Forcing mechanisms of thunderstorm downdrafts

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1991.Includes bibliographical references (p. 151-156).by Joshua Michael Aaron Ryder Wurman.Sc.D

The long range dispersion of radioactive particulates

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Meteorology and Physical Oceanography, 1982.Microfiche copy available in Archives and ScienceBibliography: leaves 194-196.by Joshua Michael Aaron Ryder Wurman.M.S

Wind Field of a Nonmesocyclone Anticyclonic Tornado Crossing the Hong Kong International Airport

A nonmesocyclone tornado traversed the Hong Kong International Airport on September 6, 2004 directly impacting a surface weather station. This allowed for 1-second 10-meter above ground level (AGL) wind observations through the core of the tornado. Integration of these 10-meter AGL wind data with Ground-Based Velocity Track (GBVTD) wind retrievals derived from LIDAR data provided a time history of the three-dimensional wind field of the tornado. These data indicate a progressive decrease in radial inflow with time and little to no radial inflow near the time the tornado crosses the surface weather station. Anemometer observations suggest that the tangential winds approximate a modified-Rankine vortex outside the radius of maximum winds, suggesting that frictionally induced radial inflow was confined below 10 m AGL. The radial-height distribution of angular momentum depicts an increase in low-level angular momentum just prior to the tornado reaching its maximum intensity

Aerial Damage Survey of the 2013 El Reno Tornado Combined with Mobile Radar Data

A detailed damage survey of the El Reno, Oklahoma, tornado of 31 May 2013 combined with rapid-scanning data recorded from two mobile radars is presented. One of the radars was equipped with polarimetric capability. The relationship between several suction vortices visually identified in pictures with the high-resolution Doppler velocity data and swath marks in fields is discussed. The suction vortices were associated with small shear features in Doppler velocity and a partial ringlike feature of high spectral width. For the first time, a suction vortex that created a swath mark in a field was visually identified in photographs and high-definition video while the rotational couplet was tracked by radar. A dual-Doppler wind synthesis of the tornadic circulation at low levels near the location of several storm chaser fatalities resolved ground-relative wind speeds in excess of 90 m s−1, greater than the minimum speed for EF5 damage. The vertical vorticity analysis revealed a rapid transition from a single tornadic vortex centered on the weak-echo hole (WEH) to suction vortices surrounding the WEH and collocated with the ring of enhanced radar reflectivities. Several bands/zones of enhanced convergence were resolved in the wind syntheses. One of the bands was associated with an internal or secondary rear-flank gust front. An inner band of convergence appeared to be a result of the positive bias in tornado-relative radial velocity owing to centrifuging of large lofted debris swirling within the tornado. An outer band of convergence formed at the northern edge of a region of strong inflow that was lofting small debris and dust into the storm

The 2015 Plains Elevated Convection at Night Field Project

The central Great Plains region in North America has a nocturnal maximum in warm-season precipitation. Much of this precipitation comes from organized mesoscale convective systems (MCSs). This nocturnal maximum is counterintuitive in the sense that convective activity over the Great Plains is out of phase with the local generation of CAPE by solar heating of the surface. The lower troposphere in this nocturnal environment is typically characterized by a low-level jet (LLJ) just above a stable boundary layer (SBL), and convective available potential energy (CAPE) values that peak above the SBL, resulting in convection that may be elevated, with source air decoupled from the surface. Nocturnal MCS-induced cold pools often trigger undular bores and solitary waves within the SBL. A full understanding of the nocturnal precipitation maximum remains elusive, although it appears that bore-induced lifting and the LLJ may be instrumental to convection initiation and the maintenance of MCSs at night. To gain insight into nocturnal MCSs, their essential ingredients, and paths toward improving the relatively poor predictive skill of nocturnal convection in weather and climate models, a large, multiagency field campaign called Plains Elevated Convection At Night (PECAN) was conducted in 2015. PECAN employed three research aircraft, an unprecedented coordinated array of nine mobile scanning radars, a fixed S-band radar, a unique mesoscale network of lower-tropospheric profiling systems called the PECAN Integrated Sounding Array (PISA), and numerous mobile-mesonet surface weather stations. The rich PECAN dataset is expected to improve our understanding and prediction of continental nocturnal warm-season precipitation. This article provides a summary of the PECAN field experiment and preliminary findings

2009: Polarimetric and dual-Doppler radar observations of the Lipscomb County

ABSTRACT Polarimetric and dual-Doppler observations of a supercell observed by the National Center for Atmospheric Research (NCAR) S-band Polarimetric (SPOL) radar, two Doppler-On-Wheels (DOW) radars, and the Greek XPOL radar on 23 May 2002 during the International H 2 O Project (IHOP) are presented. The polarimetric radar observations began as the storm organized into a supercell and continued for over an hour while the storm was in its mature phase. The hydrometeor distribution within the mature storm was retrieved using a fuzzy logic hydrometeor classification algorithm. The dual-Doppler radar observations began around the time that the polarimetric radar observations concluded, and they covered the end of the mature phase and much of the dissipation phase of the storm. The dual-Doppler wind syntheses are used to evaluate the importance of the forward-flank outflow in augmenting the horizontal vorticity field near the storm above 400 m. In this case, having a relatively weak low-level mesocyclone, the parcel trajectories and the horizontal vorticity field observed within the forward-flank outflow are not what one would likely expect based on prior numerical studies (having generally stronger low-level mesocyclones) that have emphasized an important dynamical role for forward-flank downdrafts in terms of their horizontal vorticity generation. Instead, the observed trajectories could not be traced from the forward-flank outflow toward the storm's updraft and the horizontal vorticity vectors within the forward-flank outflow generally did not point (westward) toward the storm's updraft

The Great Plains Irrigation Experiment (GRAINEX)

Extensive expansion in irrigated agriculture has taken place over the last half century. Due to increased irrigation and resultant land use land cover change, the central United States has seen a decrease in temperature and changes in precipitation during the second half of 20th century. To investigate the impacts of widespread commencement of irrigation at the beginning of the growing season and continued irrigation throughout the summer on local and regional weather, the Great Plains Irrigation Experiment (GRAINEX) was conducted in the spring and summer of 2018 in southeastern Nebraska. GRAINEX consisted of two, 15-day intensive observation periods. Observational platforms from multiple agencies and universities were deployed to investigate the role of irrigation in surface moisture content, heat fluxes, diurnal boundary layer evolution, and local precipitation. This article provides an overview of the data collected and an analysis of the role of irrigation in land-atmosphere interactions on time scales from the seasonal to the diurnal. The analysis shows that a clear irrigation signal was apparent during the peak growing season in mid- July. This paper shows the strong impact of irrigation on surface fluxes, near-surface temperature and humidity, as well as boundary layer growth and decay