Solar radio and extreme UV during current cycle

Posted: August 6, 2016 by tchannon in Solar physics

Tim wrote,

From A& A (Astronomy and Astrophysics) this month is a paper where some readers will take a shine.


Comparison of solar radio and extreme ultraviolet synoptic limb charts during the present solar maximum
A. J. Oliveira e Silva, C. L. Selhorst, P. J. A. Simões and C. G. Giménez de Castro
A&A, 592 (2016) A91
(free access with registration)

Aims. The present solar cycle is particular in many aspects: it had a delayed rising phase, it is the weakest of the last 100 yrs, and it presents two peaks separated by more than one year. To understand the impact of these characteristics on the solar chromosphere and coronal dynamics, images from a wide wavelength range are needed. In this work we use the 17 GHz radio continuum, which is formed in the upper chromosphere and the extreme ultraviolet (EUV) lines 304 and 171 Å, that come from the transition region (He ii , T ~ 6-8 × 10 4 K) and the corona (Fe IX, X, T ~ 10 6 K), respectively. We extend upon a previous similar analysis, and compare the mean equatorial and polar brightening behavior at radio and EUV wavelengths during the maximum of the present solar cycle, covering the period between 2010 and 2015.
Methods. We analyze daily images at 304 and 171 Å obtained by the atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). The 17 GHz maps were obtained by the Nobeyama Radioheliograph (NoRH). To construct synoptic limb charts, we calculated the mean emission of delimited limb areas with 100 00 wide and angular separation of 5 ? .
Results. At the equatorial region, the results show a hemispheric asymmetry of the solar activity. The northern hemisphere dominance is coincident with the first sunspot number peak, whereas the second peak occurs concurrently with the increase in the activity at the south. The polar emission reflects the presence of coronal holes at both EUV wavelengths, moreover, the 17 GHz polar brightenings
can be associated with the coronal holes. Until 2013, both EUV coronal holes and radio polar brightenings were more predominant at the south pole. Since then they have not been apparent in the north, but thus appear in the beginning of 2015 in the south as observed in the synoptic charts.
Conclusions. This work strengthens the association between coronal holes and the 17 GHz polar brightenings as it is evident in the synoptic limb charts in agreement with previous case study papers. The enhancement of the radio brightness in coronal holes is explained by the presence of bright patches closely associated with the presence of intense unipolar magnetic fields. However, observations with better spatial resolution and also at different radio wavelengths will be necessary to fully understand the physical mechanisms that link these features.

From the main article Discussions and Conclusions I’ve extracted something I find intersting, YMMV. For me the invisible magnetic properties of the sun are more important than the visible, magnetic is the primary. Moreover any mention of polar / hemisphere asymmetry is worthy of investigation since here lie terrestrial correlations. Quite why, the mechanism, is unclear.

5.1. Equatorial region
At the equatorial region, the results for the three wavelengths clearly show the hemispheric asymmetry in the solar activity (see for example: Hathaway 2010). The dominance of the northern hemisphere coincided with the first SSN peak, whereas the second SSN peak occurs simultaneously with increase in the activity at the south (see Fig. 4). There is an interval between the peaks (around the beginning of 2013), which indicates an inversion in the asymmetry of the hemispheric activity. Moreover, the comparison between the hemispheres shows that the peak of activity in the south is more intense for all three wavelengths.
The stronger southern activity started in the first semester of 2013 and is coincident with the complete polar field reversion of the north pole (Mordvinov et al. 2015). Since solar cycle 20, polar field reversals first occurred in the north (Svalgaard & Kamide 2013), all those cycles showed a more intense first peak. This trend has clearly changed in the present cycle, being the more intense the second peak.
The monthly equatorial radio hI R i in both hemispheres presented an overall positive correlation with the EUV (see Table1).
The trend has clearly changed in the present cycle, in which the second peak is more intense. A stronger activity in the southern hemisphere was more noticeable at 17 GHz and 304 Å, which both formed in the lower atmosphere.

Post by Tim

  1. oldbrew says:

    ‘the presence of intense unipolar magnetic fields’

    Meaning not clear – unipolar magnets don’t exist. All magnets are bipolar.

  2. tchannon says:

    The fabled monopole. Mind you I’m not sure I want one. |:-) would probably be munitions.

    What the authors mean, good question. Their first language is not English. I assume they mean strong one way, return circuit not stated. What do I know though.

  3. Geoff Sharp says:

    I think the unipolar reference is related to the coronal holes. Unipolar sunspot regions can also occur with single spot groups but suspect in this case to be not what the authors are referring to.

  4. oldbrew says:

    ‘The mysterious missing magnetic monopole’

    Still missing: ‘The Monopole and Exotics Detector at the Large Hadron Collider (MoEDAL) has taken up the search, but has found no monopoles to date.’

  5. p.g.sharrow says:

    Tough to find something that doesn’t exist except in the fevered brain of a theorist. While Mathematicians can create wondrous things in their formula to explain things they don’t understand. GOD is not a mathematician! GOD works in Applied Science, You know, Engineering stuff that HAS to work…pg