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What is PECAN?

The PECAN (Plains Elevated Convection at Night) 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 over the Southern Great Plains with a stable boundary layer (SBL), a nocturnal low-level jet (NLLJ) and the largest CAPE (Convectively Available Potential Energy) located above the SBL. Thunderstorms are most common after sunset across this region in summer and much of the resulting precipitation falls from mesoscale convective systems (MCSs). Nocturnal MCSs may produce heavy rainfall; their intensity is correlated with the NLLJ. To date, an accurate prediction and an in-depth understanding of elevated convection in this environment remains an elusive goal.

The basic questions motivating the PECAN project are simple to ask, but hard to answer:

- It has long been known that in summer, thunderstorms and convective precipitation are most frequent not in the afternoon, but rather after sunset, in a large swath of the Great Plains. What explains this nocturnal peak?

- How do the dynamics and microphysics of MCSs evolve as the boundary layer stabilizes in response to nocturnal radiative cooling?

- How can scientists better predict these convective systems and the heavy rainfall they produce and enhance their understanding of said continental, nocturnal, warm season precipitation?

PECAN is the first large coordinated effort to study the interrelationship between (1) the initiation of elevated deep convection, (2) the dynamics and microphysics of nocturnal MCSs, and (3) the properties of high-amplitude SBL disturbances. These results are relevant to the goal of improving numerical weather prediction systems. PECAN’s focus on elevated nocturnal convection and on stable layer disturbances distinguishes it from other campaigns that have studied deep convection in the central USA.

PECAN will be conducted in the central Great Plains between 1 June and 15 July 2015. The spatio-temporal domain is chosen based on the climatologies of deep convection, MCSs, NLLJs, and bores, as well as on field deployment considerations and existing facilities, such as the ARM Southern Great Plains site and WSR-88D radars. The PECAN campaign will utilize three aircraft: the NSF University of Wyoming King Air and the NASA DC-8 will probe the pre-convective environment, and the NOAA P-3 will study the microphysical characteristics of developing and mature stratiform regions of MCSs. PECAN will deploy scanning Doppler radars and lidars, radiosonde systems and experimental profiling sensors such as DIfferential Absorption Lidars (DIAL) & Raman lidars, multi-channel microwave radiometers, infrared spectrometers, and acoustic systems. A unique aspect of the experimental design is the incorporation of these profiling systems into the PECAN Integrated Sounding Array (PISA). Each of the 10 PISA units will be highly complementary in their capability to profile wind, thermodynamics, water vapor, and aerosols.

In addition to this broader impact, PECAN research will also impact the nation’s NWP capabilities through collaborative efforts between the academic community and NOAA’s National Severe Storms Laboratory (NSSL) aimed at assessing the increasing dependence of storm-scale prediction on numerical modeling, as in the Warn-on-Forecast Initiative. NSSL is planning to commit mobile radars and sounding units, with final approval pending NSF’s commitment to PECAN. The broader impact of PECAN is further driven by the importance of nocturnal precipitation to the hydrology and agriculture of the region, the public safety risk of MCS-related severe weather, and the applicability to other regions with nocturnal thunderstorm maxima in LLJ environments (e.g., Johnson 2011) and to climate models, which poorly capture the diurnal cycle of precipitation over this region (Pritchard et al. 2011). Finally, numerous students will participate in the data collection and visit the instruments operating in the field campaign.

The PECAN domain encompasses central and western Kansas, as well as adjacent parts of mainly Nebraska and Oklahoma. Its location is driven by climatological information. Its size is determined by the maximum driving distance from Hays, KS, about 350 km, for mobile units in anticipation of an IOP.

PECAN scientists will hit the road in late May, and the project will run from 1 June through 15 July 2015.

PECAN Domain

More about PECAN . . .

35 science vehicles and platforms
.
Steering Committee
Principal Investigators
       80 Scientists / Crew
.

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Field Phases:

1 June - 15 July 2015

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