Filamentary structure in the upper atmosphere

Lead Research Organisation: University of Southampton
Department Name: Sch of Physics and Astronomy

Abstract

The subject of our study is the aurora borealis, or northern lights, which is an amazing natural lightshow in the sky, seen regularly at high latitudes such as northern Scandinavia, but rarely at the latitudes of the UK. We use the aurora as a diagnostic to find out many things about the environment around the Earth, mainly in the region of upper atmosphere called the ionosphere. That environment is made up of 'plasma' (ionised gas) often called the fourth state of matter, which makes up over 95% of the directly observable material in the cosmos. Yet it is strangely difficult to maintain and study within Earth's biosphere. The upper atmosphere provides an ideal natural laboratory for its study since there is no need to consider collisions of the plasma with container walls. The story of the aurora begins at the Sun, which is a continuous but very variable energy source, in the form of a plasma stream (the 'solar wind') which impacts on the Earth. We are interested in understanding the smallest scale auroral structures, and how the energy changes within them influence the large scale environment. To study the aurora, we use a special instrument which has three cameras looking at different 'colours' simultaneously. The proposed research is for studies of very dynamic and structured aurora at the highest possible resolution. The instrument is named ASK for Auroral Structure and Kinetics. It was designed to measure a small circle of 3 degrees in the 'magnetic zenith' i.e. straight up along the Earth's magnetic field. Particles from the Sun spiral along these imaginary magnetic field lines, and lose energy when they collide with atmospheric oxygen and nitrogen. The exact colour (or wavelength of the light) depends on how much energy the incoming particle started with, and what molecule or atom it hits. The ASK cameras help to unravel this complicated process by making very precise measurements in space and time of three emissions which have different physical origins. We will combine these optical measurements with measurements from special radar experiments, which are designed to use a technique known as interferometry to measure structures smaller than the beam width, and with accuracy of position and height better than has been possible to date. The radar imaging technology is new in the field of incoherent scattering radar and will be one of the cornerstones of a future project that is called EISCAT_3D. The technology employed is Aperture Synthesis Imaging Radar (ASIR). It is very similar to the technology used by radio astronomers (VLBI, Very Long Baseline Interferometry) to image stellar objects, and also has some similarity with the SAR (Synthetic Aperture Radar) technique used onboard airplanes and satellites to map the Earth's surface and other planetary surfaces. In the radio astronomy case the source itself spontaneously emits radiation that is collected by a number of passive antennas. In ASIR, the radar transmitter acts like a camera flash to illuminate the target (the ionosphere or atmosphere) and a number of antennas collect the scattered radiation exactly as in the radio astronomy case (or like the lens of a camera). From this point on, the two cases are essentially identical. To construct the image of the target, the cross-correlation between the signals is calculated from all different pairs of receivers. By using the radar imaging technique we will become the pioneers of this new technique in Europe.

Publications

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Whiter D (2021) Fine-scale dynamics of fragmented aurora-like emissions in Annales Geophysicae

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Dahlgren H (2011) Energy and flux variations across thin auroral arcs in Annales Geophysicae

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Lanchester B (2017) Some remaining mysteries in the aurora in Astronomy & Geophysics

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Tuttle S (2014) Calculating the auroral electron energy in Astronomy & Geophysics

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Lanchester Betty (2017) Some remaining mysteries in the aurora in ASTRONOMY & GEOPHYSICS

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Pedersen T (2010) Creation of artificial ionospheric layers using high-power HF waves in Geophysical Research Letters

 
Description 1) We have used state-of-the-art multi-wavelength imaging with radar data to quantify the energy distribution in aurora
at the highest possible temporal and spatial resolution. The optical instrument is a unique combination of three cameras which give information about the different emissions in the aurora. For example, emissions from nitrogen molecules are caused by high energy precipitation, while emissions from oxygen atoms result from low energy particles. Such emissions can be used in sophisticated models to give detailed energy distributions within narrow filaments making up the aurora. The results have been used to determine the acceleration processes responsible for several different auroral features, such as high temporal flickering, and splitting arcs.

2) We have used emissions from the long-lived oxygen ion (O+) to measure plasma flows in and around auroral arcs and to test the hypothesis that the effects of small scale structure contribute to large scale circulation. We have done this work using a new 3 dimensional model. The resulting flows are compared with large scale measurements made with radars and found to be in agreement with the direction of the flows, but with much larger magnitudes, providing evidence for the underestimates in heating (through the action of electric fields) that are made if high resolution measurements are not used.

3) We have developed the interferometry capability through international collaborations at the EISCAT Svalbard Radar to test the competing theories for the generation of naturally enhanced ion-acoustic lines (NEIAL). The technique was found to work but the number of events was small during the grant period. This work continues through our collaborators.
Exploitation Route The most direct potential relevance to UK and international research work is the application of novel radar techniques, which have been applied in the project through international collaborations, using the EISCAT Svalbard Radar and interferometry (Aperture Synthesis Interferometry). This work is ongoing and the operation of the interferometry capability will be an important diagnostic for the development stage of EISCAT-3D, Europe's next-generation radar for the study of the high-latitude atmosphere and geospace located in northern
Scandinavia.

The other main product is the application of the modelling results to high resolution observations, to provide energy and flux of the aurora at the smallest scales. The grant has leveraged support from the Citizen Science Alliance to develop an "Aurora Zoo" which will use the interested public to continue the research into auroral energy distributions in small scale structures.
Sectors Education

Environment

URL http://space.soton.ac.uk/
 
Description The aurora is a phenomenon that draws much interest from the general public and makes an excellent teaching aid about simple physical processes. Therefore under this grant we used seed funding to develop a prototype "Aurora Zoo" using summer students from Physics and Electronics and Computer Science. As a result, we took the idea forward to the Citizen Science Alliance, applying for funding to develop a full version of the Zoo for the general public. This application was successful, and led to further support in a subsequent grant, such that the Aurora Zoo is scheduled to go live in 2019.
First Year Of Impact 2012
Sector Education,Environment,Other
Impact Types Cultural

Societal

Policy & public services

 
Description Auroral Structure and Kinetics (ASK) 
Organisation Royal Institute of Technology
Department Department of Space and Plasma Physics
Country Sweden 
Sector Academic/University 
PI Contribution Shared expenses for the running of the instruments (tapes, travel, cables, optics) Shared running experiments in Svalbard, and maintaining the large data base
Collaborator Contribution Shared expenses for the running of the instruments (tapes, travel, cables, optics) Shared running experiments in Svalbard, and maintaining the large data base
Impact Award of International Fellowship between KTH and Southampton (Dr H. Dahlgren)
 
Description EISCAT Svalbard Radar Aperture Synthesis Imaging (EASI) 
Organisation Royal Institute of Technology
Department Department of Space and Plasma Physics
Country Sweden 
Sector Academic/University 
PI Contribution Radar hours awarded and shared between the three groups. Personnel sent to Svalbard to help with installation of antennas.
Collaborator Contribution Construction and supply of the interferometry antennas. Development of the software for experiment and analysis of results.
Impact PhD project (Goodbody) completing 2013
Start Year 2009
 
Description EISCAT Svalbard Radar Aperture Synthesis Imaging (EASI) 
Organisation University of Tromso
Department Department of Physics
Country Norway 
Sector Academic/University 
PI Contribution Radar hours awarded and shared between the three groups. Personnel sent to Svalbard to help with installation of antennas.
Collaborator Contribution Construction and supply of the interferometry antennas. Development of the software for experiment and analysis of results.
Impact PhD project (Goodbody) completing 2013
Start Year 2009
 
Description International Postdoctoral Award 
Organisation Royal Institute of Technology
Department Department of Space and Plasma Physics
Country Sweden 
Sector Academic/University 
PI Contribution Postdoctoral fellowship held at Southampton, but funded by Swedish Research Council. Research collaborations involve supervision and use of data from shared instruments. Postdoctoral researcher has facilities supplied for her work: space, computing support and other University amenities
Collaborator Contribution Postdoctoral fellowship held at Southampton, but funded by Swedish Research Council.
Impact Just begun.
Start Year 2013
 
Description Gave the James Dungey Lecture at the Royal Astronomical Society 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact The James Dungey Lecture is a named lecture that is open to the general public interested in Astronomy and Geophysics. The topic is chosen to give a general view of the research field, and questions are taken at the end, with the lecture being written up for publication in Astronomy and Geophysics and also reported in the Observatory. Most questions were particular to the research area, but several questions arose after the lecture from members of the public who were keen to further their knowledge.
Year(s) Of Engagement Activity 2017
 
Description Talk at Winchester Science Centre (INTECH) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? Yes
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact 170 members of public attended (and paid to attend).
Lively discussion afterwards.
Many favorable emails and feedback after the event.

Asked to return for another presentation
Year(s) Of Engagement Activity 2010
URL http://www.winchestersciencecentre.org/