An optical flash on Venus detected by the AKATSUKI spacecraft

Icarus, 1985

Laser-induced plasmas in various gas mixtures were used to simulate lightning in other planetary atmospheres. This method of simulation has the advantage of producing short-duration, high-temperature plasmas free from electrode contamination. The laser-induced plasma discharges in air are shown to accurately simulate terrestrial lightning and can be expected to simulate lightning spectra in other planetary atmospheres. Spectra from 240 to 880 nm are presented for simulated lightning in the atmospheres of Venus, earth, Jupiter, and Titan. The spectra of lightning on the other giant planets are expected to be similar to that of Jupiter because the atmospheres of these planets are composed mainly of hydrogen and helium. The spectra of Venus and Titan show substantial amounts of radiation due to the presence of carbon atoms and ions and show CN Violet radiation. Although small amounts of CH4 and NH3 are present in the Jovian atmosphere, only emission from hydrogen and helium is observed. Most differences in the spectra can be understood in terms of the elemental ratios of the gas mixtures. Consequently, observations of the spectra of lightning on other planets should provide in situ estimates of the atmospheric and aerosol composition in the cloud layers in which lightning is occurring. In particular, the detection of inert gases such as helium should be possible and the relative abundance of these gases compared to major constituents might be determined.

Icarus, 2021

Sources and characteristics of light-absorbing fine particulates over Delhi through the synergy of real-time optical and chemical measurements

Journal of Geophysical Research: Atmospheres, 2001

We present long optical and radio frequency (RF) time series of lightning events observed with the FORTE satellite in January 2000. Each record contains multiple RF and optical impulses. We use the RF signatures to identify the general type of discharge for each impulse according to the discrimination techniques described by and reviewed herein. We see a large number of paired, impulsive events in the RF which allow us to study the heights within clouds of several events. We also see that the rate of RF/optical coincidence depends on the type of discharge: nearly 100% of VHF signals from first negative return strokes have an associated optical signal, whereas a mere 50% of impulsive intracloud events appear to have an optical counterpart. While the RF signals from ground strokes clearly coincide with simple optical signals in almost all cases, the intracloud lightning often shows nearly continuous, complicated RF and optical emissions which do not cleanly correlate with one another. The RF and optical pulses do not show a well-defined relationship of intensities, for any lightning type. The observed delay between the RF and optical pulses we interpret as mainly an effect of the scattering experienced by the light as it traverses the cloud. For intracloud lightning, we find no evidence of an intrinsic delay at the source between the onset of the RF and optical signals. Impulsive in-cloud RF events are seen to occur on average every 0.9 ms during a flash. This paper is not subject to U.S.

Journal of Geophysical Research, 2000

Preliminary observations of simultaneous VHF and optical emissions from lightning as seen by the Fast on-Orbit Recording of Transient Events (FORTE) spacecraft are presented. VHF/optical waveform pairs are routinely collected both as individual lightning events and as sequences of events associated with cloud-to-ground (CG) and intracloud (IC) flashes. CG pulses can be distinguished from IC pulses on the basis of the properties of the VHF and optical waveforms but mostly on the basis of the associated VHF spectrograms. The VHF spectrograms are very similar to previous ground-based HF and VHF observations of lightning and show signatures associated with return strokes, stepped and dart leaders, attachment processes, and intracloud activity. For a typical IC flash, the FORTE-detected VHF is generally characterized by impulsive broadband bursts of emission, and the associated optical emissions are often highly structured. For a typical initial return stroke, the FORTE-detected VHF is generated by the stepped leader, the attachment process, and the actual return stroke. For a typical subsequent return stroke, the FORTE-detected VHF is mainly generated by dart leader processes. The detected optical signal in both return stroke cases is primarily produced by the in-cloud portion of the discharge and lags the arrival of the corresponding VHF emissions at the satellite by a mean value of 243 s. This delay is composed of a transit time delay (mean of 105 s) as the return stroke current propagates from the attachment point up into the region of in-cloud activity plus an additional delay due to the scattering of light during its traversal through the clouds. The broadening of the light pulse during its propagation through the clouds is measured and used to infer a mean of this scattering delay of about 138 s (41 km additional path length) for CG light. This value for the mean scattering delay is consistent with the Thomason and Krider [1982] model for light propagation through clouds.

Journal of Geophysical Research, 2003

1] The Optical Transient Detector (OTD) is a space-based instrument specifically designed to detect and locate lightning discharges as it orbits the Earth. This instrument is a scientific payload on the MicroLab-1 satellite that was launched into a 70°inclination low Earth orbit in April 1995. Given the orbital trajectory of the satellite, most regions of the Earth are observed by the OTD instrument more than 400 times during a 1 year period, and the average duration of each observation is 2 min. The OTD instrument optically detects lightning flashes that occur within its 1300 Â 1300 km 2 field of view during both day and night conditions. A statistical examination of OTD lightning data reveals that nearly 1.4 billion flashes occur annually over the entire Earth. This annual flash count translates to an average of 44 ± 5 lightning flashes (intracloud and cloud-to-ground combined) occurring around the globe every second, which is well below the traditional estimate of 100 fl s À1 that was derived in 1925 from world thunder day records. The range of uncertainty for the OTD global totals represents primarily the uncertainty (and variability) in the flash detection efficiency of the instrument. The OTD measurements have been used to construct lightning climatology maps that demonstrate the geographical and seasonal distribution of lightning activity for the globe. An analysis of this annual lightning distribution confirms that lightning occurs mainly over land areas, with an average land/ocean ratio of $10:1. The Congo basin, which stands out year-round, shows a peak mean annual flash density of 80 fl km À2 yr À1 in Rwanda, and includes an area of over 3 million km 2 exhibiting flash densities greater than 30 fl km À2 yr À1 (the flash density of central Florida). Lightning is predominant in the northern Atlantic and western Pacific Ocean basins year-round where instability is produced from cold air passing over warm ocean water. Lightning is less frequent in the eastern tropical Pacific and Indian Ocean basins where the air mass is warmer. A dominant Northern Hemisphere summer peak occurs in the annual cycle, and evidence is found for a tropically driven semiannual cycle.

Icarus, 1983

The possibililies of lightning generation on other planets are considered, and the basic conditions that exist in terrestrial clouds during lightning discharges and the various theories of charge separation are reviewed. Recent measuremenls of cloud structure and whistlers, as well ,is oplical observation of lightning on Jupiter. suggest lhal charge separation and lightning discharges occur on other planets in ways similar to those in which lhe} occur on Earth. Using these terrestrial ideas, it is concluded that lightning on Venus will probably bc foumt in clouds that are located in regions of convection such as those observed downwind of the subso[ar point. It is also possible thal if volcanoes on Venus are erupting, the}' too can produce lightning discharges in their plumes althotlgh it seems unlikely lhal lhis process can account for the observed rate of discharge. Jovian lightning is most probably generated in the lower water-ice clouds. These clouds are of moderate temperatures and have strong convection and large mass loading, all important ingredients for electrical buildup, l,ightning is all bill ruled out for Mars. even though some electrilication ix possible owing to the large dusl Molms on that planel.

2009

This article provides a brief survey of the space-and ground-based studies of lightning performed by investigators at Los Alamos National Laboratory (LANL). The primary goal of these studies was to further understand unique lightning signatures known as Narrow Bipolar Events (NBEs). First, an overview is presented of the Fast On-orbit Recording of Transient Events (FORTE) satellite and of the ground-based Los Alamos Sferic Array (LASA). This is followed by a summary of the phenomenology, physics, and meteorological context of NBEs and NBE-related discharges. This article also discusses additional radio frequency and optical observations of lightning made by the FORTE satellite and concludes with an outlook on LANL's growing interest in the use of lightning observations in the study of severe weather and hurricane intensification.

Remote Sensing

We present spectroscopic diagnostic methods that allow us to estimate the gas and the electron temperature in emerged lightning stroke channels (from thunderclouds) observed by the photometers and cameras of the Atmosphere Space Interaction Monitor (ASIM). We identify the species (molecules, atoms and ions) producing light emission in different wavelengths, and how the blue (337 ± 2 nm), red (777.4 ± 2.5 nm) and ultraviolet (180–230 nm) optical emissions captured by ASIM photometers change as a function of the temperature in the lightning stroke channel. We find good agreement between the light curves of the emerged lightning observed by ASIM and the synthetic ones obtained from calculated spectra. Our results suggest that (i) early stage (high temperature > 20,000 K) emerged lightning strokes at high altitude can contribute to the optical signals measured by the PH2 photometer (180–230 nm), (ii) intermediate stage (mid temperatures, 6000–21,000 K) emerged lightning strokes can p...

We present the latest observations from spacecraft and ground-based instruments in search for lightning activity in the atmospheres of planets in the solar system, and put them in context of previous research. Since the comprehensive book on planetary atmospheric electricity compiled by Leblanc et al. (2008), advances in remote sensing technology and telescopic optics enable detection of additional and new electromagnetic and optical emissions, respectively. Orbiting spacecraft such as Mars Express, Venus Express and Cassini yield new results, and we highlight the giant storm on Saturn of 2010/2011 that was probably the single most powerful thunderstorm ever observed in the solar system. We also describe theoretical models, laboratory spark experiments simulating conditions in planetary mixtures and map open issues.

Icarus

Measurements of the spectral irradiance from approximately 380 to 820 nm are reported for laboratory simulations of lightning in the atmospheres of Venus, Jupiter, and Titan. The observations were made at 1 and 5 bars of pressure for Venus and Jupiter and at 1 bar for the Titan mixture. The spectra were obtained by observing laser-induced plasmas with a scanning spectrometer and an optical multichannel analyzer. Simulations of lightning show that atomic line and continuum radiation dominate the spectra. Weak molecular band radiation from CN was also observed for Venus and Titan. As the ambient pressure was increased from 1 to 5 bars, the prominence of the line radiation diminishes compared to the continuum radiation, some lines disappear, and the intensity of the molecular band radiation increases. Laboratory results for the venusian lightning spectrum are consistent with those found by the Venera 9 spectrometer when it viewed a storm on the nightside of Venus. For both Jupiter and ...