Plains Elevated Convection At Night (PECAN)
Description:
The Plains Elevated Convection At Night (PECAN) special collection contains articles related to the PECAN field campaign, conducted over the Great Plains during June-July 2015. This campaign assembled a rich array of observations from lower-tropospheric profiling systems, mobile radars and mesonets, and aircraft, in order to better understand nocturnal mesoscale convective systems (MCSs) and their relationship with the stable boundary layer, the low-level jet (LLJ), and atmospheric bores. More specifically, PECAN aimed to study (a) pristine nocturnal convection initiation and the initial upscale growth of deep convection; (b) the mechanisms in which the mesoscale environment modulates the initiation, structure, propagation, and evolution of bores, solitons, and other trapped wave disturbances, and the inherent role of these disturbances in the maintenance of nocturnal MCSs; (c) the structure and evolution of the nocturnal LLJ; (d) the dynamical and microphysical structure of nocturnal MCSs; and (e) the prediction of nocturnal CI, MCSs, and, more generally, the diurnal cycle of warm season precipitation. Papers in this collection cover such topics as: instruments used for the first time or in a novel way in PECAN; the microphysics and/or the dynamics of MCSs and associated severe weather aspects; the dynamics of MCS outflow boundaries, such as density currents, bores, and solitons; the initiation of nocturnal deep convection; dynamics of the Great Plains low-level jet; nocturnal boundary-processes in the presence of a LLJ; numerical simulations of any of the above-listed meteorological topics at a range of scales, with the purpose of improving understanding as well as predictability; novel data assimilation projects and observing system simulation experiments using PECAN data, especially its mesoscale network of lower-tropospheric profiling systems.
PECAN was funded primarily by NSF, with additional funding from NOAA, NASA, DOE, and the Canadian Natural Sciences and Engineering Research Council.
Collection organizers:
David Parsons, University of Oklahoma
Bart Geerts, University of Wyoming
Tammy M. Weckwerth, NCAR
Conrad L. Ziegler, NOAA National Severe Storms Lab
David D. Turner, NOAA National Severe Storms Lab
Plains Elevated Convection At Night (PECAN)
Abstract
While radiosondes have provided atmospheric scientists an accurate high-vertical-resolution profile of the troposphere for decades, they are unable to provide high-temporal-resolution observations without significant recurring expenses. Remote sensing technology, however, has the ability to monitor the evolution of the atmosphere in unprecedented detail. One particularly promising tool is the Atmospheric Emitted Radiance Interferometer (AERI), a passive ground-based infrared radiometer. Through a physical retrieval, the AERI can retrieve the vertical profile of temperature and humidity at a temporal resolution on the order of minutes. The synthesis of these two instruments may provide an improved diagnosis of the processes occurring in the atmosphere. This study provides a better understanding of the capabilities of the AERI in environments supportive of deep, moist convection. Using 3-hourly radiosonde launches and thermodynamic profiles retrieved from collocated AERIs, this study evaluates the accuracy of AERI-derived profiles over the diurnal cycle by analyzing AERI profiles in both the convective and stable boundary layers. Monte Carlo sampling is used to calculate the distribution of convection indices and compare the impact of measurement errors from each instrument platform on indices. This study indicates that the nonintegrated indices (e.g., lifted index) derived from AERI retrievals are more accurate than integrated indices (e.g., CAPE). While the AERI retrieval’s vertical resolution can inhibit precise diagnoses of capping inversions, the high-temporal-resolution nature of the AERI profiles overall helps in detecting rapid temporal changes in stability.
Abstract
While radiosondes have provided atmospheric scientists an accurate high-vertical-resolution profile of the troposphere for decades, they are unable to provide high-temporal-resolution observations without significant recurring expenses. Remote sensing technology, however, has the ability to monitor the evolution of the atmosphere in unprecedented detail. One particularly promising tool is the Atmospheric Emitted Radiance Interferometer (AERI), a passive ground-based infrared radiometer. Through a physical retrieval, the AERI can retrieve the vertical profile of temperature and humidity at a temporal resolution on the order of minutes. The synthesis of these two instruments may provide an improved diagnosis of the processes occurring in the atmosphere. This study provides a better understanding of the capabilities of the AERI in environments supportive of deep, moist convection. Using 3-hourly radiosonde launches and thermodynamic profiles retrieved from collocated AERIs, this study evaluates the accuracy of AERI-derived profiles over the diurnal cycle by analyzing AERI profiles in both the convective and stable boundary layers. Monte Carlo sampling is used to calculate the distribution of convection indices and compare the impact of measurement errors from each instrument platform on indices. This study indicates that the nonintegrated indices (e.g., lifted index) derived from AERI retrievals are more accurate than integrated indices (e.g., CAPE). While the AERI retrieval’s vertical resolution can inhibit precise diagnoses of capping inversions, the high-temporal-resolution nature of the AERI profiles overall helps in detecting rapid temporal changes in stability.
Abstract
Extensive measurements were made of the summertime Great Plains low-level jet (LLJ) in central Kansas during June and July 2015 as a component of the Plains Elevated Convection at Night (PECAN) field study. Here, the authors describe the early phase of the LLJ development on 20 June 2015. Half-hourly soundings were launched to monitor the progress of the jet. An airborne mission was also conducted using the University of Wyoming King Air research aircraft. Vertical sawtooth patterns were flown along a fixed track at 38.7°N between longitudes 98.9° and 100.3°W to document changes in the potential temperature and wind profiles. Ageostrophic winds during the LLJ formation were also assessed. In addition, a high-resolution numerical simulation of the 20 June 2015 LLJ case was conducted using the Weather Research and Forecasting Model. Observations and model results show that the early stage of development consisted of a rapid increase in wind speed in the hours just after sunset with less pronounced directional change. The LLJ evolution is similar to that expected from an inertial oscillation of the ageostrophic wind following the stabilization of the near-surface layer.
Abstract
Extensive measurements were made of the summertime Great Plains low-level jet (LLJ) in central Kansas during June and July 2015 as a component of the Plains Elevated Convection at Night (PECAN) field study. Here, the authors describe the early phase of the LLJ development on 20 June 2015. Half-hourly soundings were launched to monitor the progress of the jet. An airborne mission was also conducted using the University of Wyoming King Air research aircraft. Vertical sawtooth patterns were flown along a fixed track at 38.7°N between longitudes 98.9° and 100.3°W to document changes in the potential temperature and wind profiles. Ageostrophic winds during the LLJ formation were also assessed. In addition, a high-resolution numerical simulation of the 20 June 2015 LLJ case was conducted using the Weather Research and Forecasting Model. Observations and model results show that the early stage of development consisted of a rapid increase in wind speed in the hours just after sunset with less pronounced directional change. The LLJ evolution is similar to that expected from an inertial oscillation of the ageostrophic wind following the stabilization of the near-surface layer.
