This study investigates the energy spectrum of electron microbursts observed by the Focused Investigations of Relativistic Electron Burst Intensity, Range, and Dynamics II (FIREBIRD‐II, henceforth ...FIREBIRD) CubeSats. FIREBIRD is a pair of CubeSats, launched in January 2015 into a low Earth orbit, which focuses on studying electron microbursts. High‐resolution electron data from FIREBIRD‐II consist of 5 differential energy channels between 200 keV and 1 MeV and a >1 MeV integral channel. This covers an energy range that has not been well studied from low Earth orbit with good energy and time resolution. This study aims to improve the understanding of the scattering mechanism behind electron microbursts by investigating their spectral properties and their relationship with the equatorial electron population under different geomagnetic conditions. Microbursts are identified in the region of the North Atlantic where FIREBIRD only observes electrons in the bounce loss cone. The electron flux and exponential energy spectrum of each microburst are calculated using a FIREBIRD instrument response modeled in GEANT4 (GEometry ANd Tracking) and compared with the near‐equatorial electron spectra measured by the Van Allen Probes. Microbursts occurring when the Auroral Electrojet (AE) index is enhanced tend to carry more electrons with relatively higher energies. The microburst scattering mechanism is more efficient at scattering electrons with lower energies; however, the difference in scattering efficiency between low and high energy is reduced during periods of enhanced AE.
Key Points
We present a statistical study of the energy spectrum of electron microbursts observed by the FIREBIRD‐II CubeSats
Individual microbursts contain more electrons at a higher Auroral Electrojet as well as relatively more high‐energy electrons
The microburst scattering mechanism is more efficient at scattering low‐energy electrons
Microbursts are meteorological phenomena in the lower troposphere which can produce damaging surface winds and pose a severe risk to aircraft flying close to the ground. As these events usually span ...less than 4 km and 15 min, the spatiotemporal resolution is a challenge for numerical simulations. Although research of microburst using operative mesoscale models is scarce, the Weather Research and Forecasting (WRF) model has been used in the diagnosis of this phenomenon. In this paper, such model is used to simulate several microburst conducive days using two different boundary conditions. The energy spectra of the simulations are computed to evaluate the effective resolution of the model. The results are in line with previous studies and produce no notable differences among the boundary conditions. Nonetheless, the energy spectra show an overenergetic troposphere at microscale resolutions, rendering the effective resolution inadequate for microburst forecasting using the simulated physics variables. Thus, mesoscale indices are analyzed as a prognostic tool. The wind index, the wet microburst severity index and the microburst windspeed potential index do not show high forecasting performances, even though improving the results of climatology. Also, notable differences among the boundary conditions can be seen. The most consistent results are achieved by the wet microburst severity index.
Key Points
The WRF model shows an unrealistic energy spectrum when microscale spatial resolutions are used
The effective resolution of the simulations casts doubts over the ability to forecast microbursts
WINDEX, WMSI, and MWPI microburst indices show better forecasting performance than climatology, despite being suboptimal in general terms
In the present study, an experimental investigation is conducted to quantify the characteristics of the microburst-induced wind loads (i.e., both static and dynamic wind loads) acting on a high-rise ...building model, compared to those with the test model placed in conventional atmospheric boundary layer (ABL) winds. The experimental study is performed by using an impinging-jet-based microburst simulator available at Iowa State University. In additional to conducting flow field measurements to quantify the flow characteristics of the microburst-like wind, both mean and dynamic wind loads acting on the test model induced by the microburst-like wind are assessed in detail based on the quantitative measurements of the surface pressure distributions around the test model and the resultant aerodynamic forces. It is found that the microburst-induced wind loads acting on high-rise buildings would be significantly different from their counterparts in conventional ABL winds. Both the static and dynamic wind loads acting on the high-rise building model were found to change significantly depending on the radial locations and the orientation angles of the test model in respect to the oncoming microburst-like wind. The dynamic wind loads acting on the test model were found to be mainly influenced by the periodical shedding of the primary vortices and the high turbulence levels in the microburst-like wind. The findings derived from the present study are believed to be useful to gain further insight into the underlying physics of the flow–structure interactions of high-rise buildings in violent microburst winds for a better understanding of the damage potential of microburst winds to high-rise buildings.
Atmospheric microbursts are low‐level meteorological events that can produce significant damage on the surface and pose a major risk to aircraft flying close to the ground. Studies and ad hoc ...numerical models have been developed to understand the origin and dynamics of the microburst; nevertheless, there are few researches of the phenomenon using global and mesoscale models. This is mainly due to the limitations in resolution, as microbursts normally span for less than 4 km and 20 min. In this paper, the Weather Research and Forecasting model is used at resolutions of 400 m and 3 min to test if it can properly capture the variables and dynamics of high‐reflectivity microbursts. Several microphysics and planetary boundary layer parametrizations are tested to find the best model configuration for the simulation of this kind of episodes. General conditions are evaluated by using thermodynamic diagrams. Surface and vertical wind speed, reflectivity, precipitation, and other variables for each simulated event are compared with observations, and the model's sensitivity to the variables is assessed. The dynamics and evolution of the microburst is evaluated using different plots of a chosen event. The results show that the model is able to reproduce high‐reflectivity microbursts in accordance with observations, although there is a tendency to underestimate the intensity of variables, most markedly on the wind vertical velocity. Regarding the microphysics schemes, the Morrison parametrization performs better than the WRF single‐moment 6‐class scheme. No major differences are found between the Mellor‐Yamada‐Janjic and the Mellor‐Yamada‐Nakanishi‐Niino planetary boundary layer parametrizations.
Key Points
The Weather Research and Forecasting numerical model is able to reproduce high‐reflectivity microbursts
The characteristic variables of the microburst are properly simulated, although some intensities are lower than observations
Differences are observed between different microphysics and planetary boundary layer parametrizations
Located at the southeastern coast of Guangdong Province of China, Hong Kong is susceptible to the effects of severe convective weather and tropical cyclones. The Hong Kong International Airport ...(HKIA) is susceptible to windshear and microbursts caused by convective weather. Due to the complex terrain around the HKIA, windshear caused by strong winds of tropical cyclones across complex terrain can be as strong as microbursts generated by thunderstorms. A Terminal Doppler Weather Radar (TDWR) has been used to detect microbursts and windshear in real time to safeguard aviation safety. The TDWR at Brothers Point, Tuen Mun, Hong Kong, was optimized to detect windshear and microbursts in a highly cluttered environment. Stationary and moving clutters were suppressed and radar velocity data were dealiased by the hybrid multiple pulse repetition interval method during radar system optimization. A case on October 4, 2015 showed that the TDWR performed satisfactorily with a probability of detection and a false alarm ratio of 91% and 1% respectively in detecting microbursts by comparing microburst features identified by the TDWR and human truth, which is a method to identify areas of interest by analysts.
Windshear caused by strong winds of tropical cyclones across the complex terrain of the Hong Kong International Airport can be as strong as thunderstorm‐related microbursts. A Terminal Doppler Weather Radar (TDWR) was used to detect microbursts and windshear. A case on October 4, 2015 showed that the TDWR performed satisfactorily with a probability of detection and a false alarm ratio of 91% and 1% respectively in detecting the microbursts by comparing microburst features identified by the TDWR and human truth.
This paper reports the first aero-elastic test conducted under a scaled downburst wind field at the WindEEE dome facility at the University of Western Ontario, Canada. The main purpose of the test is ...to assess the dynamic response of a multi-span transmission line. The study starts by providing a characterization of the downburst wind field produced in WindEEE including a comparison with results of previously conducted numerical simulations. A number of test configurations, involving different locations of the downburst relative to the line, is considered. A decomposition approach is developed to separate between the resonant and the background components of the response. The results are presented in the form of a dynamic magnification factor that relates the peak response including the dynamic effect to the maximum quasi-static response. The test results show that the resonance contribution ranges between 5% and 10% of the peak response for the tower. They also show that the dynamic response of the conductors can reach up to 30% and 12% of the peak response at low and high downburst speeds, respectively.
•The dynamic response of a transmission line structure subjected to simulated downburst wind field is assessed.•A number of six towers are simulated according to scale 1:50.•A downburst of 3.2 m diameter is simulated at the WindEEE dome.•Different downburst wind angles are considered.
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•Windstorm effects on vegetation, soil chemistry, microbiota, and microclimate were tested.•Windstorm disturbance increased the abundance of plant invasive species during ...regeneration.•Windstorm decreased OC and total N contents while increased pH and P content.•The storm increased light and caused variations in air temperature and relative humidity.•The storm disturbance increased soil bacterial and fungal species richness and diversity.
We investigated the effects of a severe windstorm on vegetation, soil chemistry, understory microclimate, and soil microbiota in a Mediterranean holm oak forest. Plant species composition remained almost unchanged in the undisturbed area, whereas highly diverse plant communities were found in the disturbed area (e.g. gap area). Specifically, 11 invasive plant species were detected in 2015, but four years after, five disappeared and another five decreased, with only Ailanthus altissima increasing. Soil in disturbed areas has higher pH, Na, P, K, Ca, Cu, and Mn, but lower total limestone, organic carbon, total nitrogen, Mg, Fe, and standing litter compared to undisturbed areas. Disturbed areas had higher light availability at the ground and large variations in soil and air temperature and air relative humidity compared to undisturbed areas. The storm disturbance increased soil bacterial and fungal species richness and diversity. Moreover, the microbial co-occurrence network in the undisturbed area was more heterogeneous and complex, while modularity and number of positive correlations were higher in the disturbed area, which suggests that the structural composition of microbial communities and their co-occurrence patterns have been altered by windstorm disturbance. In the gaps, soil microbial community composition indicated a shift toward an opportunistic microbiota dominated by fast-growing but less competitive species. In addition, we found a large increase in putative plant pathogens but a decrease in simbiotrophic and ectomycorrhizal fungi in the gaps. The present work demonstrate the multiple effects of storm damage on the above- and belowground structure and diversity of forest ecosystems.
Abstract
The impact of low-level wind shear (LLWS) is still a critical issue in aviation. These days, as the aviation industry grows, it must follow safety improvement efforts and transportation ...management, one of which is through the accurate publishing of LLWS early warning. Therefore, it takes a high understanding related to phenomena, especially at airports with busy schedules. This study examined the causes and impacts of pilot-reported LLWS on April 5, 2018, from 13:15 to 16:00 UTC at Soekarno-Hatta International Airport which is the busiest airport in Indonesia. The data used are Doppler weather radar, automated weather observing system (AWOS), as well as synoptic and upper air observations. Based on the result of this research, linear convective clouds created from deep convection due to very unstable atmospheric circumstances are the cause of LLWS. A sizeable line of convective cloud with a 50-55 dBZ reflectivity accompanied by an outflow microburst (MBA) was detected crashing the airport. Heavy rains and strong winds up to 15-20 m/s speeds from the line of convective cloud triggered the formation of destructive LLWS. Subsequently, there was traffic build-up at 5 flight holding points before landing. Furthermore, 7 flights (Airbus, Boeing, and CRJX) underwent go-around, and 3 flights (Airbus and Boeing) were diverted.
Microbursts in the datacenter network (DCN) last for an extremely short time in switches and are difficult to discover from a coarse-grained perspective. Most prior works are dedicated to in-network ...detection of microbursts and have not yet attempted to mitigate them in real time. Therefore, a realtime microburst mitigator, called RIMM, is proposed in this work and mainly applies orderly detours with flowlet intervals for preventing packet loss and packet retransmission in the network. RIMM mainly consists of three key components: (1) detour launcher, (2) packet sequencer, and (3) post-detour handler, and can entirely work in-network on a programmable switch. Experimental results demonstrate that RIMM is capable of preventing packet loss, allowing the reduction of packet retransmissions, while effectively reducing microbursts, resulting in an enhanced data-center network performance.
Wind profiles and characteristics in a thunderstorm downburst are significantly different from that of regular boundary layer winds. This paper deals with the experimental and numerical simulation of ...a type of thunderstorm wind, namely the microburst, to study the outflow velocity characteristics. The microburst is simulated as a round jet, impinging onto a flat plate. A generic empirical equation for radial velocity profile is developed based on the experimental data, using hotwire, pressure rakes and particle image velocimetry (PIV). The experimental results are used to validate CFD simulations and to find the applicability of different turbulence models for this kind of flow. Favorable agreement between numerical and experimental studies indicates that CFD can be used for this kind of complex flow.
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