The PECAN campaign is envisioned as a multi-agency project (NSF, NOAA, NASA, DOE) designed to advance the understanding of continental nocturnal warm-season precipitation. PECAN will focus on nocturnal convection in conditions with a low-level jet and a stable boundary layer with the largest Convectively Available Potential Energy located aloft. The findings should be applicable to other continental regions with nocturnal thunderstorm maxima. PECAN has four research foci: i) Nocturnal convective initiation; ii) Bore disturbances; iii) Nocturnal mesoscale convective systems (MCSs); iv) Prediction of nocturnal convection. PECAN will be conducted across northern Oklahoma, central Kansas and into south-central Nebraska from 1 June to 15 July 2015. The PECAN campaign calls for three aircraft with the NSF-University of Wyoming King Air and the NASA DC-8 probing the pre-convective environment and the NOAA P-3 observing the dynamical and microphysical characteristics of MCSs. The project design includes the NCAR S-POL radar and several mobile and fixed scanning Doppler radars. A unique aspect of the experimental design is the integration of a wide variety of profiling systems into a fixed and mobile PECAN Integrated Sounding Array (PISA) including Differential Absorption Lidars, Doppler lidars, and Raman lidars, multi-channel microwave radiometers, infrared spectrometers, and acoustic systems. Each of the 10 proposed PISA units will be highly complementary in their capability to profile wind, temperature, water vapor, and aerosols. PECAN proposes supplemental radiosonde soundings from National Weather Service and DOE sites associated with their Southern Great Plains measurement facility.
Intellectual Merit : It is well established convection is most common after sunset across the Great Plains in summer, and much of the resulting precipitation falls from MCSs. Considerable scientific debate, however, exists in the literature as to the dynamical mechanisms that initiate, organize and maintain this nocturnal convection. Recent modeling and observational case studies have shown that nocturnal convection in this stable, low-level jet environment frequently triggers bores, undular bores and solitary waves [hereafter referred to as bores]. These bores are associated with intense upward net parcel displacements (e.g., 0.5-1.0 km) in the lowest ~3 km, which destabilizes the nocturnal environment. While idealized modeling studies suggest that bore lifting can maintain convection in the presence of a nocturnal stable layer, little observational evidence exists for any feedbacks between this lifting and the organization, intensity, initiation and maintenance of nocturnal systems. PECAN will be the first modern campaign designed to examine bore structure and these potential feedbacks, which distinguishes it from other campaigns that have studied deep convection in the central USA. Since the generation and structure of these disturbances depends on the details of the MCS cold pool and storm-relative flow patterns, PECAN will address the dynamics and microphysics of nocturnal MCSs as well as the initiation and prediction of nocturnal convection.
Broader Impacts : The PISA measurement approach makes PECAN particularly well suited to testing the national goals outlined in "Observing Weather and Climate from the Ground Up: A Nationwide Network of Networks" (NRC 2009), "When Weather Matters: Science and Service to Meet Critical Societal Needs" (NRC 2010) and the follow-up workshop on in the US, Thermodynamic Profiling Technologies (Carbone et al. 2012) and Canada. The project has considerable educational involvement through graduate students and potential links to REU programs. The broader impact of PECAN is also driven in large part by poor prediction of nocturnal convection coupled with their importance to hydrology, energy and agriculture and the public safety risk of MCS severe and hazardous weather. PECAN research will impact the nation's forecasting and numerical weather prediction capabilities through collaborative efforts between the academic community and NOAA's National Severe Storms Laboratory. The effort is highly relevant to NOAA's goal to assess the increasing dependence of storm-scale prediction on numerical modeling, as in the Warn on Forecast Initiative. The project will assist in developing and applying space-based remote sensing, weather prediction and climate modeling through NASA participation.
The National Science Foundation award was associated with the approval of the Scientific Program Overview (SPO) proposal for the PECAN (Plains Elevated Convection at Night) field campaign. The funding of this award and the approval of the SPO is part of the competition process that National Science Foundation utilizes in the selection of large field campaigns in the Geosciences. PECAN is associated with the need to better understand and predict nocturnal (night-time) storms over the Great Plains of North America. The presence of night-time systems over the Great Plains stands in contrast to the behavoir of storms over most other land-based locations as solar heating tends to increases the temperatures in the atmospheric boundary layer during day, which increases the liklihood of storm development during day-time and early evening hours. In contrast, the lower atmosphere becomes cooler and more stable at night, and hence, less favorable for storm development. While the preference for night-time storms over the Great Plains has been known for decades, considerable debate still exists as to why night-time storms occur over the Great Plains as conditions are less favorable. The scientific merit of PECAN is that the effort will attempt to improve our understanding of why these night-time storms are prevalent over the Great Plains during the warm season with the goal of advancing the prediction and forecasting of these events. The studies under PECAN range from observational efforts to numerical modeling and advanced data assimilation techniques to improve the initial conditions for modeling efforts. Prior to PECAN, the observations were not available to answer this question. PECAN wil focus on five areas: 1) The initiation of elevated, nocturnal convection 2) The dynamics, internal structure and microphysics of nocturnal convective systems 3) Disturbances such as bores that exist in the stable nocturnal environment and may initiate or help maintain night-time storms 4) Improved prediction and night-time storms The program has numerous broader impacts. For example, in addition to this scientific debate and of more practical importance to the public is that night-time storms over the Great Plains are relatively poorly predicted by those numerical weather prediction models utilized by forecasters to warn the public of precipitation events hours or even days in advance. The public safety implications are significant as the majority of flash flood events in the eastern 2/3rds of the United States occur at night. Night-time storms are also poorly represented in seasonal prediction models and in climate simulations. The need for accurate seasonal prediction over this region is driven by the fact that the area is an important agricultural region for the country in terms of wheat, corn and other corps. Another broader impact is education as over 40 undergraduate students will be in the field for the effort and numerous MS thesis and PhD dissertations will be generated from these data sets. This grant award supported the development of the experimental design for PECAN including funding travel for those scientists involved in the PECAN planning. The field campaign is a major community effort involving three instrumented research aircraft (NASA DC-8, U Wyoming King Air, NOAA P-3), an S-band scanning Dopper radars called the NCAR S-POL, multiple, mobile scanning radars at C- and X-band. mobile radiosonde systems and collection of advanced instrument facilities to profile wind, temperature and moisture in the lower atmosphere. These integrated facilities are compose the PECAN Integrated Sensing Array). The field facilities for PECAN and an example of a possible deployment are shown in Fig. 1a and 1b.
