporally, indicating the need for enhanced boundary layer observations in order to better understand and predict these phenomena. Data from collocated research radiosonde launches will also be shown to validate and augment the remotely-sensed observations.