Non-Rayleigh signal statistics in clustered statistically homogeneous rain

As the sample volume of a remote sensing instrument moves through sufficiently variable conditions, recent work shows that the amplitudes and associated intensities can deviate significantly at times from expectations based on Rayleigh signal statistics because fluctuations in the number of scatterers leads to a doubly stochastic measurement process. While non-Rayleigh deviations yield average biases for both logarithmic and linear detectors, perhaps of greater importance is the enhancement of the variance of the bias distribution for square law detectors. In this work the authors explore the potential existence of non-Rayleigh effects even in the statistically homogeneous rain when fluctuations in the number of scatterers should be much less than for the inhomogeneous conditions used in earlier studies. Moreover, in contrast to previous work, recent advances now permit the simulation of correlated rainfall structures having the statistical characteristics of natural rain such as clustering intensity (ℵ) and coherence length (χ) consistent with observations. The primary objective of this work, then, is to clarify how ℵ, χ, and the geometric parameters characteristic of remote sensing observations such as the distance over which an estimate is made (L), the beamwidth (B), and the spatial displacement between successive independent samples (Δ) affect non-Rayleigh signals statistics in statistically homogeneous rain. This work shows that non-Rayleigh effects can appear whenever Δ ⩽ χ ⩽ L. Moreover, the magnitudes of the non-Rayleigh deviations increase as ℵ and Δ/B increase. Although non-Rayleigh effects can be detected by monitoring of the signals, keeping both Δ/B and L as small as possible while increasing sample independence using chirp or signal whitening techniques, for example, should help to minimize non-Rayleigh effects for radars even in statistically inhomogeneous rain

Floods Forecast in the Caribbean

Floods are one of the most costly natural disasters in the world and represent a common hazard in Puerto Rico. Some floods develop slowly, sometimes over a period of a day or more. But flash floods can develop quickly, sometimes in just a few minutes. Puerto Rico, as well as other islands in the Caribbean, is subjected to flooding due to geographical location, topography, population distribution, and sudden rainfall events. The use of new technologies, such as apps and radars with higher spatial resolution that can cover areas missed by the NEXRAD radar, is important for flood forecasting efforts and for studying and predicting atmospheric phenomena. Recently, researchers in Puerto Rico initiated investigations using new technologies with high temporal and spatial resolution radars and systems that are able to monitor sudden floods in populated areas. These technologies will be used for hydrologic analyses and, specifically, for rainfall forecasting in Puerto Rico. A number of observational studies have shown that individual convective cells have mean lifetimes of about 20 min, with the best performance associated with a lead time of 10 min

Middle Atmosphere Program. Handbook for MAP, volume 28

Extended abstracts from the fourth workshop on the technical and scientific aspects of MST (mesosphere stratosphere troposphere) radar are presented. Individual sessions addressed the following topics: meteorological applications of MST and ST radars, networks, and campaigns; dynamics of the equatorial middle atmosphere; interpretation of radar returns from clear air; techniques for studying gravity waves and turbulence; intercomparison and calibration of wind and wave measurements at various frequencies; progress in existing and planned MST and ST radars; hardware design for MST and ST radars and boundary layer/lower troposphere profilers; signal processing; and data management

Hydrometeorological Extremes and Its Local Impacts on Human-Environmental Systems

This Special Issue of Atmosphere focuses on hydrometeorological extremes and their local impacts on human–environment systems. Particularly, we accepted submissions on the topics of observational and model-based studies that could provide useful information for infrastructure design, decision making, and policy making to achieve our goals of enhancing the resilience of human–environment systems to climate change and increased variability

Interaction of the terrestrial and atmospheric hydrological cycles in the context of the North American southwest summer monsoon

Work under this grant has used information on precipitation and water vapor fluxes in the area of the Mexican Monsoon to analyze the regional precipitation climatology, to understand the nature of water vapor transport during the monsoon using model and observational data, and to analyze the ability of the TRMM remote sensing algorithm to characterize precipitation. An algorithm for estimating daily surface rain volumes from hourly GOES infrared images was developed and compared to radar data. Estimates were usually within a factor of two, but different linear relations between satellite reflectances and rainfall rate were obtained for each day, storm type and storm development stage. This result suggests that using TRMM sensors to calibrate other satellite IR will need to be a complex process taking into account all three of the above factors. Another study, this one of the space-time variability of the Mexican Monsoon, indicate that TRMM will have a difficult time, over the course of its expected three year lifetime, identifying the diurnal cycle of precipitation over monsoon region. Even when considering monthly rainfalls, projected satellite estimates of August rainfall show a root mean square error of 38 percent. A related examination of spatial variability of mean monthly rainfall using a novel method for removing the effects of elevation from gridded gauge data, show wide variation from a satellite-based rainfall estimates for the same time and space resolution. One issue addressed by our research, relating to the basic character of the monsoon circulation, is the determination of the source region for moisture. The monthly maps produced from our study of monsoon variability show the presence of two rainfall maxima in the analysis normalized to sea level, one in south-central Arizona associated with the Mexican monsoon maximum and one in southeastern New Mexico associated with the Gulf of Mexico. From the point of view of vertically-integrated fluxes and flux divergence of water vapor from ECMWF data, most moisture at upper levels arrives from the Gulf of Mexico, while low level moisture comes from the northern Gulf of California. Composites of ECMWF analyses for wet and dry periods (classified by rain gauge data) show that both regimes show low level moisture arriving from northern and central Gulf of California. Above 700 MB, moisture comes from both source regions and the Sierra Madre Occidental. During wet periods a longer fetch through the moist air mass above western Mexico results in a greater moisture flux into the Sonoran Desert region, while there is less moisture from the Gulf of Mexico both above and below 700 mb. Work on the grant subcontract at the University of Colorado concentrated on the development of a technique useful to TRMM combining visible, infrared and passive microwave data for measuring precipitation. Two established techniques using either visible or infrared data applied over the US Southwest correlated with gauges at the 0.58 to 0.70 level. The application of some established passive microwave techniques were less successful for a variety of reason, including problems in both the gauge and satellite data quality, sampling problems and weaknesses inherent in the algorithms themselves. A more promising solution for accurate rainfall estimation was explored using visible and infrared data to perform a cloud classification, which when combined with information about the background (e.g. Iand/ocean), was used to select the most appropriate microwave algorithm from a suite of possibilities

Wind Shear/Turbulence Inputs to Flight Simulation and Systems Certification

The purpose of the workshop was to provide a forum for industry, universities, and government to assess current status and likely future requirements for application of flight simulators to aviation safety concerns and system certification issues associated with wind shear and atmospheric turbulence. Research findings presented included characterization of wind shear and turbulence hazards based on modeling efforts and quantitative results obtained from field measurement programs. Future research thrusts needed to maximally exploit flight simulators for aviation safety application involving wind shear and turbulence were identified. The conference contained sessions on: Existing wind shear data and simulator implementation initiatives; Invited papers regarding wind shear and turbulence simulation requirements; and Committee working session reports

Study of thunderstorm wind outflows and proposition of mean wind profiles

The impact of thunderstorm (TS) winds on the built environment has been extensively reported in recent years showing that current wind standards do not properly represent all types of extreme wind events. This document discusses the characteristics of TS winds in depth, focusing on existing vertical full-scale measurements, modeling approaches and their occurrence worldwide. Firstly, the development of the downburst research worldwide is reviewed and, due to Brazil’s vulnerability to this type of event, reported cases in national news and scientific literature are investigated. This study showed that most of Brazil is vulnerable to downbursts, having the Amazon region the larger amount of occurrences and the Southern states the most susceptible for extreme winds generated by TS outflows or simply downbursts. The Southeastern states are also prone to extreme downburst occurrence. Northeast and central north states present downburst events with lower intensity, which are caused mostly by isolated thunderstorms. Modeling techniques are commonly adopted to study the effects of these events on the built environment. A systematic review of 122 publications on downburst modeling identified four main clusters of alternative approaches to simulating these events: analytical modeling, experimental laboratory simulations, computer fluid dynamics (CFD) and data-driven models. An analytical method is proposed to describe the mean wind speed profiles at their maximum stage based on full-scale measurements considering the storm organization, time averaging and terrain categories. The proposed fitted curve profile functions are valid only for the original measured average intervals. Results showed that most of the proposed fitted curve profile functions had a "nose-like" shape, highly defined by the terrain roughness, with peak velocities typically observed at lower levels in TS winds – between 50 and 250 meters – allowing the profile fitting by a third‐degree polynomial function, instead of the traditional power law function as adopted for synoptic winds. Seventeen profiles originated from full-scale measurements were selected and carefully analyzed. However, in order to propose a practical application that can be coupled with a general extreme wind climatology, only seven fitted curve profile functions were taken for further analysis. Six out of seven fitted curve profiles demonstrated good adherence to Ponte Junior (2005) model and the TS wind profile proposed by the international code ISO 4354. These proposed profiles were further analyzed along with the typical NBR-6123 boundary layer velocity profiles. For Terrain Category II, the fitted curve profile function based on the maximum profile of Gunter and Schroeder (2015) "PEP Event" for 1-min time averaging presented the most conservative case at all elevations. For Terrain Category III, results were mixed, but the fitted curve profile function based on the maximum profile measured by Lombardo et al. (2014) "03-Aug-2010 Event" presented maximum values at lower levels for 3-s time averaging and is therefore considered the maximum profile for this terrain category. Finally, for Category IV, it is suggested to use as reference the fitted curve profile based on the maximum profile of Zhang *et al.* (2019) "15:01 Meas.", since this is a more realistic TS wind profile dataset for 30-s time averaging due to the particular effects of the terrain on that specific measurement.O impacto dos ventos gerados por tempestades (TS) no ambiente construído tem sido amplamente relatado nos últimos anos, revelando que as normas de vento atuais não representam adequadamente todos os tipos de ventos extremos. Neste documento se discute em profundidade as características dos ventos TS, com foco em medições verticais de escala real, abordagens de modelagem e sua ocorrência no mundo. Primeiramente, é revisado o desenvolvimento mundial das pesquisas sobre downbursts e, devido à vulnerabilidade do Brasil a esse tipo de evento, é feita uma investigação de casos relatados em notícias e literatura científica. Este estudo mostrou que a maior parte do Brasil é extremamente vulnerável a downbursts, tendo a região Amazônica o maior número de ocorrências e os estados da região Sul os mais suscetíveis a ventos extremos gerados por tormentas TS ou simplesmente downbursts. Os estados do Sudeste são também propensos à ocorrência de downbursts severos. Os estados do Nordeste e Centro-Norte apresentam eventos de menor intensidade, causados principalmente por tempestades isoladas. Técnicas de modelagem são comumente adotadas para estudar os efeitos desses eventos no ambiente construído. Uma revisão sistemática de 122 publicações sobre modelagem de downbursts identificou quatro grupos principais de abordagens para simular esses eventos: modelos analíticos, simulações experimentais em laboratório, dinâmica de fluidos computacional (CFD) e modelos baseados em dados. Um método analítico é proposto para descrever os perfis médios de velocidade de vento em seu estágio máximo com base em medições em escala real, considerando-se organização da tempestade, intervalo de tempo e categorias de terreno. As funções de perfil de curva ajustada propostas são válidas apenas para os intervalos de tempo medidos originais. Os resultados mostraram que a maioria das funções propostas de perfis de curvas ajustadas tinham forma de "nariz", fortemente definida pela rugosidade do terreno e com velocidades de pico tipicamente observadas em níveis mais baixos em ventos TS – entre 50 e 250 metros – permitindo o ajuste do perfil por uma função polinomial de terceiro grau, em vez da função de potência tradicional, como utilizado para ventos sinóticos. Dezessete perfis oriundos de medições reais foram selecionados e analisados minuciosamente. Porém, para possibilitar a proposição de uma aplicação prática capaz de incorporar resultados de climatologias gerais de ventos extremos TS, somente sete curvas ajustadas foram levadas adiante para análise. Seis dos sete perfis ajustados demonstraram boa aderência ao modelo de Ponte Junior (2005) e ao perfil de vento TS proposto pelo código internacional ISO 4354. Esses perfis propostos foram posteriormente analisados juntamente com os perfis de velocidade de camada limite típicos da NBR-6123. Para a categoria de terreno II, a função do perfil ajustada com base nos valores máximos obtidos por Gunter e Schroeder (2015) no "PEP Event" para intervalo de tempo de 1-min apresentou o caso mais conservador em todas as elevações. Para a categoria de terreno III, os resultados foram mistos, mas considerou-se como evento extremo o perfil ajustado baseado no evento extremo de “03-ago-2010" de Lombardo et al. (2014) para o intervalo de média de tempo de 3-s. Finalmente, para a Categoria IV, sugere-se utilizar como referência o perfil de curva ajustado ao evento extremo registrado por Zhang et al. (2019) "15:01 Meas.", uma vez que o perfil de vento TS resultante é mais realista para média de tempo de 30-s devido aos efeitos do terreno específicos deste caso

Middle Atmosphere Program. Handbook for MAP. Volume 30: International School on Atmospheric Radar

Broad, tutorial coverage is given to the technical and scientific aspects of mesosphere stratosphere troposphere (MST) meteorological radar systems. Control issues, signal processing, atmospheric waves, the historical aspects of radar atmospheric dynamics, incoherent scatter radars, radar echoes, radar targets, and gravity waves are among the topics covered