Transient Atmospheric Events Research Articles

Multiscale Simulation of Offshore Wind Variability During Frontal Passage: Brief Implication on Turbines’ Wakes and Load

Enhancing the performance of offshore wind park power production requires, to a large extent, a better understanding of the interactions of wind farms and individual wind turbines with the atmospheric boundary layer over a wide range of spatiotemporal scales. In this study, we use a multiscale atmospheric model chain coupled offline with the aeroelastic Fatigue, Aerodynamics, Structures, and Turbulence (FAST) code. The multiscale model contains two different components in which the nested mesoscale Weather and Research Forecast (WRF) model is coupled offline with the Parallelized Large-eddy Simulation Model (PALM). Such a multiscale framework enables to study in detail the turbine behaviour under various atmospheric forcing conditions, particularly during transient atmospheric events.

Connections between the Transient Polar Warming and Solstitial Pause on Mars

Observations show two different transient atmospheric events around the northern winter solstice on Mars: a warming of the polar lower atmosphere (100–10 Pa) and a reduction in the near-surface wave activity. Here we examine the cause of, and connections between, these two events, and how their occurrence may have changed in past climates using a suite of Mars general circulation model simulations. These simulations show that the polar warming and pause in wave activity are connected, and they occur when there are sufficiently large dust heating rates in the southern (summer) high latitudes, which drive an expansion of the downwelling branch of the Hadley cell into the northern polar region. This causes a poleward shift and weakening of the jet, a warming of the polar lower atmosphere, and reduced baroclinic instability and waves near the surface. The occurrence and strength of the polar warming and wave activity pause increase with obliquity and dust optical depth, with a stronger dependence on obliquity. In past climates with low obliquity the warming and pause are unlikely to occur, or will be very weak, whereas during times of high obliquity they will likely be strong and occur every winter, unless the atmosphere is nearly free of dust.

Remote Sensing of the Atmosphere by the Ultraviolet Detector TUS Onboard the Lomonosov Satellite

The orbital detector TUS (Tracking Ultraviolet Setup) with high sensitivity in near-visible ultraviolet (tens of photons per time sample of 0.8 μ s of wavelengths 300–400 nm from a detector’s pixel field of view) and the microsecond-scale temporal resolution was developed by the Lomonosov-UHECR/TLE collaboration and launched into orbit on 28 April 2016. A variety of different phenomena were studied by measuring ultraviolet signals from the atmosphere: extensive air showers from ultra-high-energy cosmic rays, lightning discharges, transient atmospheric events, aurora ovals, and meteors. These events are different in their origin and in their duration and luminosity. The TUS detector had a capability to conduct measurements with different temporal resolutions (0.8 μ s, 25.6 μ s, 0.4 ms, and 6.6 ms) but the same spatial resolution of 5 km. Results of the TUS detector measurements of various atmospheric emissions are discussed and compared to data from previous experiments.

UV Transient Atmospheric Events Observed Far From Thunderstorms by the Vernov Satellite

Usually a thunderstorm region with lightning activity is necessary for the formation of known types of upper atmospheric transient luminous events (TLEs: sprites, emission of light and very low frequency perturbation, blue jets, etc.) with well-recognizable visible emissions. However, some “far-from-thunderstorm” transient events have been detected in some experiments. Measurements of transient atmospheric events (TAEs) were made on board the Vernov satellite by the sensitive UV and IR detector. Remote observation from the satellite’s orbit provided measurements all over the globe and allowed us to study events associated with thunderstorms (lightning, TLEs) and unusual UV flashes (UV TAEs) far from thunderstorm regions. More than 8500 UV TAEs were measured by the Vernov satellite over the globe. Forty seven far-from-thunderstorm TAEs were selected having no lightning discharges during 1 h in a radius of 1000 km around the location of the event according to the Worldwide Lightning Location Network (WWLLN) and Vaisala Global Lightning Data Set (GLD360) data. Special attention was given to six events with complicated temporal structure and low luminosity in the IR channel. Their properties and atmospheric conditions were studied in detail. The analysis of cloud cover in addition to the lightning location networks data demonstrated the low probability of any lightning in the region of measurements.

Transient Atmospheric Events Measured by Detectors on the Vernov Satellite

In this paper, data obtained by the Vernov satellite are discussed in comparison with the data obtained by Universitetsky–Tatiana-1, 2 satellites. The advanced instrumentation onboard the Vernov satellite improved the capabilities of the data-transmission system, providing an opportunity to acquire more detailed information on transient atmospheric events (TAEs), including a wider range of TAE photon numbers (event brightness) down to lower photon numbers, the opportunity to observe the events in ultraviolet range without the considerable inclusion of red–infrared photons (which indicates the substantial contribution of electric discharges, lightning precursors, at the altitudes of thunderstorm clouds), and the observation of TAE series at a rate of about 10–100 occurrences per second with a period from tens of seconds to several minutes.

Vernov Satellite Data of Transient Atmospheric Events

AbstractData on transient atmospheric events (TAEs) were obtained from the Vernov satellite and are presented in this paper. The data are considered in conjunction with previous data obtained by the Universitetsky-Tatiana-1 and Universitetsky-Tatiana-2 satellites. The larger volume of stored scientific data in the Vernov mission and its advanced ultraviolet (UV) and red–infrared (R–IR) radiation detector (DUV) measurements allowed improved TAE-distribution data to be obtained over a wide range of photon numbers. The difference between features of luminous transients and “dim” transients, measured by the Universitetsky-Tatiana-2 satellite, is confirmed by Vernov’s data. There are also interesting dim UV events with no R–IR radiation. Such events are expected to be deep in the atmosphere at the level of thunderstorm clouds. They might be radiated by electric discharges of less power than lightning; in fact, at the preliminary stage of lightning. The observation of repeating dim TAEs in various time intervals, starting from tens of milliseconds and up to minutes, indicates that thunderstorm electric activity is much more variable than pure lightning strikes.

RELEC mission: Relativistic electron precipitation and TLE study on-board small spacecraft

The main goal of the Vernov mission is the study of magnetospheric relativistic electron precipitation and its possible influence on the upper atmosphere as well as the observation of Transient Luminous Events (TLE) and Terrestrial Gamma Flashes (TGF) across a broad range of the electromagnetic spectrum.The RELEC (Relativistic Electrons) instrument complex onboard the Vernov spacecraft includes two identical X- and gamma-ray detectors of high temporal resolution and sensitivity (DRGE-1 and DRGE-2), three axis position detectors for high-energy electrons and protons (DRGE-3), a UV TLE imager (MTEL), a UV detector (DUV), a low frequency analyser (LFA), a radio frequency analyser (RFA), and AN electronics module responsible for control and data collection (BE).The RELEC mission conducts the following experiments:–simultaneous observations of high-energy electron and proton fluxes (within the energy range of ∼0.1–10.0MeV) and low-frequency (∼0.1–10kHz) electromagnetic wave field intensity variations with high temporal resolution (∼1ms);–fine time structure (∼1μs) measurements of transient atmospheric events in UV, X- and gamma rays with an optical imaging capability with a resolution of ∼1km in wide field of view (FOV);–measurements of electron flux pitch-angle distributions in dynamical ranges from ∼0.1 up to 105 part/cm2/s;–monitoring of charged and neutral background particles in different areas of near-Earth space.

Transient atmospheres on Charon and water–ice covered KBOs resulting from comet impacts

Evidence from stellar occultation datasets and Charon’s H2O–ice dominated surface composition has long suggested a lack of any current atmosphere around this satellite planet. However, impacts from both Kuiper Belt and Oort Cloud comets must from time to time import N2, CH4, and other cometary super-volatiles that can create temporary atmospheres around Charon. Here we estimate the frequency of such cometary impacts on Charon and the imported mass of super-volatiles from each such impact. We then examine the characteristics of such transient atmospheric events, including their column densities, mean molecular weights, scale heights, and loss timescales. We then report on the detectability of such a transient atmosphere by New Horizons, and discuss the generalized case of cometary impact-created transient atmospheres on other satellites of Pluto and water–ice covered KBOs across the Kuiper Belt.

Magnetic energy release: flares and coronal mass ejections

AbstractFree energy stored in the magnetic field is the source that powers solar and stellar activity at all temporal and spatial scales. The energy released during transient atmospheric events is contained in current-carrying magnetic fields that have emerged twisted and may be further stressed via motions in the lower atmospheric layers (i.e. loop-footpoint motions). Magnetic reconnection is thought to be the mechanism through which the stored magnetic energy is transformed into kinetic energy of accelerated particles and mass flows, and radiative energy along the whole electromagnetic spectrum. This mechanism works efficiently at scale lengths much below the spatial resolution of even the highest resolution solar instruments; however, it may imply a large-scale restructuring of the magnetic field inferred indirectly from the combined analysis of observations and models of the magnetic field topology. The aftermath of magnetic energy release includes events ranging from nanoflares, which are below our detection limit, to powerful flares, which may be accompanied by the ejection of large amounts of plasma and magnetic field (so called coronal mass ejections, CMEs), depending on the amount of total available free magnetic energy, the magnetic flux density distribution, the magnetic field configuration, etc. We describe key observational signatures of flares and CMEs on the Sun, their magnetic field topology, and discuss how the combined analysis of solar and interplanetary observations can be used to constrain the flare/CME ejection mechanism.

Atmospherically relevant ion chemistry of ozone and its cation.

The importance of ionic processes that occur in terrestrial, planetary, and stellar atmospheres is receiving increasing recognition. Actually, ions play important, often crucial, roles in a variety of atmospheric processes throughout the universe, and a strong link with the neutral chemistry is also apparent. In the terrestrial atmosphere, the ionic reactions are most relevant in those transient and fleeting events, e.g., lightning, coronas (in thunderstorm clouds and along power lines), where the local ion density is much higher than in unperturbed air, and the chemical systems are typically far from equilibrium. In such cases, ozone, a key molecule for the terrestrial atmosphere, is also present in high local concentrations; it is formed from O(2) by the same transient event. Accordingly, this review provides a survey of the positive ion chemistry of ozone with several of the most important "atmospheric" species: the reactions, the products, and the importance of the examined processes are discussed also in the light of the local thermodynamic disequilibrium (LTD) approach to the chemistry of transient atmospheric events. In all such studies, mass spectrometry is traditionally, and remains today, the experimental technique of choice. The novel application of mass spectrometry to the study of neutral species (NRMS), highly successful for the preparation and positive detection of long-sought, otherwise inaccessible, short-lived neutrals, makes mass spectrometry the most powerful tool now available for the study of the species and processes that are relevant to atmospheric chemistry. Selected examples of the interlink between the neutral and the ionic chemistry are also illustrated.

Sulfur Dioxide in the Atmosphere of Venus: I. Sounding Rocket Observations

In this paper we present ultraviolet reflectance spectra obtained during two sounding rocket observations of Venus made during September 1988 and March 1991. We describe the sensitivity of the derived reflectance to instrument calibration and show that significant artifacts can appear in the spectrum as a result of using separate instruments to observe both the planetary radiance and the solar irradiance. We show that surfur dioxide is the primary special absorber in the 190-230 nm region and that the range of altitudes probed by these wavelengths is very sensitive to incidence and emission angles. In a following paper Na et al. (1994, Icarus 112, 389-395) show that sulfur monoxide features are also present in these data. Accurate identification and measurement of additional species require observations in which both the planetary radiance and the solar irradiance are measured with the same instrument. The instrument used for these observations is uniquely suited for obtaining large phase angle coverage and for studying transient atmospheric events on Venus because it can observe targets within 18° of the Sun while Earth-orbiting instruments are restricted to solar elongation angles ≥ 45°.

Possible forcing effects of net evaporation, atmospheric pressure, and transients on water transports in the Mediterranean Sea

The present paper examines the influence of evaporation fluxes over the Mediterranean Sea on water flows through the straits of Gibraltar and Sicily. Evaporation fluxes are estimated from European Centre for Medium‐Range Weather Forecasts atmospheric analyzed fields for the period 1981–1985. An aerological approach is followed to evaluate the net water exchanged between the sea and the atmosphere. The resulting Mediterranean Sea circulation is then deduced from water budget in the sea. Net evaporation is found to be the major forcing for the circulation through the straits. Mean flows through the Strait of Gibraltar are found to be slightly weaker than commonly accepted values but appear to be close to recent estimations. Temporal variations of net evaporation show a relatively important annual cycle which may induce significant annual cycle of water flows through the straits. For each month of the studied period, fluxes are separated into two parts: a steady state flux and transients. Transient atmospheric events generate a net water loss in the Mediterranean and may induce a net water inflow through Gibraltar. The latter flow is suggested to be related to Atlantic/Mediterranean water interface fluctuations. Water sinking is also investigated. It is mainly related to the mean component of atmospheric events in the eastern Mediterranean and to transient events in the western Mediterranean. Atmospheric pressure effect shows a significant variability, especially during winter, and may induce a slight water flow through the straits.