The 16 April 2011 EF3 Tornado in Greene County, Eastern North Carolina

This paper presents a case study of an EF3 tornado that adversely impacted Greene and Pitt Counties in eastern North Carolina on 16 April 2011. This was one of the most damaging and longest-lived of the multiple tornados that occurred across central and eastern North Carolina that day, the most extensive outbreak in North Carolina since 1984. This event occurred during the month (April 2011) with the largest number of tornadoes on record in the United States. The focus of this case study was to examine the relationship between the mesocyclone evolution and the location and intensity of surface damage associated with the EF3 tornado. Results indicated that the initial contraction and spin up of the mesocyclone circulation preceded EF3 damage by about 20 minutes. At the time of mesocyclone intensification, the damage swath and tornado were situated much closer to the mesocyclone center than in the formative and dissipating stages. The weakened mesocyclone passed directly over a meteorological station at East Carolina University’s West Research Campus, providing a rare opportunity for surface measurements associated with a weakening tornadic mesocyclone

Convection in TOGA COARE: horizontal scale, morphology, and rainfall production

November 1996.Also issued as author's dissertation (Ph.D.) -- Colorado State University, 1996.Includes bibliographical references.Shipboard radar data collected during the recent Tropical Oceans - Global Atmospheres Coupled Ocean - Atmosphere Response Experiment (TOGA COARE) provided an unprecedented view of convection in the western Pacific warm pool, a region of global climatological significance. Previous studies have shown that the vertical transport of heat and momentum by convection differs with the scale and organization of precipitating systems. The relative importance of these transports by mesoscale convective systems (MCS) versus smaller groups of convective clouds over the tropical oceans is not well understood. The goal of this study is to understand the variability of warm pool rainfall production in terms of the horizontal scale and morphology of convective systems. This variability is examined in the context of the kinematic and thermodynamic state of the environment. Furthermore, high frequency convective variability (1-5 days) is studied in detail. It is found that although most of the rainfall is associated with MCS scale systems, unorganized isolated convection was most common and produces a significant fraction of the total rainfall. Although MCS scale heating dominated the COARE mean, distinct sub-MCS scale events heating occurred more frequently. Environmental moisture profiles distinguished between modes of convective organization more clearly than wind profiles. Furthermore, the weak diurnal variation of rainfall was found to result from the superposition of stronger, distinct diurnal rainfall variability associated with each mode of organization. These results are important to the refinement of convective parameterizations in global climate models.Sponsored by the National Oceanic and Atmospheric Administration under grant NA90RAH00077 and NA37J0202

Mechanisms for Springtime Onset of Isolated Precipitation across the Southeastern United States

This study uses four-year radar-based precipitation organization and reanalysis datasets to study the mechanisms that lead to the abrupt springtime onset of precipitation associated with isolated storms in the Southeast United States (SE US). Although the SE US receives relatively constant precipitation year-round, previous work demonstrated a “hidden” summertime maximum in isolated precipitation features (IPF) whose annual cycle resembles that of monsoon climates in the subtropics. In the SE US, IPF rain abruptly ramps up in May and lasts until sometime between late August and early October. This study suggests that the onset of the IPF season in the SE US is brought about by a combination of slow thermodynamic processes and fast dynamic triggers, as follows. First, in the weeks prior to IPF onset, a gradual seasonal build-up of convective available potential energy (CAPE) occurs in the Gulf of Mexico. Then, in one-to-two pentads prior to onset, the upper-tropospheric jet stream shifts northward, favoring the presence of slow-moving frontal systems in the SE US. This poleward shift in the jet stream location in turn allows the establishment of the North Atlantic subtropical high western ridge over the SE US which, with associated poleward transport of high CAPE air from the Gulf of Mexico, leads to the establishment of the warm-season regime of IPF precipitation in the SE US

Influencia del Anticiclón del Atlántico Norte en la pluviosidad de la brisa marina en Carolina del Norte, Estados Unidos

The sea-breeze (SB) is an important source of summertime precipitation in North Carolina (NC, southeast United States). However, not all SB events produce precipitation. A climatology of wet and dry SB events in NC is used to investigate the conditions that are conducive to precipitation associated with the sea breeze. Radar imagery was used to detect 88 SB events that occurred along the NC coast between May-September of 2009-2012. The majority (85%) of SB events occurred during offshore flow (53%) or during flow that was parallel to the coast (22%). SB events were separated into dry (53%) and wet (47%) events and differences in the dynamic and thermodynamic parameters of the environment in which they formed were analyzed. Significant differences in dynamic and thermodynamic conditions were found. SB dry events occurred under stronger winds (6.00 ± 2.36 ms-1) than SB wet events (4.02 ± 2.16 ms-1). Moreover, during SB wet events larger values of convective available potential energy and lower values of convective inhibition were present, conditions that favor precipitation. Overall, the SB wet events accounted for 20-30% of the May-September precipitation along the NC coastal region. The position of the North Atlantic Subtropical High (NASH) controls both moisture availability and winds along the NC coast, thus providing a synoptic-scale control mechanism for SB precipitation. In particular, it was shown that when the NASH western ridge is located along the southeast coast of the United States, it causes a moist southwesterly flow along the NC coast that may favor the occurrence of SB wet events.La brisa marina (BM) es una importante fuente de precipitación de verano en Carolina del Norte (NC en su sigla en inglés), sudeste de Estados Unidos. Sin embargo, no todos los eventos de BM producen precipitación. En este trabajo se utiliza una climatología de eventos de BM lluviosos y secos en NC para investigar las condiciones que conducen a la precipitación. Se utilizaron imágenes de radar para detectar 88 eventos de BM ocurridos a lo largo de la costa NC entre mayo y septiembre de 2009 a 2012. La mayoría (85%) de los eventos de BM ocurrieron durante períodos de viento hacia el mar (53%) o viento paralelo a la costa (22%). Los eventos BM se separaron en eventos secos (53%) y lluviosos (47%) y se analizaron las diferencias en los parámetros dinámicos y termodinámicos del entorno en el que se formaron. Se encontraron diferencias significativas en las condiciones dinámicas y termodinámicas. Eventos de BM secos ocurrieron bajo vientos más fuertes (6,00 ± 2,36 ms-1) que los eventos de BM lluviosos (4,02 ± 2,16 ms-1). Las BM lluviosas ocurrieron bajo valores de energía potencial convectiva disponible más altos y valores del parámetro de inhibición convectiva más bajos, condiciones que favorecen la lluvia. En general, los eventos de BM lluviosos representaron el 20-30% de la precipitación a lo largo de la región costera de NC de mayo a septiembre. La posición de la Alta Subtropical del Atlántico Norte (ASAN) controla la disponibilidad de humedad y los vientos a lo largo de la costa de NC, proporcionando así un mecanismo de control de escala sinóptica para la precipitación de la BM. En particular, cuando la cresta occidental de la ASAN se localiza a lo largo de la costa sureste de los Estados Unidos, se produce un flujo de sudoeste húmedo a lo largo de la costa NC que puede favorecer la ocurrencia de eventos de BM lluviosos.This project was partially funded by the Climate and Large-Scale Dynamics and the Physical and Dynamic Meteorology programs of the National Science Foundation’s Division of Atmospheric and Geospatial Sciences, Award AGS-1118141

Automated snow avalanche release area delineation – validation of existing algorithms and proposition of a new object-based approach for large-scale hazard indication mapping

Snow avalanche hazard is threatening people and infrastructure in all alpine regions with seasonal or permanent snow cover around the globe. Coping with this hazard is a big challenge and during the past centuries, different strategies were developed. Today, in Switzerland, experienced avalanche engineers produce hazard maps with a very high reliability based on avalanche database information, terrain analysis, climatological data sets and numerical modeling of the flow dynamics for selected avalanche tracks that might affect settlements. However, for regions outside the considered settlement areas such area-wide hazard maps are not available mainly because of the too high cost, in Switzerland and in most mountain regions around the world. Therefore, hazard indication maps, even though they are less reliable and less detailed, are often the only spatial planning tool available. To produce meaningful and cost-effective avalanche hazard indication maps over large regions (regional to national scale), automated release area delineation has to be combined with volume estimations and state-of-the-art numerical avalanche simulations.In this paper we validate existing potential release area (PRA) delineation algorithms, published in peer-reviewed journals, that are based on digital terrain models and their derivatives such as slope angle, aspect, roughness and curvature. For validation, we apply avalanche data from three different ski resorts in the vicinity of Davos, Switzerland, where experienced ski-patrol staff have mapped most avalanches in detail for many years. After calculating the best fit input parameters for every tested algorithm, we compare their performance based on the reference data sets. Because all tested algorithms do not provide meaningful delineation between individual PRAs, we propose a new algorithm based on object-based image analysis (OBIA). In combination with an automatic procedure to estimate the average release depth (d0), defining the avalanche release volume, this algorithm enables the numerical simulation of thousands of avalanches over large regions applying the well-established avalanche dynamics model RAMMS. We demonstrate this for the region of Davos for two hazard scenarios, frequent (10–30-year return period) and extreme (100–300-year return period). This approach opens the door for large-scale avalanche hazard indication mapping in all regions where high-quality and high-resolution digital terrain models and snow data are available.</p

Discontinuation of primary prophylaxis against Pneumocystis carinii pneumonia in HIV-1-infected adults treated with combination antiretroviral therapy. Swiss HIV Cohort Study

BACKGROUND: It is unclear whether primary prophylaxis against Pneumocystis carinii pneumonia can be discontinued in patients infected with the human immunodeficiency virus (HIV) who are successfully treated with combination antiretroviral therapy. We prospectively studied the safety of stopping prophylaxis among patients in the Swiss HIV Cohort Study. METHODS: Patients were eligible for our study if their CD4 counts had increased to at least 200 cells per cubic millimeter and 14 percent of total lymphocytes while they were receiving combination antiretroviral therapy, with these levels sustained for at least 12 weeks. Prophylaxis was stopped at study entry, and patients were examined every three months thereafter. The development of P. carinii pneumonia was the primary end point, and the development of toxoplasmic encephalitis the secondary end point. RESULTS: Of the 262 patients included in our analysis, 121 (46.2 percent) were positive for IgG antibodies to Toxoplasma gondii at base line. The median CD4 count at study entry was 325 per cubic millimeter (range, 210 to 806); the median nadir CD4 count was 110 per cubic millimeter (range, 0 to 240). During a median follow-up of 11.3 months (range, 3.0 to 18.8), prophylaxis was resumed in nine patients, and two patients died. There were no cases of P. carinii pneumonia or toxoplasmic encephalitis. The one-sided upper 99 percent confidence limit for the incidence of P. carinii pneumonia was 1.9 cases per 100 patient-years (based on 238 patient-years of follow-up). The corresponding figure for toxoplasmic encephalitis was 4.2 per 100 patient-years (based on 110 patient-years of follow-up). CONCLUSIONS: Stopping primary prophylaxis against P. carinii pneumonia appears to be safe in HIV-infected patients who are receiving combination antiretroviral treatment and who have had a sustained increase in their CD4 counts to at least 200 cells per cubic millimeter and to at least 14 percent of total lymphocytes