
Mobile Soundings for the Verification of the Origins of Rotation in Tornadoes Experiment 2 (VORTEX2) Morris Weisman, George Bryan (Co-Dropsonde PIs) National Center for Atmospheric Research Matt Parker (MGAUS PI) Dept. of Marine, Earth, and Atmospheric Sciences, North Carolina State University Chris Davis, David Dowell, Chris Snyder, Jenny Sun National Center for Atmospheric Research Jeff Trapp Dept. of Earth and Atmospheric Sciences, Purdue University Lance Bosart Dept. of Earth and Atmospheric Sciences, The University at Albany/SUNY David Stensrud NOAA National Severe Storms Laboratory 14 September 2007 1 1. Summary The Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX2) is a multi-agency field program to investigate tornadic storms and their environments, and is proposed to take place in the United States Great Plains during the months of April-June, 2009-2010. The present proposal addresses the needs for mobile soundings to enhance the observational capabilities for VORTEX2, especially regarding the scientific foci addressing the relationships between supercell storms and their environments and numerical weather prediction. Mobile soundings, specifically the Mobile GPS Advanced Upper Air System (MGAUS) and the GPS Dropsonde system, will be used to enhance the observations of the pre- and during-storm mesoscale environments of tornadic storms, with emphasis on documenting both the larger scale forcing features that may be critical to storm initiation and the smaller scale environmental heterogeneities (e.g., pre- existing boundaries) that may be important for tornadogenesis. Dropsondes represent the best technology available for targeting different geographical regions from day-to day, and obtaining the required horizontal and vertical resolution of observations throughout the troposphere to meet the VORTEX2 scientific objectives. The MGAUS can provide observations in specific storm-relative locations that are required to document features such as pre-existing boundaries in the near-environment of storm updrafts, and can provide coverage where a dropsonde aircraft would be prohibited due to ongoing weather hazards. Mobile sounding information will be used along with other field observations (from mobile, ground-based, C- and X-band Doppler radars; mobile and deployable surface sensors; unmanned aircraft systems; etc.) and standard operational observations to initialize cloud and mesoscale models using a variety of assimilation techniques, to enhance analyses and diagnostic studies of mesoscale processes, and to better establish the predictability of tornadic and other severe convective events up to 18 h in advance. Post-storm dropsondes will also be used to document the feedbacks of such storms on the larger-scale environment. Although VORTEX2 is being proposed for both the 2009 and 2010 seasons, dropsondes are being requested to support only the 2009 field campaign, in order to limit total experiment costs. Two MGAUS units are being requested for both 2009 and 2010. 2. Background VORTEX2 is a multi-agency field program to investigate tornadic storms and their environments, to take place in the United States Great Plains during the months of April-June, 2009-2010. It will be conducted as a two-phase experiment. A “tethered” phase (“phase A”), utilizing an adaptable observing network tethered to fixed observing facilities in Oklahoma (Fig. 2.1.a), will occur 1 April – 10 May each year, focusing on storm-environment interactions, storm-storm interactions. A “fully mobile” phase (“phase B”) will take place 11 May – 25 June each year over a broad region of the central United States (Fig. 2.1.b), focusing on tornadogenesis and tornado wind fields. Briefly, the four foci of VORTEX2 are: Relationships between supercell storms and their environments. Interactions among storms that are/are not favorable for tornadogenesis; effects of environmental heterogeneity on supercells and tornadogenesis; feedbacks of supercells upon their environments. Storm-scale and regional-scale numerical weather prediction (NWP). Analysis and prediction of supercells, mesocyclones, and tornadoes; assessment of parameterization errors for storm-scale models and data assimilation methods for the storm scale; optimal use of observations; analysis and prediction of the pre- storm mesoscale environment. Tornadogenesis. Role of downdrafts in tornadogenesis; sensitivity of tornadogenesis to microphysical and thermodynamic characteristics; role of vorticity maxima along gust fronts in tornadogenesis and/or maintenance; modes for the development of significant tornadoes in supercells. 2 Near-ground wind field in tornadoes. Range of observed tornado characteristics, such as vertical, radial, and swirling velocity profiles, asymmetries, multiple vortices, and angular momentum budgets; relationships between damage and wind speed, acceleration, and duration. These scientific foci address national research priorities in multiple ways. First, VORTEX2 research will contribute to basic understanding of convective storms, particularly interactions between cloud dynamical and microphysical processes. Second, VORTEX2 datasets will become a research testbed for regional-scale and storm-scale prediction experiments. It is generally believed that numerical weather prediction must play a prominent role in the National Weather Service (NWS) initiative to increase severe weather and tornado warning lead time. Unprecedented multi-sensor and multi-scale observations will be available for model initialization and forecast verification, enabling one to determine the optimal mix of observations, adaptive observing strategies, data-assimilation methods, and forecast models needed for successful storm-scale numerical weather prediction in future operational systems. In order to support VORTEX2 objectives, a host of mobile observing systems are being proposed (Table 2.1), including seven mobile, ground-based Doppler radars (C-band, X-band, and W-band radars, some of which will have dual-polarization and “rapid scan” capabilities); mobile soundings; a mobile mesonet; unmanned aircraft systems (UAS); and stick net (an array of surface sensors on tripods). The operational observing network, which includes WSR-88Ds (one or more of which could have polarimetric upgrades by the start of VORTEX2), rawinsondes, profilers, and surface sensors, will provide supporting environmental and storm-scale data. In addition, the tethered phase of VORTEX2 will utilize an extensive fixed observing network in Oklahoma: the National Weather Radar Testbed Phased Array Radar (NWRT-PAR), a prototype dual-polarization WSR-88D (KOUN), the Center for Collaborative Adaptive Sensing of the Atmosphere (CASA) radar network, the Kessler Farm Field Laboratory, the Oklahoma Mesonet, and ARS Micronets. Mobile soundings are essential to the success of VORTEX2, particularly for the foci on mesoscale environmental variability, regional- and storm-scale data assimilation and numerical weather prediction, storm-environment feedbacks, and tornadogenesis. The motivation for mobile soundings is provided in more detail in the following subsections. Science focus Required observing systems Phase Relationships Fixed observing systems (including NWRT-PAR and S-band A (tethered) between supercells radars), C-band and X-band mobile radars (at least two of which and their have dual polarization and one of which has “rapid scan” environments capability), mobile soundings, mobile mesonet, stick net, UAS Storm-scale NWP Fixed observing systems (including NWRT-PAR and S-band A (tethered) radars), C-band and X-band mobile radars (at least two of which have dual polarization and one of which has “rapid scan” capability), mobile soundings, mobile mesonet, stick net, UAS Tornadogenesis C-band and X-band mobile radars, mobile mesonet, stick net, B (fully mobile) mobile soundings, UAS, photogrammetry Near-ground wind X-band and W-band mobile radars, tornado in situ sensors, B (fully mobile) field in tornadoes photogrammetry, damage surveys Table 2.1. Core instruments proposed for VORTEX2. Other instruments, not included in this table, could be available, depending on the success of individual proposals. 3 Figure 2.1. Proposed domains for the (a) tethered (1 April – 10 May, 2009 and 2010) and (b) fully mobile (11 May – 25 June, 2009 and 2010) phases of VORTEX2. A. Mesoscale environmental variability Previous studies have identified significant environmental variability on multiple scales in the environments of convective storms (Maddox et al. 1980; Marwitz and Burgess 1994; Brooks et al. 1994, 1996; Weckwerth et al. 1996; Markowski et al. 1998a; Rasmussen et al. 2000; Markowski and Richardson 2004). These studies make it clear that the environment of a convective storm cannot be represented by a single sounding and highlight difficulties in relating observed storm behavior to predictions based on numerical parameter- space studies, which typically employ idealized, homogeneous environments (Brooks et al. 1994; Weisman et al. 1998; Richardson 1999; Richardson et al. 2007). The 2 June 1995 case during VORTEX1 (Fig. 2.2; Rasmussen et al. 1994, 2000; Gilmore and Wicker 2002) demonstrates clearly the potential impact of such mesoscale variability on supercell formation and subsequent tornadogenesis. This case featured numerous convective storms on both sides of a remnant outflow boundary that had been produced by convection many hours earlier. Among approximately 20 long- lived storms, the only storms that produced tornadoes
Details
-
File Typepdf
-
Upload Time-
-
Content LanguagesEnglish
-
Upload UserAnonymous/Not logged-in
-
File Pages25 Page
-
File Size-