TEA-IS
Thunderstorm Effects on the Atmosphere-Ionosphere System (TEA-IS) is a recentlty approved ESF Research Networking Programme which started in May 2011 and will last until May 2016. So far there are more than 100 scientists from nine countries involved.
For further information, read below:
- Introduction
- Status of the relevant research field; Scientific context
- Objectives
- Achievements
- Facilities and expertise which would be accessible by the Programme
Thunderstorm effects on the atmosphere-ionosphere system
Two surprising phenomena have been observed above thunderstorms in the last twenty years; these are huge electric discharges in the stratosphere and mesosphere, and energetic bursts of gamma-radiation observed from satellites. Their late discovery demonstrates that our understanding of thunderstorms and of processes in the atmosphere above them is limited. They further underscore the point that thunderstorms affect not only the troposphere but all atmospheric layers and nearEarth space, and that several research fields must combine to advance our knowledge of the effects of thunderstorms on the atmosphere-ionosphere system.
Two European space missions are planned for studies of thunderstorms and atmospheric coupling. They are the Atmosphere-Space Interactions Monitor (ASIM) of the European Space Agency (ESA) and the French satellite “Tool for the Analysis of RAdiations from lightNIngs and Sprites” (TARANIS) developed by the French space agency Centre National d'Etudes Spatiales (CNES). To be both launched in 2018, the missions will study electric discharges above thunderstorms, thunderstormgenerated atmospheric gravity waves, and thunderstorm cloud properties.
Preparatory activities include deployment of new ground instrumentation for observing thunderstorms, planning of balloon-campaigns to study the atmosphere above thunderstorms, laboratory experiments, and development of theory and models. These activities will provide an essential context for the satellite measurements. This networking programme will help to coordinate the activities, and to structure and expand the European research community behind the missions towards the common goal of studying fundamental thunderstorm processes and their impacts. This task requires a multi-disciplinary approach of geosciences and physics, and of observations, experiments and theory. The applications are as diverse as the science, ranging from the industrial use of electric discharges to improved understanding of the role of thunderstorms in a changing climate. The programme will stimulate the exchange of methods and results between the European and international communities involved.
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Status of the relevant research field; Scientific context
The courageous lightning experiments of Benjamin Franklin and Jacques de Romas in the 18th century led to discoveries of fundamental aspects of electricity; they began our journey of exploration into gas discharge phenomena. After many years of research the very process of lightning initiation is still debated, and surprises are still in store.
Consider the chance discovery in 1989 of flashes in the mesosphere at 50−80 km altitude above thunderstorms, now known as “sprites”. Although electrical breakdown between thunderclouds and the ionosphere was discussed by the Nobel laureate C. T. R. Wilson in 1925, its discovery came as a surprise to scientists. Consider another serendipitous discovery a few years later, in 1994, of sub-millisecond duration bursts of –rays from the atmosphere above thunderstorms with energies exceeding 300 keV. These Terrestrial Gamma-Ray Flashes (TGFs) were observed by detectors on the Compton Gamma Ray Observatory (CGRO) satellite designed to observe such radiation from space. The discovery of new phenomena above thunderstorms was topped in 2002 with observations of the longest electric discharge on planet Earth, a gigantic jet reaching from thunderstorm clouds - through the stratosphere and mesosphere - to the bottom of the ionosphere, at 90 km altitude. These discoveries have given extra momentum to research in atmospheric electricity and, more generally, on how thunderstorms interact with the atmosphere and ionosphere.
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The physics of atmospheric electricity
It is generally accepted that noninductive collisions between graupel and smaller ice crystals, in the presence of liquid water, represent an efficient charging mechanism of thunderstorm clouds and that the combination of this microphysical process and of large-scale cloud dynamics lead to electric dipole and/or tripole structures in clouds. The ambient electric field measured from instrumented balloons may reach more than 100 kV/m; however, this is not enough to cause electrical breakdown. Mechanisms for lightning triggering that have been suggested include relativistic electrons created by cosmic rays or local electric field enhancements produced by hydrometeors. Alternatively, the relatively few in situ observations may not have captured the maximum electric field.
The sprite discharge is driven by the quasi-electrostatic (QE) field in the mesosphere following a positive cloud-to-ground (+CG) flash in a thundercloud below, jets are formed by space charge fields at cloud tops and elves are the signature of heating of the atmosphere at the lower ionosphere by the lightning electromagnetic pulse. Together these phenomena are known as Transient Luminous Events (TLEs). As with lightning, the triggers of sprites and jets are under discussion (e.g. cosmic rays, meteors, gravity waves). The processes of TGF generation are also under intense investigation, but still remain unknown. The discoveries of TLEs and TGFs have increased our understanding of the electric discharge. TGFs have pointed to the importance of high-energy electron production, which is now known also to be common in tropospheric lightning. Because the discharge time-scales of sprites are longer in the tenuous mesosphere, imaging instruments with high frame rates can resolve the dynamics of streamer formation and propagation, so providing new information on the basic physics of the gas discharge.
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Lightning field-induced perturbations to the atmosphere-ionosphere
Lightning couples energy directly to the mesosphere and lower ionosphere through quasi-electrostatic (QE) and electromagnetic pulsed (EMP) fields. The fields heat the partly ionised atmosphere and cause additional ionisation, thereby changing the atmospheric conductivity. Electromagnetic waves from lightning discharges may also have an indirect effect on the lower ionosphere via reflection effects or interactions with radiation belt electrons that can be precipitated from the magnetosphere into the upper atmosphere. Perturbations to the ionosphere are observed as perturbations to the amplitude and/or phase of signals from Very Low Frequency (VLF) transmitters used for submarine communications. Quantitative estimates of ionisation and heating by TLEs are still lacking but can in principle be modelled. They hold the promise of new insights into the properties and microphysics of the mesosphere.
Chemical perturbations include the production of nitric oxide (NO) by lightning. It is of the order of 5 Tg N/year, corresponding to 10% of the total emissions today and 40% of the pre-industrial emissions. However, in the upper troposphere, lightning is the major source of NOx. NO in the troposphere is important because it modifies the ozone (O3) and methane (CH4) chemistry, increasing the concentration of the former and reducing that of the latter. Some important challenges remain, such as improving the quantification of NO production by lightning and understanding better the roles of lightning in global change. Likewise, the local effects of TLEs on upper atmospheric chemistry are not well understood. Better observations and kinetic models of the electric discharge are needed to answer these and other important questions.
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Convection-induced perturbations to the atmosphere-ionosphere
Thunderstorms in the tropics are powerful fountains that pump trace gases from the lower to the upper troposphere and into the stratosphere where they may reside for several months. Water vapour is one of the most effective greenhouse gases in the atmosphere, and understanding its transport in the atmosphere is crucial for understanding climatic variability. However, the non-uniform mixing of water vapour, and changes between ice, water and water vapour, make its behaviour much harder to understand than that of carbon dioxide. Some important processes in the hydrological cycle, such as the formation of cloud condensation nuclei and cirrus clouds in the lower stratosphere, are not well understood. With global warming at the Earth?s surface, tropical deep cumulus convection is expected to become even more powerful and frequent, and global troposphere/stratospheric water vapour transport enhanced, leading to further heating of the atmosphere on a global scale.
Gravity waves in the mesosphere produced by thunderstorms are observed in the hydroxyl (OH) nightglow layer by ground-based cameras and by microbarometer networks. Observations in the different atmospheric night-glow layers are needed to determine the penetration of such waves into the upper atmosphere and to assess their impact on the global stratospheric and mesospheric circulation. It is known that forcing by wave activity in the stratosphere contributes to the upward and poleward large scale circulation in the stratosphere and mesosphere. However, observations are still rare, and our present understanding of their effect on the upper atmosphere is limited.
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Objectives
The objectives of this network are to understand the role of thunderstorms in the atmosphere-ionosphere-magnetosphere system and also anthropogenic influences on thunderstorms. The holistic approach adopted here leads us to study a multitude of 4 processes and their interdependencies; some processes are of such a fundamental nature that the insights gained are expected to have impacts even beyond the field of atmospheric science. The scientific topics to be studied are summarized as follows:
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The physics of atmospheric electricity
- Fundamentals of thundercloud formation and electrification
- Fundamentals of atmospheric electric discharges
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Lightning field-induced perturbations to the atmosphere-ionosphere
- Ionisation and conductivity perturbations, and their larger scale effects
- Perturbations to atmospheric chemical composition
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Convection-induced perturbations to the atmosphere-ionosphere
- The upper-troposphere/lower stratosphere interface
- Gravity wave perturbations to the stratosphere, mesosphere, ionosphere
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Applications
- Technological plasma systems
- The Earth?s atmosphere, weather, climate and climate change
The programme will help to prepare the European and international research community for the ASIM and TARANIS missions (see www.electricstorms.net). Planned for launch in 2018, the missions will study electric discharges above thunderstorms, atmospheric gravity waves and thunderstorm cloud properties. The missions are the first simultaneously to observe lightning, TLEs and TGFs with dedicated instruments, thus allowing studies of their inter-relationships. Preparations already underway include the fielding of new instrumentation for observing thunderstorms and TLEs from the ground or balloons, laboratory experiments on
electric discharges, and developing improved models of the electric discharge and various effects in the atmosphere.
The planned activities provide an excellent and essential context for the satellite measurements which would not be of nearly the same value unless the wider context is considered and better understanding obtained. The network will permit objectives that are not directly studied by the space missions, such as the effects of thunderstorms on atmospheric circulation and their role in a changing climate, to be added.
The programme proposed here will be based on these activities and help with their coordination. It will structure the European research community to take full advantage of the space mission data when they become available. Even if either mission is later postponed or fails on launch, this programme will generate a wide range of important and fascinating results.
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Achievements
Areas within research and applications where we foresee significant advances are:
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Physics of atmospheric electricity
- Dust and aerosol effects on cloud formation and electric charging
- Initiation of discharges
- Generation of high-energy radiation and its effects on streamer dynamics
- Lightning detection and protection techniques
- Technical applications of plasma discharges
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Lightning field-induced perturbations to the atmosphere-ionosphere
- Ionisation and heating of the atmosphere caused by TLEs
- Chemical perturbations by lightning and TLEs
- Propagation of electromagnetic fields in complex plasmas
- Instabilities and scintillations in the ionosphere, and their effects on GNSS (Galileo and GPS) signal quality5
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Convection-induced perturbations to the atmosphere-ionosphere
- Transport of water vapour and trace gases in thunderstorms
- Influence of gravity waves on the dynamics of the upper atmosphere and ionosphere and their influence on the dynamics of these regions
- Characterisation of trace gas circulation in climate models
- Role of thunderstorms in the Earth?s changing climate
Many of these topics are interrelated. It is the task of the networking programme to facilitate the interactions between the topic areas, to pull all the results together, and to develop improved models, for the proper advancement of both science and technology.
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Facilities and expertise which would be accessible by the Programme
The programme partners representing most of the research areas are amongst the leaders of their fields; a particular effort will be made to attract scientists in areas that need strengthening. Some of the facilities available (see also www.electricstorms.net) include:
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ASIM and TARANIS
- X- and -rays, optical, plasma and EM waves
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Optical ground-based observations of lightning, TLEs and Meteors
- TV frame-rate imaging (France, Spain, Italy, Poland, Hungary, Israel)
- High frame-rate imagers (10 kHz) with spectrometer option (0.03nm) (Spain)
- Differential Optical Absorption Spectroscopy for monitoring the NO2 and O3(Italy, Bulgaria)
- Dedicated meteor detection networks (several countries)
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Lightning detection networks
- Profeus, EUCLID and LINET
- Schumann resonance stations (Hungary, Israel)
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Instrumented towers
- The Gaisberg (Austria) and Santis (Switzerland) instrumented radio towers for correlated lightning current and field measurements
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Ground-based VLF navigational transmitter-receiver radio network
- Receivers at universities in Morocco, Algeria, Tunis, Libya, Egypt, Greece, Turkey in the AWESOME network funded by the UN via Stanford University
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Numerical models
- Kinetic and hybrid codes of electric discharges and their chemical perturbations
- Coupling of thunderstorm radiation to the atmosphere-ionosphere (France)
- Cloud microphysics and dynamics (Italy).
- Electromagnetic radiation from lightning (Sweden).
- Chemistry-ionosphere-climate model (UK and Switzerland).
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Balloon investigations
- Campaigns planned for South America to observe thunderstorm processes from 2012.
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Other research Satellites
- MIPAS/ENVISAT and SABER/TIMED measurements for studies of TLE perturbations to atmospheric composition.
- COSMIC GPS occultation data for observation of water vapour above thunderstorms
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Laboratory facilities
- Discharges and hard X-ray emissions by long sparks (Eindhoven University of Technology)
- Graupel charging (University of Manchester)
- DC and corona discharges/optical spectroscopy (Institute of Plasma Physics, Czech Republic)
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