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New insights to the north-south asymmetries of auroral features

New insights to the north-south asymmetries of auroral features

Recent research on the simultaneous displays of aurora in both hemispheres have lead to new knowledge of how large-scale asymmetries in the global magnetic field configuration can arise and be mitigated. This new understanding is contrary to what has been the consensus in the field, and was recently highlighted in a press release from the American Geophysical Union, followed by attention from numerous newspapers and magazines world wide.

These new results, published in a series of papers since 2015 [1,2,3,4,5,6], represents a paradigm shift in the explanation of the processes controlling how the magnetosphere twists around the Sun-Earth line. It has been known since the 1980’s that when the Interplanetary Magnetic Field (IMF) has a dawn-dusk component (By), the closed field lines inside the magnetosphere also develop a By in the same direction as the IMF. This has usually been explained by means of tail reconnection, a process that would allow field lines from each hemisphere to meet and produce new closed field lines, now being asymmetric. However, the new results show that the asymmetry of closed field lines, as highlighted by the aurora in one hemisphere being longitudinally displaced to its counterpart in the opposite hemisphere, start to emerge within 10 minutes. This is a much shorter response time than what can be explained by the the tail reconnection scenario. Furthermore, the highlighted studies also show that the process of tail reconnection actually act to reduce the longitudinal displacement of the northern and southern aurora. This is exactly opposite to the understanding that has been the consensus in the community, hence the importance of these results. In the AGU press release, editor-in-chief of JGR-Space Physics, Mike Liemohn, says: “This study explains both how asymmetries are created and how it is removed and it is exactly opposite of what I and many researchers have thought. Therefore, this result is kind of big deal.”

Director of the Birkeland Centre for Space Science and leader for the research group presenting the new findings, Nikolai Østgaard, says: “We are very satisfied with how the AGU Press Release turned out for us. As we speak, 104 newspapers and magazines worldwide has picked up the story. We could not have hoped for a wider impact among the public about our results.”

Along with the press release, the research group at the Birkeland Centre for Space Science  prepared an animation of the processes leading to the longitudinal displacement of the aurora between the two hemispheres. This can be seen in the video below.

 

A more in-depth explanation of the mechanism can be seen in the video below where PhD candidate Anders Ohma, lead author of the JGR paper highlighted in the AGU press release, explains the physics behind the longitudinal displacement of the aurora between the two hemispheres.

 

 

[1] Tenfjord, P., Østgaard, N., Snekvik, K., Laundal, K. M., Reistad, J. P., Haaland, S., & Milan, S. E. (2015). How the IMF By induces a By component in the closed magnetosphere and how it leads to asymmetric currents and convection patterns in the two hemispheres. Journal of Geophysical Research: Space Physics, 120. https://doi.org/10.1002/2015JA021579

[2] Reistad, J. P., Østgaard, N., Tenfjord, P., Laundal, K. M., Snekvik, K., Haaland, S., … Grocott, A. (2016). Dynamic effects of restoring footpoint symmetry on closed magnetic field-lines. Journal of Geophysical Research: Space Physics, 121, 1–14. https://doi.org/10.1002/2015JA022058

[3] Tenfjord, P., Østgaard, N., Strangeway, R., Haaland, S., Snekvik, K., Laundal, K. M., … Milan, S. E. (2017). Magnetospheric response and reconfiguration times following IMF By reversals. Journal of Geophysical Research: Space Physics, 122(1), 417–431. https://doi.org/10.1002/2016JA023018

[4] Reistad, J. P., Østgaard, N., Laundal, K. M., Ohma, A., Snekvik, K., Tenfjord, P., … Haaland, S. E. (2018). Observations of asymmetries in ionospheric return flow during different levels of geomagnetic activity. Journal of Geophysical Research: Space Physics. https://doi.org/10.1029/2017JA025051

[5] Østgaard, N., Reistad, J. P., Tenfjord, P., Laundal, K. M., Rexer, T., Haaland, S. E., … Ohma, A. (2018). The asymmetric geospace as displayed during the geomagnetic storm on 17 August 2001. Annales Geophysicae, 36, 1577–1596. https://doi.org/10.5194/angeo-36-1577-2018

[6] Ohma, A., Østgaard, N., Reistad, J. P., Tenfjord, P., Laundal, K. M., Snekvik, K., … Fillingim, M. O. (2018). Evolution of Asymmetrically Displaced Footpoints During Substorms. Journal of Geophysical Research: Space Physics, 123. https://doi.org/10.1029/2018JA025869

Web-based Tools for Forecasting Solar Particle Events and Flares

Web-based Tools for Forecasting Solar Particle Events and Flares

The presence of Solar Energetic Particles (SEPs) poses a serious health risk to humans in space, can result in increased radiation doses for high-latitude aircraft flights and constitutes a serious hazard for the micro-electronics and other hardware elements of satellites, aircraft and launchers. These groups of end users need reliable forecasts of possible enhancements in the radiation flux level, days beforehand, in order to plan flights, operations and EVAs (extra-vehicular activities).

Enhancements of SEP fluxes result from explosive phenomena in the solar corona; these enhancements are known as Solar Particle Events (SPEs). There are two phenomena known to contribute to SPEs namely, Solar Flares and Coronal Mass Ejections. CME-driven shocks might be the key driver but Solar Flare forecasting is much more advanced and SPEs driven by shocks normally have associated flares.

The last five years the Space Research and Technology Group of the Institute for Astronomy, Astrophysics, Space Applications & Remote Sensing (IAASARS), of the National Observatory of Athens (NOA), has been involved in the development of new techniques and in the operation of web based tools, to provide reliable Solar Particle Events and Flares predictions.

The FORSPEF Tool

The FORSPEF (FORecasting Solar Particle Events and Flares) tool was developed with funding from ESA’s Technology Research Programme (ESA Contract No. 4000109641/13/NL/AK).  In Figure 1 a summary of the operation capabilities of the FORSPEF tool is presented (for more details see Anastasiadis et al., 2017).

Figure 1: A summary of the operational capabilities of the FORSPEF Tool

 

The FORSPEF tool is a prototype system that consists of three modules that aim to forecast i) the likelihood of upcoming solar flare eruptions, ii) the occurrence of Solar Energetic Particle (SEP) events by making a prediction of the time before onset, and iii) the SEP characteristics for an upcoming event, respectively. Additionally, FORSPEF incorporates two operational modes, the forecasting and the nowcasting mode. The former is understood as the pre-event mode, since no actual solar event (i.e. SF or CME) has yet taken place. The only available information is the identification of an AR on the Sun and its calculated Beff metric (see Georgoulis and Rust 2007). The latter corresponds to the post-event mode, in which a solar event has actually taken place and its characteristics (for solar flares the longitude and the magnitude, and for CMEs the width and the velocity) are available.

The solar flare forecasting module delivers conditional flare probabilities complemented by information on CME probabilities and expected CME speeds. The prediction of SFs relies on the effective connected magnetic field strength (Beff) metric, which is based on an assessment of potentially flaring AR magnetic configurations, and it uses a sophisticated statistical analysis of a large number of AR magnetograms. CME probabilities and projected speeds are based on the peer-reviewed published flare-to-CME association rates (Yashiro et al., 2005) and on the statistical correlation between Beff-values and recorded near-Sun CME velocities (Georgoulis, 2008), respectively. For each identified solar AR, the output of the FORSPEF flare forecasting module is a structure containing the AR NOAA number, its location, the corresponding Beff value, the 24-hour cumulative flare probabilities for each of the 28 GOES flare classes (from C1.0 to X10.0) and their peak photon fluxes (PPFs), the respective eruptive-flare or CME likelihoods, and the projected CME velocity. The SF forecasting produces histogram curves of the cumulative flare probabilities and CME likelihoods versus the flare PPF. The cumulative forecast probabilities for flares and CME likelihood for a sample AR are shown in Figure 2.

Figure 2: Pictorial output of the FORSPEF solar flare forecasting and likelihood of CME

For the prediction of SEP events, new statistical methods have been developed. These are based on a comprehensive database of SFs, CMEs and SEP events (Papaioannou et al., 2016). In the forecasting scheme, the FORSPEF tool provides the probability of SEP occurrence based on the information delivered by the solar flare forecasting. The kernel of the SEP prediction is based on the probability of SEP occurrence per solar flare magnitude which is derived from a historical sample of 4000 flares. These probability values are used to implement a local SEP statistical model via distribution functions. The FORSPEF tool in this forecasting scheme provides a weighted forecast for the expected occurrence of an SEP event per AR, calculated as the product of the local SEP module and the cumulative SF probabilities. The output of the SEP forecasting scheme is the maximum probability for each of the considered ARs (Papaioannou et al., 2015; Anastasiadis et al., 2017).

Figure 3: Pictorial output of the FORSPEF of the probability of SEP occurrence as a function of Solar flare flux and longitude

FORSPEF’s nowcasting scheme can be considered as the short-term forecasting that is triggered by a solar eruptive even. FORSPEF has developed two operational nowcasting modules –one that is based on near real-time solar flare information (longitude, magnitude) and another module that makes use of near-real time coronal mass ejection – CME data (width, velocity). For the first operational module the inputs of the FORSPEF nowcasting work-scheme are in practice the maximum flare flux and its position (longitude) on the visible part of the solar disk. FORSPEF makes use of all ≥C1.0 flares. For the second operational module the nowcasting scheme uses the near real-time outputs provided online through the computer-aided CME tracking software (CACtus), operated by ROB. Further details on this module are presented in the recent work of Papaioannou et al. (2018).

The FORSPEF tool has been released on April 06, 2015 and has been in continuous operation ever since. The FORSPEF system is registered to the SEP Scoreboard Challenge of the Community Coordinated Modeling Center (CCMC) of NASA. It is available online at http://tromos.space.noa.gr/forspef/ and provides continuous forecasts and nowcasts of SFs and SEP events. All outputs can be freely accessed and used by the scientific community.

The ASPECS activity

The ASPECS (Advanced Solar Particle Event Casting System) tool is currently under development by a consortium headed by the Space Research and Technology Group of the IAASARS/NOA, with funding through the ESA Contract No 4000120480/17/NL/LF/hh “Solar Energetic Particle (SEP) Advanced Warning System (SAWS)”. The consortium consists of an SME, SPARC (Greece); the University of Turku (Finland); the Universitat de Barcelona (UdB) and the Belgian Institute for Space Aeronomy (BIRA-IASB).

Figure 4: The ASPECS logo

ASPECS will collate and combine outputs from different modules providing forecasts of solar phenomena, solar proton event occurrence and solar proton flux and duration characteristics; tailored to the needs of different spacecraft and launch operators, as well as the aviation sector. The predictions shall start with the solar flare forecasting and will continuously evolve through updates based on near-real time inputs (e.g. solar flare and coronal mass ejections data/characteristics) received by the system. User requirements include a derivation of energies and thresholds important for different user-groups and warning levels. In addition, for the first time the complete time profile of the SEP event at respective energies shall be provided in near real-time, utilizing both simulations and observations.  More info and updates on the current activity can be found at http://tromos.space.noa.gr/aspecs.

 

This post is written by:

Dr. Anastasios Anastasiadis

Research Director

National Observatory of Athens

Institute for Astronomy, Astrophysics, Space Applications & Remote Sensing

A close-up journey to the Sun: The Parker Solar Probe Mission

A close-up journey to the Sun: The Parker Solar Probe Mission

Almost two months ago, in August 12, 2018 Parker Solar Probe (PSP) launched by NASA on a Delta IV Heavy rocket from Cape Canaveral, Florida. This is a long-awaited mission from the Heliospheric community. The first to explore the Sun within distances of ~0.167 AU (or 25 million kilometers) at its perihelia. Its ancestors were the successful Helios -A and -B spacecraft, a pair of probes launched into heliocentric orbit for the purpose of studying solar processes, that orbited our star as close as 0.29 AU (or 43.432 million kilometers). However, PSP is a truly historic mission since it will scan – for the first time  – the actual atmosphere of the Sun, the corona. In turn, this will unavoidably broaden the horizons of the solar and heliospheric community, for the simple reason that we will go where we have never been before: to our home star. Thereby, all studies and concepts; all debates and different points of view will be validated and cross-compared giving ground to new knowledge !

The United Launch Alliance Delta IV Heavy rocket launches NASA’s Parker Solar Probe to touch the Sun, Sunday, Aug. 12, 2018 from Launch Complex 37 at Cape Canaveral Air Force Station, Florida.
Credit: NASA / Bill Ingalls

NASA named this mission after Eugene Parker, in order to honor his radical and at the same time fundamental contributions that revolutionized our understanding of how the Sun’s emissions affect our solar system through the solar wind.

The PSP mission exhibits a unique orbit. It utilizes the gravitational assist from Venus flyby for 7 times within a six-years duration (2025), leading to 24 perihelia. Each pass leads to a gradual “walking in” toward the Sun. The first flyby from Venus took place earlier this month (October 03, 2018) and the first perihelion will take place in less than two weeks time (November 06, 2018) making the Heliophysics community being in alertness, tuning in for the first ever close-up of the Sun’s surface !

Last month, in early September, each of PSP’s instrument suites powered on and returned their first observations on the spacecraft’s journey to the Sun. Although the data are not representative examples of the key science observations that shall be delivered by PSP, once the spacecraft is closer to the Sun, they demonstrated that all instruments are working well and that everything is properly set for the first rendezvous with our star !

The right side of this image — from WISPR’s inner telescope shows Jupiter in the distance (the bright object on the right). The left side of the image is from WISPR’s outer telescope that captured the Milky Way. Credit: NASA/Naval Research Laboratory/Parker Solar Probe

Following PSP, ESA is scheduling the launch of Solar Orbiter (SolO), currently foreseen for 2020. SolO will use gravity assists from Venus and Earth in order to get into a 168-day-long orbit around the Sun. SolO will get, up until a distance of 0.28 AU from the Sun, every five months. In the course of the mission, additional Venus gravity assist manoeuvres will be used to increase the inclination of SolO’s orbit, helping scientists to view for the first time the polar regions of the Sun clearly from an angle higher than 30 degrees. Thereby, the coordinated science objectives and the conjunction periods of SolO with PSP promote them to natural alleys working on the exploration of the Sun.

It seems that we are living in a golden age for the Heliospheric physics !

Cosmogenic Radionuclides – The quest of studying the solar activity of thousands of years

Cosmogenic Radionuclides – The quest of studying the solar activity of thousands of years

Thanks to the invention of the Neutron Monitor in 1948 and multiple spacecraft which monitor the cosmic ray environment since 1970’s we now have a constant record of the solar activity over almost 70 years. Information prior to this space era, however, are rare and take us back in time only to the late 1930s, when ionization chambers have been introduced. This of course allows us only a narrow view on the solar behaviour compared to the age of the Sun and our solar system and big scientific questions concerning, e.g., the current solar cycle can not be answered as easily. However, because galactic cosmic rays interact with the surrounding atmospheric constituents once they enter the atmosphere they are also able to induce the production of so-called cosmogenic radionuclides such as 10Be, 14C and 36Cl, with half-life times of up to 1.39 million years. Luckily, once mixed in the Stratosphere and Troposphere, these radionuclides get attached to aerosols and therewith transported to the surface. Here they are deposited in natural archives like ice sheets, tree rings or sediments, where the information of the solar activity is stored. Thus, cosmogenic radionuclides offer the unique possibility of obtaining a solar activity record over thousands of years. However, although cosmogenic radionuclide measurements can, thus, in principle be used to reconstruct solar activity back in time, in order to understand the underlying physical processes as detailed as possible the production of the cosmogenic radionuclides has to be studied numerically. As shown in Fig. 1, thereby a variety of complex physical processes has to be addressed, starting with the particle population of galactic cosmic rays in the local interstellar medium, their modulation within the heliosphere, their transport in the Earth’s magnetosphere as well as their interaction within the terrestrial atmosphere.

Prior to the end of 2012 the unmodulated galactic cosmic ray (GCR) flux, also known as the local interstellar spectrum (LIS), had not been measured in-situ. But with Voyager I crossing the outer heliosphere at around 122 AU for the first time measurements of the low energy LIS (below ~500 MeV) became available and the existing models on the production of cosmogenic radionuclides had to be revised.

Once GCR particles enter the heliosphere they encounter the heliospheric magnetic field (HMF) which is carried outwards by the solar wind. Thereby, the lower energy GCRs are modulated as they traverse the HMF. This transport can be described by the Parker transport equation, taking into account five important terms: the outward convection by the solar wind, gradient and curvature drifts in the global HMF, the diffusion through the irregular HMF, adiabatic energy changes due to the divergence of the expanding solar wind, as well as local sources (e.g., particles accelerated at the Sun). However, most often the much simpler analytical force-field approximation, which depends only on the solar modulation parameter Φ, is used in the literature. Furthermore, nowadays instruments like, e.g., PAMELA and AMS02 measure the high-energy GCR component above 10 GeV in the Earth’s vicinity, which is not influenced by the modulation due to the HMF. The energy spectrum of the energy range most important for the production of the cosmogenic radionuclides (0.4 – 8 GeV), however, is still unknown.

Figure 2: Upper panel: Annual variations computed with the IGRF model. Shown is the difference between the cutoff rigidities as they were present in 1900 and the ones of 2016. Lower panel: Comparison of the paleo-geomagnetic field reconstructions by different groups relative to present magnetic field strengths. Courtesy: K. Herbst

The HMF, however, is not the only magnetic filter that CRs encounter on their way to the Earth’s atmosphere. The Earth’s magnetic field also plays a major role when it comes to the modulation of the CR spectrum on top of the atmosphere. Although low- as well as high energy particles can enter the atmosphere at polar regions only high energy CRs can do so at equatorial regions. There is, however, not only a spatial but also temporal variation that has to be addressed. These changes can be of short term, e.g. due to a strong solar particle events, on the basis of annual variations (see upper panel of Fig. 2) but also centennial time scales (see lower panel of Fig. 2). Thus, such changes influence the primary particle spectrum on top of the atmosphere, and therewith the production of 10Be, 14C and 36Cl.

The main motor for the production of 10Be, 14C and 36Cl are galactic cosmic rays (GCRs) consisting of ∼87% protons, ∼12% alpha particles and ∼1% heavier particles (see e.g. Simpson, 2000). Once inside the Earth’s atmosphere CR induce the evolution secondary particle cascades of  muonic, electromagnetic as well as hadronic origin. In particular the high energy secondaries of the latter are able to further interact with the atmospheric Nitrogen, Oxygen and Argon atoms due to spallation reactions as well as thermal neutron capture producing the terrestrial 10Be, 14C and 36Cl isotopes. Thus, there is a clear anti-correlation to the solar activity. As a consequence, during high solar activity the production of cosmogenic radionuclides is low, and vice versa.

After stratospheric- and tropospheric mixing on time-scales in the order of around two (10Be) up to twelve years (14C) cosmogenic radionuclides are being attached to aerosols and finally deposited in natural archives like ice sheets, tree rings or sediments, where the information of the solar activity of thousands of years is stored. Existing radionuclide records thereby showed that GCRs most likely are not the only CRs contributing to the production of cosmogenic radionuclides. Recently, unexpected production rate increases around 774/5 AD and 993/4 AD in all three records were observed. This started a fruitful scientific debate about the causes of such strong increases. With a multi-radionuclide approach of highly resolved 10Be records combined with 36Cl ice core data, in 2015 different scientific groups independently could infer that enormous solar eruptions were the most likely causes behind the observations.

By combining numerical modelling and observations it is possible to reconstruct the solar activity (in form of the solar modulation parameter Φ) back in time. A reconstruction based on 10Be records by Muscheler et al. (2007) is shown in Fig. 3. Amongst others, thereby the reconstruction strongly depends on the LIS model the numerical simulations are based on.

Figure 3: Reconstruction of the solar modulation parameter from 10Be measurements based on Muscheler et al. (2007). Courtesy K. Herbst

Nevertheless, one feature can be seen in all records: the so-called Grand Solar Minima, in which the Sun showed unusually long solar minimum activity over tens of years. Shown here are the reconstructions between AD1000 and AD2005, where six of these minima have occured: Gleisberg (1880-1914), Dalton (1790-1820), Maunder (1645-1715), Spörer (1450-1550), Wolf (1280-1350) and Oort (1040-1080). This immediately implies that the low solar activity observed in the current solar activity cycle is not that uncommon, and that we are well within another small Grand Solar Minimum (referred to as Eddy Minimum).

Figure 4: Comparison of the 14C – based solar-modulation parameter with the revised sunspot (light blue) and group sunspot (blue) numbers. All records show an running 11-year average. The red curve shows the 4C (neutron monitor)-based results of the numerical production calculations. Courtesy K. Herbst

 

In order to test the results a comparison of the reconstructed solar modulation parameter values with the sunspot number, which is a direct measure of the solar activity, can be performed. As can be seen in Fig. 4, a reasonably good agreement can be found. Furthermore, because the solar modulation parameter mathematically can also be linked to the HMF it is also possible to reconstruct the heliospheric magnetic field strength back in time and compare actual observations with geomagnetic-, sunspot number- as well as 10Be-/14C- based reconstructions. As can be seen in Fig. 5 an impressive correlation between the different records has been found.

Figure 5: Composite plot of the reconstructed heliospheric magnetic field strength from 1390–2016 based on cosmogenic 10Be (McCracken and Beer 2015; 1391–1748), 14C (Muscheler et al. 2016; 1390–1748), the sunspot number (Owens et al. 2016a; 1749–1844), geomagnetic data (Owens et al. 2016a; 1845–1964), and from near-Earth observations in space (1965–2016). Courtesy K. Herbst

 

For more background information the reader is referred to the publications by: 

Beer, McCracken and von Steiger, Springer Business & Media (2012), https://doi.org/10.1007/978-3-642-14651-0

Muscheler et al. (2016), Solar Phys., https://doi.org/10.1007/s11207-016-0969-z

Cliver and Herbst (2018), Space Sci Rev, 214:56, https://doi.org/10.1007/s11214-018-0487-4

 

This post was writtend by Dr Konstantin Herbst

Dr Konstantin Herbst from the Christian-Albrechts-Universität zu Kiel, Germany

SunPy: a Python solar data analysis environment

SunPy: a Python solar data analysis environment

Introduction

For many years now we know that our star the Sun influences the Earth in many different ways, via the total solar irradiance, solar energetic particles and coronal mass ejections. Understanding the influence of the Sun on the Earth requires many different types of measurements. For example, NASA’s Solar Dynamics Observatory (SDO) spacecraft, produces over 1 terabyte of data per day (Pesnell et al., 2012), the bulk of it in the form of 4096 by 4096 pixel images in multiple bandpasses. The Parker Solar Probe (launched 12 August 2018) will fly closer to the Sun than any previous spacecraft, exploring the Sun’s corona, the solar wind and source and transport of space weather phenomena, by taking both in situ and remote measurements. Understanding the underlying physics requires sophisticated data analysis and modelling of multiple differing physical domains.

Managing and analyzing these heterogeneous data to answer evolving scientific needs and questions requires increasingly sophisticated software tools. These tools should be robust, easy to use and modify, have a transparent development history, and conform to modern software-engineering standards. The SunPy Project (SunPy Community et al., 2015) aims to provide a free and open source software package with these qualities for the analysis and visualisation of solar data. SunPy is built on Python, a free, general-purpose, powerful, and easy-to-learn programming  language. Python is widely used in many scientific fields, and has found applications in data analytics, machine learning and educational environments. SunPy brings solar physics in to the scientific Python ecosystem.

Organization and description of the code

Figure 1: SunPy is used to overlay two maps of data taken at the same time during the total solar eclipse of August 21, 2017: a ground-based photograph of the corona (black/white image), and an extreme ultraviolet image of the disk of the Sun (yellow image) taken by the SDO Atmospheric Imaging Assembly. Courtesy of S. Christe.

SunPy focuses on providing access to online repositories of solar physics data, and objects that make it easy to manipulate and display those data. SunPy is built using other open source Python projects, notably Astropy, numpy, SciPy, pandas and matplotlib. For example, many solar datasets are two-dimensional images, represented in SunPy by a Map object. Maps use SunPy’s coordinate transformation framework, an extension of Astropy’s powerful coordinates package, thereby enabling support for transforming between all Astropy and SunPy coordinate systems. SunPy was used to overlay ground based images of the solar corona taken during the total solar eclipse of August 21, 2017, and space based-images taken by SDO (Figure 1)

 

Figure 2: SunPy’s example gallery.

Figure 3: Simulated coronal loop emission generated using SunPy. Courtesy W. T. Barnes.

SunPy’s also provides the TimeSeries object for manipulating and displaying time-ordered scalar data.  Also, all public-facing SunPy functionality is unit-aware, meaning that physical units must be specified as required.  SunPy provides code snippets to get users started (Figure 2), and project members are active in teaching the community about SunPy.  SunPy is used by researchers working at NASA, European Space Agency (ESA), and the US National Solar Observatory Daniel K. Inouye Solar Telescope.  SunPy can also be used for modelling work: Figure 3 shows an example of using SunPy’s coordinate and mapping abilities to model the emission from an arcade of solar coronal loops.

 

Governance and development model

SunPy was born at the 2010 Solar Image Processing Workshop in Les Diablerets, Switzerland.  It is run by a small volunteer board of scientists that sets SunPy’s goals.  The Lead Developer (currently Dr. Stuart Mumford) is responsible for the implementation of SunPy’s goals. Contributions can be made by anyone. The project is managed at github.com/sunpy/sunpy, and unit testing, continuous integration, and community review of contributions are implemented to reduce bugs and maintain quality.  Students supported by the Google Summer of Code and the ESA Summer of Code in Space programs have made substantial contributions to SunPy.  The SunPy project is also a member of NumFOCUS, a US-based nonprofit organization that promotes sustainable high-level programming languages, open code development, and reproducible scientific research.

Future

SunPy gives users access to the ever widening scientific Python ecosystem. SunPy 1.0 is under development for release later on this year. This version will use Astropy’s representation of time, bringing improved precision and leap second support to SunPy.  The usability of SunPy’s data acquisition infrastructure will also be improved.  SunPy 1.0 will also drop support for the Python 2 series and require Python 3.6 or higher.  SunPy is also developing NDCube, a multi-dimensional, physically aware data object that can represent more complex multi-dimensional datasets, such as that from NASA’s Interface Region Imaging Spectrometer (IRIS) and other spectrometer instruments.  Finally, SunPy’s affiliated package program encourages the development of SunPy-based code that performs specific scientific tasks such as analyzing solar radio spectra.

References

SunPy Community, S.J. Mumford, S. Christe, et al. 2015, Computational Science and Discovery, 8, 014009.

D. Pesnell, B. J. Thompson, and P. C. Chamberlin. The solar dynamics observatory (SDO). Solar Physics, 275:3–15, Ja

Jack Ireland, lead support scientist at NASA/GSFC and Communications Officer for SunPy Project

nuary 2012.

 

This blogpost is written by Jack Ireland from the SunPy Community

Cosmic rays – messengers from space

Cosmic rays – messengers from space

Cosmic rays (CRs), are not actually rays, but highly energetic charged particles of extraterrestrial origin. The life cycle of a cosmic ray particle starts with its birth at some point in the Universe, its travel at nearly the speed of light and finally with its death ( e.g. at a detector). These highly energetic particles strike our planet from all directions and thus provide a constant background. In practice, this means that thousands of cosmic ray particles pass through our bodies every minute, but the resulting radiation imprint is relatively low if we compare this to the natural background radiation.

Sources of CRs, encompass the Sun, our Galaxy and beyond. As a result, these charged particles span almost ~35 orders of magnitude in flux and ~14 orders of magnitude in energy. This, means that we need many different experimental devices (e.g. spacecraft data, neutron monitors, muon telescopes, AMS02, PAMELA, TRACER, IceTop, Pierre Auger Observatory and many more) to capture the entire spectrum of CRs and at the same time this offers many opportunities to evolve our experimental/detection set ups and our understanding.  We measure the energy of CRs in eV (electron-Volt: it corresponds to the energy gained when an electron is accelerated through a potential difference of 1 volt). Based on the energy of CRs, we can identify the origin and map different parts in the spectrum. For example, above a few GeV/nucleon, the energy spectrum of CRs follows a power law proportional to E−2.7. At 1015 eV there is a break in the spectrum, which is typically referred to as the “knee”, below this energy CRs are of Galactic origin. From the “knee” up to 1018 eV the power law falls as E−3.1. A second break in the spectrum occurs at 1018 eV, usually called the “ankle”, where the spectrum flattens. At this energy it is possible that the particles can be of extragalactic origin. The CR spectrum continues up to 1020 eV, which is the current high-energy limit for CR observations.

The spectrum of CRs, denoting the different components and sources (Credit: A. Papaioannou, adopted from the CR spectrum by S. Swordy).

Low energy (up to ~1015eV) Galactic CRs (GCRs) are most likely accelerated in supernovae (SN) shock waves which occur approximately once every 50 years in our Galaxy. GCRs are the only matter originating from outside our solar system that can be studied directly. Thereby, their composition and energy spectra can be used to determine their sources, acceleration mechanisms and transport processes in the Galaxy. However, since CRs are charged particles those are deflected by magnetic fields. This, in turn, obscures the identification of their actual source, since their travel paths have been randomized.

At the same time the Sun is an additional sporadic source of energetic particles, often termed as solar CRs (SCRs) and/or Solar Energetic Particles (SEPs).  These particles are accelerated by shock waves driven by coronal mass ejections (CMEs) traveling through the corona, and by the magnetic energy that is released in solar flares. When a CME occurs 100 million tons of hot coronal gas is suddenly ejected into space at speeds of 1.6 million km per hour. SFs are observed in white light, UV, soft and hard x-rays, gamma-rays, neutrons and radio waves and hence cover the entire electromagnetic spectrum. When CRs penetrate into our solar system, those are affected by the interplanetary magnetic field (IMF), which is  embedded in the solar wind blowing from the Sun. Therefore CRs have difficulty reaching the inner solar system and Earth. Solar activity (and the rate of CMEs and SFs) varies over the 11 year solar cycle, leading to a variation in the intensity of CRs at Earth, in anti-correlation with the solar activity (as represented by the sunspot number). Furthermore, the interplanetary counterparts of propagating CMEs reduce the GCRs flux, leading to a decrease known as the Forbush decrease.

The heliospheric enviroment. Inserts include, an artistic representation of the Sun-Earth relations (Credit: NASA), a solar flare (SoHO/EIT), a coronal mass ejection (SoHO/LASCO), the recent Solar Energetic Particle (SEP) event from 10 September 2017 and the corresponding recordings from spacecraft (GOES) and neutron monitors on the ground (Ground Level Enhancement – GLE; NMDB) (Credit: A. Papaioannou)

If CRs are energetic enough and reach the Earth’s atmosphere, undergo collisions with its atoms and produce a cascade of secondary CR particles that shower down through the atmosphere to the Earth’s surface. These secondary CRs include pions, electrons and positrons. The number of particles that reach the Earth’s surface is related to the energy of the primary CRs that made it to the upper atmosphere. The deeper the particles penetrate into the atmosphere, the more energy they lose.  A SF and/or a CME may result to an intense flux of SCRs, which gives ground to an SEP and when recorded on the Earth’s surface, to a Ground Level Enhancement (GLE).

GCRs, being messengers from space, hold a key for the greater understanding of our universe, since the most exciting frontiers of astrophysics involve physical processes and environments that are not reproducible in the laboratory. In addition, CRs carry information from their interaction with the magnetic irregularities they encounter en route to the Earth and help us track our heliospheric environment. They also quantify the radiation levels encountered by air crews on flight altitudes and by astronauts in space.  

A synthesis of different figures showing the RAD on MSL on the surface of Mars; RAD’s field-of-view and the corresponding parts of the detector, as well as , the historical photo of Victor Hess in a ballon en route to the discovery of cosmic rays (Credit: A. Papaioannou, using figures from this presentation)

In August 2012, 100 years since the discovery of CRs from Victor Hess, the Radiation Assessment Detector (RAD) onboard the Mars Science Laboratory (MSL) measures for the first time CRs on the surface of another planet.

A thrilling new era has already began !

 

How do we study the magnetosphere?

How do we study the magnetosphere?

Our closest star, the Sun, is constantly emitting hot gas in all directions as its upper atmosphere, the corona, expands. This is known as the Solar Wind, also carrying with it an embedded magnetic field, the Interplanetary Magnetic Field (IMF).  The IMF originates  at the Sun and forms an enormous spiral throughout the solar system as the solar wind escapes radially, while the magnetic field-lines are anchored to the rotating Sun. This is the large-scale environment, or the laboratory, for a magnetospheric physicist. The core of magnetospheric physics is to increase our understanding of the complex interactions occurring when a magnetized planet is exposed to this solar wind and IMF environment. This blog-post will briefly mention some of the ways we study this interaction, and what kind of questions we try to answer about the solar wind – magnetosphere system.

First of all, what is a magnetosphere? A magnetosphere is the region around a magnetized planet where the magnetic field is the one related to the planet itself. The other magnetic domain is the one only connected to the Sun or solar wind, referred to as the IMF in this context. As for the Earth, the boundary between the Earth’s magnetic field and the IMF field-lines is rather sharp. On the dayside, this boundary, known as the magnetopause, usually sits at about ~10 Earth radii toward the Sun at the subsolar location, and wrap around to form a blunt surface that define the magnetosphere, as seen in the image above, forming a long tail in the anti-sunward direction.

When the solar wind and the IMF interact with the magnetosphere a variety of processes take place. Most interesting – when it comes to energy and momentum transfer into the magnetosphere system –  is the magnetic interactions, initially taking place at the dayside magnetopause. Through a process known as magnetic reconnection, field-lines initially connected only to the planet can merge with the incoming IMF to form field-lines magnetically coupled both to the planet and to the Sun/solar wind. This allows these newly opened field-lines to be pulled tailward by the solar wind, while still being anchored to the Earth. This is how most of the solar wind energy enter the magnetosphere system, which could reach values of Terra Watts during geomagnetic storms. A consequence of the dayside reconnection process is that the reservoir of field-lines connected only to Earth is continually reduced. The magnetosphere’s way of solving this problem is through creating new field-lines that have both their footprints anchored to the planet, again through the process of magnetic reconnection. This happens deep within the magnetotail, and causes momentum and energy to be transported toward the planet, responsible for a variety of phenomenon that we can see and measure on the ground at Earth. Most notable are the aurora borealis and -australis visible in bands around the magnetic poles, and associated magnetic disturbances. Interestingly, the entry of the solar wind plasma (particles) itself into the magnetosphere is not very important in describing the aurora. The accelerated particles causing the aurora largely originate from within the system although their energy come from the solar wind.

Nighside aurora seen from the EISCAT Svalbard radar site. Credit: Jone Peter Reistad.

When studying the magnetosphere, a large variety of instruments are being used. One can distinguish between two types of measurements that complement each other, to a large degree. To measure the influence from a large region of the mangetosphere simultaneously, remote sensing techniques are applied. One example of such is observations of the aurora, where the light originate from the high latitude ionosphere at typically 100-200 km. Since the magnetic field at high latitudes map out to very large regions of the magnetosphere, the aurora can be interpreted, to some extent , as a screen illuminating the more distant magnetospheric processes. Therefore, by studying the high-latitude electrodynamics close to the ground, one can infer properties of the much larger magnetosphere. The other type of measurements is in-situ observations of physical quantities such as electric and magnetic fields/waves and charged or neutral particles. This is usually obtained from satellites orbiting within the magnetosphere. One major challenge when interpreting such data in terms of the big system is that they only provide point measurements in a huge system. Also, temporal and spatial variations are in general mixed, as stationary is difficult to obtain/determine. Hence, remote-sensing and in-situ measurements addresses different spatial scales and often different processes in the magnetosphere system, and act  complementary to each other in order to obtain increased knowledge of how the system works. Recent missions that has greatly contributed to increase the understanding of the solar wind – magnetosphere – ionosphere interactions include Cluster, THEMIS, Swarm, Van-Allen Probes, and MMS.

Although we have learned a lot, especially through the space age, of how the solar wind and IMF environment affect the mangetosphere, many questions still remain. One example is the very nature of the reconnection process, which is a fundamental plasma process allowing efficient energy transfer into the system. A dedicated mission, the Mangetospheric Multiscale Mission was recently launched to investigate its details by probing the reconnection region at finer spatial scales than ever before by 4 closely separated spacecrafts. At present, most models describing the large-scale distributions of the important parameters in our system are indeed very static. We know that the reality is highly dynamic and structured, and it remains as an outstanding challenge to further enhance our understanding of the complexities in our system to be able to more accurately predict the outcome of the solar wind – magnetosphere – ionosphere interactions.

Eyes on the Sun

Eyes on the Sun

The Sun is a complex, dynamic ball of plasma which influences our lives. Studying the Sun is challenging because each of its layers have different composition, physics and wavelengths of emssion. Moving outwards from the photosphere (visible surface of the Sun), we have the chromosphere and the corona (hottest outermost layer). The solar plasma is in constant motion much like fiercely boiling water. To make matters worse, gigantic planet sized eruptions frequently play havoc with space-based instruments and communications.

To understand the workings of the Sun, solar physicists look through the eyes of 21 ground-based telescopes, 8 space-based observatories, dozens of radio telescopes, X-ray detectors, and many high altitude platforms that collect particles emitted by the sun. Optical astronomy, spectroscopy and magnetic field measurements are the most common techniques used.

The most common ground-based observations are taken with Hydrogen-alpha and Calcium-II filters. The Sun’s chromosphere is abundant in these elements/ions and emits light in these wavelengths. Chromospheric features such as spicules, prominences (i.e., jets, protrusions of plasma respectively) etc. are studied using these observations. The Sun’s hot corona emits light in UV and EUV wavelengths. Since emissions in this range are absorbed by the Earth’s atmosphere, we rely heavily on space-based observatories to study coronal loops, flares etc. The variety of structures on the Sun and the different layers of the Sun are abundant in specific elements/ions. The stunning images from different filters (see fig 1) provide unique ways to probe the depths of our amazing Sun. Simultaneous images from the 9 filters onboard NASA’s Solar Dynamics Observatory has been revealing secrets of our dynamic Sun since 2012.

Optical telescopes are easy to build but only give us the overall view of the Sun. The temperature, ionization state, density, magnetic/electric fields, speed/direction of motion all influence the emission from a particular plasma. We require spectroscopic data to extract this information. Spectral profiles can also give us indication of unresolved structures. The latest spectrograph in the sky is NASA’s Interface Region Imaging Spectrograph. Although spectrographs provide a large dose of information, they are limited by field-of-view and downlink bandwidth. Scientists therefore need to compromise on the number of wavelengths or area of observation when using spectrographs, restricting their progress.

Fig. 2: Composite image showing multi-temperature plasma. Cool 60,000 K plasma in red and hot 1 MK plasma in blue and green Credits: NASA/GSFC/SDO

The Sun’s 22-year magnetic cycle is another mystery pending to be solved. Manifestations of the magnetic field result in solar activity. Unambiguous measurements of the magnetic field are currently possible only in the photosphere. Scientists are engaged in developing indirect techniques to measure magnetic field in the higher solar atmosphere. Solar Orbiter, joint venture by ESA and NASA, will, for the first time, clearly measure the magnetic field strength near the poles of the Sun. This will improve solar models and advance our knowledge of the solar dynamo and the reversal of the global magnetic field.

Learning about the Sun will not only enhance our capabilities of predicting space weather, which can disrupt our daily lives but also strengthen our knowledge about other stars. The Sun is our closest star and we cannot study any other star in as detail as we can the Sun. Studying our “Sun as a star” will help us extrapolate the knowledge to other stars. How stars interact with the worlds around them is a relevant topic in sight of the search for extra-terrestrial life. We could also determine what will become of our planet and us eventually.

Capturing a Whole Total Eclipse of the Sun: Megamovie

Capturing a Whole Total Eclipse of the Sun: Megamovie

by Hugh S Hudson (U. of Glasgow and UC Berkeley)

Normally solar eclipses give an observer only a fleeting moment (minutes at most) to enjoy the solar corona. We aim to amplify that considerably in the August 21 eclipse across North America. The plan is simple: Megamovie will capture everybody’s images, especially those from a group of 1,000 photographc volunteers, and compile them into an open-source archive that (weather permitting) will span an hour and a half of the corona’s life. One can find this program at the URL “eclipsemega.movie“, and in the  smartphone app “Eclipse Megamovie Mobile“.

The path of totality crosses the entire continent of North America, well-populated with eager observers equipped with the latest things in consumer electronics – marvelous cameras plus GPS and the Internet. The previous occurrence, in 1918, had none of that.  The program is thus a citizen-science project, embracing all levels of experience and capability among the observers, and at the same time it will produce a systematic record that we believe will be the first of its kind, and certainly can be the largest. We intend to follow up with citizen-science analysis projects, along the lines of SETI@Home and Zooniverse, to make sense of the very complicated records.

Megamovie does new and original things that will create real science. For the corona, the existence of the archive itself is unique.  Here we will have vast oversampling in the time domain, with access to disturbance modes on short time scales seldom observed with such resolution. Here we expect to see waves and flows in the low corona, by following the intensity variations of discrete features. Of course the Megamovie archive can extend to time scales of tens of minutes, where we know that large-scale structures will show perceptible and dynamically interesting motions. How much does a streamer wobble, and in what mode?

A CME and other structures captured in eclipse observations by Hanaoka et al. (2013); the left panel is an edge-enhanced view of one stacked image at 12-Nov-2012 20:39 UT. The right panel is a difference against observations from a different site at 21:14 (this is a cropped version of Figure 1 of the manuscript used by permission from Dr Y. Hanaoka)

The uniqueness of the August 21 eclipse continues with the coincidental presence of the bright star Regulus. This reference point will show up in all of the deep coronal images. In addition we have recently achieved precise astrometric information about the Moon, derived from the Kaguya and Lunar Reconaissance Orbiter missions; this eclipse will be the first major opportunity to apply this new information to eclipse data and the Sun.

The star field at the time of the August 21, 2017 eclipse,showing the position of the Sun as it moves during totality, and also the nearby bright star Regulus. (Figure provided by H. Hudson)

These advantages should make it possible to analyze and correct many images at a precision  rivaling that of the famous Eddington observations in 1919. We note that this historically important confirmation of general relativity has been repeated with modern detectors such as those found in everyday consumer electronics now. The Megamovie Mobile app (free) provides many resources for smartphone users; the mere timing of Baily’s Beads will make a systematic recording of the shadow path and thereby the local instantaneous radius of the Sun. The app does this automatically, and even without a cheap telephoto attachment, a smartphone camera can get wonderful timing information with precise GPS metadata.