Photospheric magnetic topology of a north polar region

Aims. We aim to characterise the magnetism of a large fraction of the north polar region close to a maximum of activity, when the polar regions are reversing their dominant polarity. Methods. We make use of full spectropolarimetric data from the CRisp Imaging Spectro-Polarimeter installed at the Swedish Solar Telescope. The data consist of a photospheric spectral line, which is used to infer the various physical parameters of different quiet Sun regions by means of the solution of the radiative transfer equation. We focus our analysis on the properties found for the north polar region and their comparison to the same analysis applied to data taken at disc centre and low-latitude quiet Sun regions for reference. We also analyse the spatial distribution of magnetic structures throughout the north polar region. Results. We find that the physical properties of the polar region (line-of-sight velocity, magnetic flux, magnetic inclination and magnetic azimuth) are compatible with those found for the quiet Sun at disc centre and are similar to the ones found at low latitudes close to the limb. Specifically, the polar region magnetism presents no specific features. The structures for which the transformation from a line-of-sight to a local reference frame was possible harbour large magnetic fluxes (>1017 Mx) and are in polarity imbalance with a dominant positive polarity, the largest ones (>1019 Mx) being located below 73° latitude.

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Magnetic topology of the north solar pole

Astronomy and Astrophysics ◽

10.1051/0004-6361/201832751 ◽

2018 ◽

Vol 616 ◽

pp. A46 ◽

Cited By ~ 3

Author(s):

A. Pastor Yabar ◽

M. J. Martínez González ◽

M. Collados

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Field Vector ◽

Line Of Sight ◽

Small Scale ◽

Quiet Sun ◽

The North ◽

Field Distributions ◽

Disc Centre ◽

The Magnetic Field

The magnetism at the poles is similar to that of the quiet Sun in the sense that no active regions are present there. However, the polar quiet Sun is somewhat different from that at the activity belt as it has a global polarity that is clearly modulated by the solar cycle. We study the polar magnetism near an activity maximum when these regions change their polarity, from which it is expected that its magnetism should be less affected by the global field. To fully characterise the magnetic field vector, we use deep full Stokes polarimetric observations of the 15 648.5 and 15 652.8 Å FeI lines. We observe the north pole as well as a quiet region at disc centre to compare their field distributions. In order to calibrate the projection effects, we observe an additional quiet region at the east limb. We find that the two limb datasets share similar magnetic field vector distributions. This means that close to a maximum, the poles look like typical limb, quiet-Sun regions. However, the magnetic field distributions at the limbs are different from the distribution inferred at disc centre. At the limbs, we infer a new population of magnetic fields with relatively strong intensities (~600−800 G), inclined by ~30° with respect to the line of sight, and with an azimuth aligned with the solar disc radial direction. This line-of-sight orientation interpreted as a single magnetic field gives rise to non-vertical fields in the local reference frame and aligned towards disc centre. This peculiar topology is very unlikely for such strong fields according to theoretical considerations. We propose that this new population at the limbs is due to the observation of unresolved magnetic loops as seen close to the limb. These loops have typical granular sizes as measured in the disc centre. At the limbs, where the spatial resolution decreases, we observe them spatially unresolved, which explains the new population of magnetic fields that is inferred. This is the first (indirect) evidence of small-scale magnetic loops outside the disc centre and would imply that these small-scale structures are ubiquitous on the entire solar surface. This result has profound implications for the energetics not only of the photosphere, but also of the outer layers since these loops have been reported to reach the chromosphere and the low corona.

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The evolution of Jupiter polar cyclones

10.5194/egusphere-egu21-16226 ◽

2021 ◽

Author(s):

Alessandro Mura ◽

Christina Plainaki ◽

Giuseppe Sindoni ◽

Alberto Adriani ◽

Davide Grassi ◽

...

Keyword(s):

Polar Region ◽

Infrared Camera ◽

Polar Regions ◽

The South ◽

The North ◽

Rest Position ◽

North Polar ◽

The Stability ◽

Westward Drift ◽

Juno Mission

JIRAM (the Jovian InfraRed Auroral Mapper) is an infrared camera and spectrometer on board Juno. JIRAM operates in the 2-5 &#956;m spectral range and is built to observe both Jupiter's infrared aurora and its atmosphere. Since 2016, JIRAM has performed several observations of the polar regions of the planet, thanks to the unique orbital design of the Juno mission.&#160; In the north polar region, Juno discovered, in 2017, the presence of an eight-cyclone structure around a single polar cyclone; to the south, a polar cyclone is surrounded by five circumpolar cyclones. The stability of these structures has been monitored for almost 4 years. Recent observations, made at the end of 2019, showed that the configuration of the South Pole has temporarily changed: the structure moved in a hexagon for a few months, before returning to its original pentagonal shape. To the north, there are significant hints that the octagonal shape may have been lost for a similar period of time. We find that all cyclones show a very slow, westward drift as a rigid ensemble, and, in addition, they oscillate around their rest position with similar timescales. These oscillations seem to propagate from cyclone to cyclone. The implications of these transient deviations from the symmetrical forms, which appear to be an apparent condition of equilibrium, are discussed.

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Morphometry and temperature of small sub-10 km craters at Mercury’s northern pole: Implications for source and stability of water ice

10.5194/epsc2020-96 ◽

2020 ◽

Author(s):

Hannah Susorney ◽

Carolyn Ernst ◽

Nancy Chabot

Keyword(s):

Polar Region ◽

Thermal Conditions ◽

Diameter Ratio ◽

Clear Correlation ◽

Polar Regions ◽

Thermal Models ◽

Water Ice ◽

The North ◽

North Polar ◽

Stability Of Water

Mercury&#8217;s polar regions host deposits of radar-bright material in regions of permanent shadow, commonly the interior of impact craters, and the deposits are hypothesised to be water ice (i.e., Chabot et al., 2018). Thermal modelling, prior to the arrival of the MESSENGER mission, found that water ice is not thermally stable in craters smaller than 10 km, assuming the craters had a depth-to-diameter ratio of 0.2 (Vasavada et al., 1999). Studies of the distribution of radar-bright deposits have identified deposits in craters under 10 km (Deutsch, et al., 2016). In this study, we used the high-resolution north polar topography from the MESSENGER mission to evaluate the morphometry and temperatures of craters with diameters of 5-10 km to explore if these craters could host stable water ice on geologic timescales. We measured the depth and diameter of 201 5-10 km in diameter craters between 75-85&#176; N. MLA tracks that bisected the crater were used to measure the depth and diameter of 99 craters, spanning all longitudes of this north polar region. Thermal models for the north polar region of Mercury use the gridded MLA topography sampled at 1 km resolution (Paige et al., 2013; Chabot et al., 2018), so it was important to ensure the gridded topography accurately captured the craters&#8217; shapes before using the results of these thermal models for these small craters, Comparisons between the MLA track profiles and the profiles taken through the gridded MLA product showed consistent depth to diameter profiles in both datasets, substantiating the use of the gridded MLA product to be used to determine depth and diameter values for these craters and the thermal models for these craters to be used to explore the stability of water ice in these craters. The average depth-to-diameter ratio of the 201 craters is 0.15, 25% lower than the estimate used in pre-MESSENGER thermal study (Vasavada et al., 1999). Thermal measurements of the 156 craters show that many of them have average temperatures below 110 K, meaning that they have thermal conditions that would allow water ice to be stable on geologic timescales under a thin layer of insulating material. Only three craters had small, single-pixel regions with maximum temperatures under 110 K, suggesting that water ice is not stable on the surface in the majority of small craters, except for isolated regions or below the 1-km scale of the thermal model. These results show that water ice would be stable in simple, sub-10 km diameter craters on Mercury and that the presence of radar-bright deposits in these craters is not a constraint on the age of radar-bright deposits. However, our mapping results do show a clear correlation with radar-bright signatures and longitude. In particular, around 60&#176;E longitude, we observe a higher percentage of radar-bright craters. One of Mercury&#8217;s two cold poles is nearby at 90&#176;E, but a large complex crater, Prokofiev-112 km in diameter, is also located at 64&#176;E and many of the craters that are radar-bright appear to be secondaries of Prokofiev. Possible explanations for this longitude distribution are being actively investigated, including association with Prokofiev, cold-pole thermal conditions, effects of radar visibility, and the potential for uneven water ice distribution in the small craters near Mercury&#8217;s north pole. &#160;

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Avalanches of the martian north polar cap

10.5194/egusphere-egu2020-22331 ◽

2020 ◽

Author(s):

Patricio Becerra ◽

Susan Conway ◽

Nicholas Thomas ◽

Keyword(s):

Polar Regions ◽

Martian Surface ◽

Polar Cap ◽

Water Ice ◽

The North ◽

Imaging Science ◽

Resolution Imaging ◽

North Polar ◽

Gas Expansion ◽

Trigger Mechanisms

In 2008, the High Resolution Imaging Science Experiment (HiRISE) on board NASA&#8217;s MRO fortuitously captured several discrete clouds of material in the process of cascading down a steep scarp of the water-ice-rich north polar layered deposits (NPLD). The events were only seen during a period of ~4 weeks, near the onset of martian northern spring in 2008, when the seasonal cover of CO2 is beginning to sublimate from the north polar regions. Russell et al. [1] analyzed the morphology of the clouds, inferring that the particles involved were mechanically analogous to terrestrial &#8220;dry, loose snow or dust&#8221;, so that the events were similar to terrestrial &#8220;powder avalanches&#8221; [2]. HiRISE confirmed the seasonality of avalanche occurrence the following spring, and continued to capture between 30 and 50 avalanches per season (fig. 1b,c) between 2008 and 2019, for a total of 7 Mars Years (MY29&#8211;MY35) of continuous scarp monitoring.In this work we will present statistics on these events, in an attempt to quantify their effect on the mass balance of the NPLD, and with respect to competing processes such as viscous deformation and stress-induced block falls that do not trigger avalanches [3,4]. We also use a 1D thermal model [5] to investigate the sources and trigger mechanisms of these events. The model tracks the accumulation and ablation of seasonal CO2 frost on a martian surface. Russell et al. [1] support an initiation through gas-expansion related to the presence of CO2 frost on the scarp. Therefore the amount of frost that lingers on different sections of the model scarp at the observed time of the avalanches will provide evidence either for or against this particular mechanism. We will present preliminary results and discuss their implications.References: [1] P. Russell et al. (2008) Geophys. Res. Lett. 35, L23204. [2] D. McClung, P.A. Schaerer (2006), Mountaineers, Seattle Wash. [3] Sori, M. M., et al., Geophys. Res. Lett., 43. [4] Byrne et al. (2016), 6th Int. Conf. Mars Polar Sci. Exploration [4] C. M. Dundas and S. Byrne (2010) Icarus 206, 716.

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