Solar polar fields dominate the large-scale structure of the corona during most of the solar cycle, and seem to be indicators -if not precursors- of the magnetic activity in the next cycle. On the other hand, the large-scale flows at high latitudes play an important role in flux transport dynamos, but are still poorly constrained by observations. Thus, the solar poles are the object of desire of helioseismologists, solar cycle forecasters and flux transport modelers alike. The caveat is that the physical properties at the poles are hard to characterise because of the weak nature of the magnetics fields and the almost unsurmountable projection effects as seen from the Earth’s vantage point. This session will review the advances in the measurement and understanding of solar polar fields and flows, and their connection to the Solar Cycle. It will also explore the benefits that will come from complementing SDO data with other new and existing observatories, in the advent of DKIST, PROBA2 and Solar Orbiter.
Plenary speaker: Sarah Gibson (HAO)
13:15 | Beyond Flatland: A Star of Many Dimensions | Gibson, S | Invited Oral |
| Sarah Gibson |
| NCAR/HAO |
| The more we have learned about the Sun, the more we can appreciate its essential complexity. Telescopes confirmed that it was not an unblemished sphere. Multi-wavelength observations revealed its structured atmosphere, and ever-higher resolution exposed its spectacular dynamics. Helioseismology penetrated its depths, and STEREO views gave us our first three-dimensional perspective. With Solar Orbiter we will finally leave our ecliptic bias behind and see the Sun from high latitudes. What will we see? And what could we see if future missions dwell at near-polar vantages, providing a synoptic view from above or below? The science enabled by such viewpoints is broad and deep, with potential both to finally fill known gaps in our understanding, and to reveal hitherto undiscovered aspects of the Sun and heliosphere. |
13:45 | The EUI instrument onboard Solar Orbiter: the EUV corona imaged differently | Berghmans, D | Oral |
| David Berghmans [1], Pierre Rochus [2], Frédéric Auchère [3], Louise Harra [4], Werner Schmutz [5], Udo Schühle [6] |
| [1] Royal Observatory of Belgium (B), [2] Centre Spatial de Liège (B), [3] Institut d'Astrophysique Spatiale (F), [4] UCL-Mullard Space Science Laboratory (UK), [5] PMOD World Radiation Center (S), [6] MPI for Solar System Research (G) |
| The ESA Solar Orbiter mission is designed to determine how the Sun creates and controls the heliosphere. The spacecraft will bring a combination of in situ and remote sensing instruments out of the ecliptic (>30°) and close to the sun (0.3 solar-radii). The launch of Solar Orbiter is expected (not earlier than) Feb 2019. The Extreme Ultraviolet Imager is part of the remote-sensing package of Solar Orbiter, to be operating during 3 ten-day periods of each orbit around the Sun, which last roughly half a year. These 3 periods will correspond to perihelion and maximal solar latitude north and south. The Extreme Ultraviolet Imager is itself a suite of three UV and EUV telescopes that observe the solar atmosphere both globally as well as at very high resolution.
The two high-resolution imagers (HRIs) will image the solar atmosphere in the chromospheric Lyman alpha line and the coronal 17nm pass band with a resolution of 0.5 arcsec. From perihelion, this will correspond to a pixel footprint on the solar disc of (110km)^2 . The Full Sun Imager (FSI), working at the 17.4 nm and 30.4 nm EUV passbands, will provide a global view of the solar atmosphere and is therefore an essential building block for the “connection science” of the Solar Orbiter mission. The FSI field of view is large enough (228arcmin) that, even at perihelion and at maximal off-points by Solar Orbiter, the full solar disk remains in the field of view. This large FOV and the FSI’s high sensitivity will allow to image the “transition corona” where the topology of streamers and pseudo-streamers fades in the solar wind. Furthermore, FSI will be the first to image all this from out of the ecliptic.
In this talk we will give an overview of the EUI instrument. We will focus on the novel aspects of EUI that will allow it to image beyond what previous EUV imagers could show us: EUV imaging from the highest solar latitude, with the widest field-of-view and at highest spatial resolution. |
14:00 | Solar EUV Irradiance Monitoring beyond SDO-EVE: GOES EXIS Preliminary Measurements and Validation | Eparvier, F | Oral |
| Francis Eparvier [1], Andrew Jones [1], Thomas Woods [1], Martin Snow [1], Edward Thiemann [1], William McClintock [1], Donald Woodraska [1], Janet Machol [2,3], Rodney Viereck [4], Thomas Eden [1], Steven Mueller [1], Randle Meisner [1] |
| [1] University of Colorado - LASP, [2] University of Colorado - CIRES, [3] NOAA - NCEI, [4] NOAA - SWPC |
| Starting with the recently launched NOAA GOES-16, the future of solar extreme ultraviolet (EUV) and soft x-ray (XUV) irradiance monitoring for the next few decades will be with the EUV and X-Ray Irradiance Sensors (EXIS). EXIS consists of the X-Ray Sensor (XRS) and the EUV Sensor (EUVS). The updated XRS continues NOAA’s 40+ year history of flare observations in the 0.1-0.8 nm and 0.05-0.4 nm bands. The new EUVS design makes measurements of specific solar emission features that span the range of temperatures and variability in the source regions of EUV in the solar atmosphere, namely He II 25.6 nm, Fe XV 28.4 nm, He II 30.4 nm, C III 117.5 nm, H I Ly-alpha 121.6 nm, C II 133.5 nm, Si IV / O IV 140.5 nm, and the Mg II C/W feature centered around 280 nm. This collection of measurements allows for the modeling of the full EUV spectrum (see the presentation by E.M.B. Thiemann, et al. for details of the model). This presentation will give an overview of the preliminary measurements and data products from the GOES-16 and -17 EXIS instruments and comparisons and validations with other measurements (SDO-EVE, SORCE, TIMED-SEE and previous GOES). |
14:15 | The High-Resolution Coronal Imager 2.1 | Rachmeler, L | Oral |
| Laurel A Rachmeler [1], Amy R Winebarger[1], Sabrina L Savage[1], Ken Kobayashi[1], and the rest of the Hi-C team. |
| [1]NASA Marshall Space Flight Center |
| On May 29, 2018 the High-Resolution Coronal Imager successfully launched from White Sands Missile Range and gathered over five minutes of coronal images in the EUV. This Hi-C 2.1 version has been modified from the original instrument to observe at a peak wavelength of 17.2 nm, and includes a custom-build low-noise camera. The 260 x 260 arcsec FOV of Hi-C 2.1 targeted NOAA Active Region 12712 during this flight, and coordinated observations were taken with IRIS, XRT, EIS, AIA, and HMI as well as numerous ground-based telescopes. The primary science goals of Hi-C 2.1 are to study the coronal counterparts of type II spicules and explore the relationship between chromospheric and coronal heating in active region cores. We present an overview of the Hi-C 2.1 instrument and the data acquired during flight. |
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New HMI Data Series: temporally consistent disambiguation for HARP vector magnetic field timeseries data | Barnes, G |
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Graham Barnes[1], KD Leka[1], Eric Wagner[1] |
[1]NWRA |
The last step of the HMI pipeline removes the 180 degree ambiguity in the direction of the field transverse to the line of sight, enabling users to download physically meaningful components of the photospheric vector field. However, for the pipeline, each time is treated independently, which can lead to changes in the direction of the transverse field from one time to the next that are unphysical. These changes result in large values of the time derivative of the inferred surface magnetic field vector, and hence spurious changes in quantities such as flows and electric fields computed from it. NWRA has developed an enhanced version of the disambiguation code that includes a temporal consistency term. We compare the results of the new method to the results of the pipeline code and demonstrate the improvement in temporal stability. A new data product with the time-series disambiguation is being made available to the community through the JSOC for selected HARPS.
This material is based upon work supported by NASA under award Nos. 80NSSC18K0055 and 80NSSC18K0180. |
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NuSTAR’s observations of tiny flares and big eruptions | Hannah, I |
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Iain Hannah[1], Brian Grefenstette[2], Lindsey Glesener[3], Sam Krucker[4,5], David Smith[6], Hugh Hudson[1,4], Stephen White[7], Matej Kuhar[5] |
[1]Glasgow, [2]Caltech, [3]Minnesota, [4]Berkeley, [5]FHNW, [6]Santa Cruz, [7]AFRL |
NuSTAR is an astrophysics X-ray telescope, with direct imaging spectroscopy providing a unique sensitivity for observing the Sun above 2.5keV. Targeting the faintest X-ray emission from the solar atmosphere allows the study of the smallest flares, and their contribution to heating the corona. However, it can also be used to observe weak high-coronal sources that are associated with the energy release in large, but occulted, eruptions. NuSTAR has observed the Sun over a dozen times since Sep 2014, through to our latest observations in 2018: see http://ianan.github.io/nsovr/ for a quicklook overview of NuSTAR’s solar observations. We will present some of the latest solar observations with NuSTAR and compare them to the emission seen at lower energy wavelengths, particularly in EUV with SDO/AIA and also the derived Fe18 emission. |
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The butterfly diagram and tilt angles obtained from the Horrebow sunspot observations | Valliappan, S |
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Senthamizh Pavai Valliappan [1], Rainer Arlt [1], Christoffer Karoff [2,3], Carsten Sønderskov Jørgensen [3] |
[1] Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany, [2] Department of Geoscience, Aarhus University, Høegh-Guldbergs Gade 2, 8000, Aarhus C, Denmark, [3] Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000, Aarhus C, Denmark |
The solar dynamo is not fully periodic (and monotonous) as the solar cycles exhibit mild to extreme variability in their characteristics. The study of properties of sunspots over centuries may enable deeper understanding of the solar dynamo and to predict the next solar cycles. The scattered records of sunspot observations, since the invention of the telescope, are not completely inspected yet. The discovery and analysis of many old records of sunspot observations are currently ongoing and they reveal interesting properties of solar cycles. We are currently analyzing the record of sunspot observations by Christian Horrebow from the Copenhagen observatory during 1761 – 1777. The sunspot record by Horrebow has already been analyzed by Thiele (1859), Wolf (1873), and Hoyt & Schatten (1995), but they only studied the sunspot numbers. However, the sunspot record also contains the positions of sunspots, even though not the area measurements, which we are analyzing now. The positions of sunspots are very important parameters in constraining the solar dynamo, in particular the tilt angles of sunspot groups can be calculated if the individual sunspot positions are available. The tilt angles of sunspot groups are also an important parameter in the flux transport dynamo model, in which it determines the evolution of the polar field which in turn determines the properties of next solar cycle. In Horrebow’s sunspot record, the positions of sunspots are given in tables containing the horizontal position readings in units of sidereal time, corresponding to the passage to the solar disk, and the vertical position readings in screw turns of the instrument used. The butterfly diagram is constructed with the obtained positional readings of sunspots for the solar cycles 1 (maximum), 2, and 3 (beginning). We group the sunspots into groups and then calculate the tilt angles of sunspot groups. The sunspot positions and tilt angles for cycles 1 – 3 are also available independently from the sunspot drawings of Staudacher, which are comparatively not very precise and lack orientation but cover a longer period than Horrebow’s. The properties of solar cycles from two independent records are compared and the reliability of Staudacher’s drawings is determined. |
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The Role of the Solar Soft X-ray Irradiance on Thermospheric Chemistry and Structure | Samaddar, S |
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Srimoyee Samaddar[1], Karthik Venkataramani[2], Scott Bailey[3] |
[1]Virginia Polytechnic Institute and State University, [2]Virginia Polytechnic Institute and State University, [3]Virginia Polytechnic Institute and State University |
The solar soft x-ray irradiance deposits energy into the lower thermosphere, thus playing a significant role in the photochemistry and E-region ionosphere. Since the irradiance varies strongly with solar activity, it is imperative to incorporate this variability in models predicting the earth’s thermosphere. In this talk, we use the recently developed ACE1D model to explore the role of solar soft x-rays on temperature, chemistry, and the overall structure of the thermosphere.
The ACE1D model produces a global average thermosphere by self- consistently solving the one-dimensional continuity equations to obtain the ions and neutral densities and the energy equations to obtain the ions, neutral and electron temperatures. A combination of solar and magnetospheric fluxes and joule heating is used as energy inputs to the model.
We show that solar soft X-rays are the dominant driver of globally averaged nitric oxide densities. We further find that the soft x-rays have a very large impact on temperature throughout the thermosphere, even though their energy is deposited low in the thermosphere. We show that this is due to the heat exchange from non-thermal electrons which plays a significant part in energy dynamics of the thermosphere.
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New and Improved Mode Fitting Results | Korzennik, S |
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Sylvain G. Korzennik |
Harvard-Smithsonian Center for Astrophysics |
I present the most recent improvements to my mode fitting procedures, and how
they affect inferred properties of the Sun. The fitting has now been extended
to $\ell=0$ modes, and in the process to more $\ell=1$ modes. Close scrutiny
of these low degree modes revealed the need to change the scaling of the error
bars on the derived multiplet quantities. I fitted a test data set using
different leakage matrices, including one set computed to fit very long time
series and therefore uses for $B_o$ the value of $5.0593^o$ (or
$\sqrt{|Bo^2|}$). I show how that leakage matrix is different from the one
computed in the past for very long time series ($B_o=0$) and its impact on the
fitted parameters. |
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Variation in Sun's Seismic Radius and its implication on the TSI variability | Tripathy, S |
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Kiran Jain, Sushanta Tripathy, Frank Hill |
National Solar Observatory, Boulder, Co 80303 USA |
Space-borne instruments on-board SoHO and SDO have been collecting uninterrupted helioseismic data since 1996 and are providing a unique opportunity to study changes occurring below the surface over two solar cycles, 23 and 24. Here we study the variation in solar seismic radius with the changing level of the surface magnetic activity. The seismic radius is calculated from the fundamental modes of solar oscillations utilizing the observations from SoHO/MDI and SDO/HMI. Our study suggests that the sub-surface layers shrinks with increasing magnetic activity. We interpret these changes in seismic radius to be caused by the variation of sound speed, temperature or the changes in the super-adiabatic superficial layers. Our estimated maximum change in seismic radius during a solar cycle is about 5 kilometers, and is consistent in both solar cycles 23 and 24. We also explore the relationship between seismic solar radius and the total solar irradiance (TSI) and find that the radius variation plays a secondary role in TSI variability. We further observe that the solar irradiance increases with decreasing seismic radius, however the anti-correlation between them is moderately weak. |