solar cycle

On the connection between Rieger-type and magneto-Rossby waves driving the frequency of the large solar eruptions during Solar Cycles 19 - 25

whawkins — Thu, 19 Jan 2023 22:39:58 +0000

On the connection between Rieger-type and magneto-Rossby waves driving the frequency of the large solar eruptions during Solar Cycles 19 - 25 whawkins Thu, 01/19/2023 - 15:39

Author:

whawkins

Jan 19, 2023

The black curve is the monthly mean total sunspot number from the beginning of SC23 until 2022 May. The red vertical line represents the major flare activity period of SC23, SC24, and SC25. The blue/green vertical line refers to the identified periods of the magneto-Rossby waves in the longitudinal/latitudinal movement of the global magnetic field during SC23-24. The blue/green vertical dashed line refers to identified periods of Rieger-type in the longitudinal/latitudinal movement of the global magnetic field during SC23-24. The short magenta/orange vertical dashed line refers to the elapsed time of the >100-day period in the longitudinal/latitudinal movement before the first X-class flare occurred in each solar cycle.

Astrophysical Journal: Global solar activity variation mainly occurs over about an 11-year cycle. However, both longer and shorter periodicities than the solar cycle are also present in many different solar activity indices. The longer timescales may be up to hundreds of years, while the shorter timescales for global solar variability could be within 0.5 - 2 years, which include e.g. from the Rieger-type periods (150–160 days) to QBOs (quasi-biennial oscillations) of 2 years. The most likely origin of this short-timescale quasi-periodicity is attributed to magnetic Rossby waves, which have periods of 0.8—2.4 years. In this work, we present findings of a unique evolution of identified shorter periodicities, like the Rieger-type, arising from magnetic Rossby waves, throughout the Solar Cycles 19-25. We report further observational evidence of the strong relationship between the Rieger-type periodicity, magneto-Rossby waves, and major solar flare activity. Moreover, this study also reveals that the global solar magnetic field has a continuous periodic longitudinal conveyor belt motion along the solar equator together with an up-and-down movement in the latitudinal directions. We found that when these longitudinal and latitudinal movements have Rieger-type periodicity and magneto-Rossby waves during the same period of a solar cycle then major flare activity is present.

Magnetohydrodynamics Instabilities of Double Magnetic Bands in a Shallow-water Tachocline Model: I Cross-equatorial Interactions of Bands

whawkins — Thu, 19 Jan 2023 22:16:14 +0000

Magnetohydrodynamics Instabilities of Double Magnetic Bands in a Shallow-water Tachocline Model: I Cross-equatorial Interactions of Bands whawkins Thu, 01/19/2023 - 15:16

Author:

whawkins

Jan 19, 2023

For low effectiive gravity (G = 0.5) growth rate contours for m = 1 modes are displayed in the field-strength space, in which x-axis denotes the strength of the high-latitude band and the y-axis that of the low-latitude band. Left and right panels are respectively for antisymmetric (m = 1,A) and symmetric (m = 1,S) modes. As the band-system migrates from high latitudes towards the equator, four rows from top to the bottom show how the instability features change respectively for bands at 60◦ − 30◦ (aa,ab), 50◦ − 20◦ (ba,bb), 40◦ − 10◦ (ca,cb) and 35◦ − 5◦.

Astrophysical Journal: Along with the ”butterfly diagram” of sunspots, combined observational studies of ephemeral active regions, X-ray and EUV brightpoints, plage, filaments, faculae and prominences demonstrate a pattern, which is known as the Extended Solar Cycle (ESC). This pattern indicates the wings of the sunspot butterfly could be extended to much higher latitudes (up to ∼ 60 degrees), to earlier time than the start of a sunspot cycle, hence yielding a strong overlap between cycles. Thus during the ongoing cycle’s activity near 30-degrees latitude in each hemisphere, the next cycle kicks off at around 60- degrees. By representing these epochs of overlaps by oppositely-directed double magnetic bands in each hemisphere, we compute the unstable eigenmodes for MHD Rossby waves at the base of the convection zone and study how the properties of these energetically active Rossby waves change as these band-pairs migrate equatorward. We find that in each hemisphere the low-latitude band interacts with the high-latitude band and drive the MHD instability as the solar activity progresses from 35◦ to 15◦ latitude, which is essentially the rising phase. When the activity proceeds further equatorward from 15-degrees, interaction between low- and high-latitude bands weakens, and the cross-equatorial interaction between two low-latitude bands in each hemisphere starts. The eigenmodes in latitude- longitude planforms also reflect such changes in their pattern as the bend of the the active cycle moves below 15-degree latitude.

Study of Coronal Hole Lifetimes

whawkins — Wed, 31 Aug 2022 20:29:27 +0000

Study of Coronal Hole Lifetimes whawkins Wed, 08/31/2022 - 14:29

Author:

whawkins

Aug 31, 2022

Coronal hole centroid latitude vs. Carrington Rotation (bottom) and year (top) for almost three solar cycles (SC21-23). Red represents negative polarity and blue represents positive polarity, with the darker shades representing longer lifetimes, i.e., the number of rotations a given coronal hole or grouping of coronal holes recurs (assuming a rigid 27.3 day rotation rate). Note that coronal holes that last for more than one rotation are plotted for each rotation at the location of their centroid position for that rotation. The 11-year magnetic polarity change at the poles as seen with coronal holes is clear as is the slight asymmetry of the evolution of coronal holes at each pole – i.e., the new polarity coronal hole appears at the north poleslightly before the south pole. The beginning of the solar cycles are marked with a vertical dashed line and based on Sunspot Index and Long-term Solar Observations (SILSO) sunspot numbers.

Version 2; SILSO data available from Royal Observatory of Belgium, Brussels

Ian Hewins, Sarah Gibson, David Webb, Bob McFadden, Thomas Kuchar, and Barbara Emery-Geiger

Using the McIntosh Archive of solar features, we analyze the evolution of coronal holes over more than three solar cycles. We demonstrate that coronal hole positions and lifetimes change dramatically on time scales from months to yrs, and that the pattern of these changes is clearly linked to the solar activity cycle. We demonstrate that the lifetimes of low-latitude coronal holes are usually less than one rotation but may extend to as long as three years. When plotted over time, the positions of low latitude coronal holes that remain visible for over one rotation track the sunspot butterfly diagram in terms of their positions on the sun over a solar cycle. Finally, we confirm that coronal holes do not in general rigidly rotate.

Annie Maunder, A Pioneer of Solar Astronomy

kolinski — Thu, 18 Nov 2021 22:11:08 +0000

Annie Maunder, A Pioneer of Solar Astronomy kolinski Thu, 11/18/2021 - 15:11

Author:

kolinski

Nov 18, 2021

If you have visited the High Altitude Observatory (HAO) at NCAR in Boulder, CO, you may recall seeing the Maunder’s original butterfly diagram. The chart resembles three butterflies traveling west. Drawn by Annie S.D. Maunder and E. Walter Maunder, it demonstrated for the first time the movement of sunspot emergence from the poles toward the equator over the sun's 11-year cycle. In October of 2016, the Royal Observatory at Greenwich remembered Annie Maunder as one of the first women elected as a RAS Fellows: the A & G Forum (News, Views, and Events from the RAS Fellows) stated that "Annie Maunder was finally elected to RAS Fellowship in 1916."

A pioneer of solar astronomy

Annie Maunder

Annie was an outstanding observer and interpreter of sun activity. She was born Annie Scott Dill Russell in 1868 in Strabane, in what is now Northern Ireland. Although she was unusually well-educated for a women for her time and she had passed the Cambridge University degree examinations with honors in mathematics (1889), she was not allowed to receive a degree. Annie had the foresight to mail her butterfly diagram from London to the US, for protection, during the English Blitz. In 1946 it was gifted to Walter Orr Roberts where it remains on permanent display at HAO.

An excerpt from the a 2000 interview with Tom Bogden shares that Annie Maunder explained: "We made this diagram in a week of evenings, one dictating and the other ruling these little lines. We had to do it in a hurry because we wanted to get it before the [Royal Astronomical] Society at the same meeting as the other sunspot observers, whose views we knew to be heretical. As it turned out the diagram wiped [the other observers'] papers clean off the slate."

Maunder Diagram from 1940 by Annie Maunder and her husband Walt.

Annie worked with Walter Maunder at the solar department of the Greenwich Royal Observatory in England as a "lady computer" from 1891 until they married in 1895. Although Annie was required to resign when she married her boss, the two continued to collaborate on their own. Annie accompanied her husband on eclipse expeditions and developed a camera for photographing the corona.

Great Grandson of Walter & Annie Maunder Thanks HAO

kolinski — Thu, 18 Nov 2021 21:13:24 +0000

Great Grandson of Walter & Annie Maunder Thanks HAO kolinski Thu, 11/18/2021 - 14:13

Author:

kolinski

Nov 18, 2021

Andrew L Maunder wrote HAO: I just wanted to drop you an email to thank you for the recent bio pages for Walter and Annie S D Maunder presented on the UCAR NCAR website. In particular, I’m pleased to see the Elliot and Fry studio portrait being used for Annie. For so long there were no good images of her in the public domain, and so I have been very pleased to get this one out there for all to see.

I am a great grandson of Walter Maunder, and live over here in the USA in North Carolina. From the snapshots below you will see that I’m lucky enough to still have a few of their possessions (Walter’s New testament, and Annie’s birthday book).

Perhaps if my wife and I are ever able to make it out to Boulder, we may be able to visit and see the famous butterfly diagram?

Regards,
Andrew L Maunder

Annie Maunder's birthday book and her formal portrait.

Walter Maunder’s New testament with his formal portrait.

Thermal Properties of Coronal Cavities

kolinski — Thu, 18 Nov 2021 17:29:30 +0000

Thermal Properties of Coronal Cavities kolinski Thu, 11/18/2021 - 10:29

Publication Name: Astronomy and Astrophysics; First HAO Author's Name: Sarah Gibson

Author:

kolinski

Nov 18, 2021

We have analyzed 33 cavities observed between 2012 and 2018, from solar activity maximum to minimum. For each cavity we applied a differential emission measure method to obtain both a temperature distribution and a value of the average temperature.

Average temperature of 35 cavities (black) and their surrounding streamers (red).

We find that cavities are filled with material hotter than the surrounding streamer, with temperatures in the range of 1.67 - 2.15 MK. Differences between temperatures of cavities and surrounding streamers are in the range of 0.11 - 0.32 MK with an average value of 0.21 MK. We found that temperatures of both, cavities and streamers, vary as a function of different phases of solar activity. During solar maximum the structures are slightly hotter than those observed during solar minimum (1.85 - 2.15 MK vs. 1.67 - 1.88 MK for cavities and streamers, respectively).

Link to paper: Thermal Properties of Coronal Cavities

solar cycle

On the connection between Rieger-type and magneto-Rossby waves driving the frequency of the large solar eruptions during Solar Cycles 19 - 25

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