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  • 1
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    Sunspot Group Decay (2008)
    Springer
    Details
    Publication Date: 2008-07-14
    Print ISSN: 0038-0938
    Electronic ISSN: 1573-093X
    Topics: Physics
    Published by Springer
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  • 2
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    Solar Cycle Forecasting (2008)
    Springer
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    Publication Date: 2008-09-16
    Print ISSN: 0038-6308
    Electronic ISSN: 1572-9672
    Topics: Physics
    Published by Springer
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  • 3
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    Geomagnetic activity indicates large amplitude for sunspot cycle 24 (2006)
    American Geophysical Union
    Details
    Publication Date: 2006-09-01
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by American Geophysical Union
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  • 4
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    Solar Rossby Wave 'Hills' Identified As Supergranules (2007)
    In:  CASI
    Details
    Publication Date: 2018-06-12
    Description: We explore the nature of 'hills' observed on the solar surface which had previously been attributed to Rossby waves. We investigate the sol ar hills phenomenon by analyzing the output from a synthetic model ba sed solely on the observed solar photospheric convection spectrum. We show that the characteristics of these hills can be explained by the corrugation of the surface produced by the radial flows of the conve ction. The hills in our simulations are dominated by supergranules, a well-known component of solar convection. Rossby waves have been predicted to exist within the Sun and may play an important role in the d ynamics of the solar interior, including the Sun's differential rotat ion and magnetic dynamo. Our study suggests, however, that the hills observed at the solar limb do not confirm the existence of solar Ross by waves.
    Keywords: Solar Physics
    Format: application/pdf
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  • 5
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    The Art and Science of Long-Range Space Weather Forecasting (2006)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: Long-range space weather forecasts are akin to seasonal forecasts of terrestrial weather. We don t expect to forecast individual events but we do hope to forecast the underlying level of activity important for satellite operations and mission pl&g. Forecasting space weather conditions years or decades into the future has traditionally been based on empirical models of the solar cycle. Models for the shape of the cycle as a function of its amplitude become reliable once the amplitude is well determined - usually two to three years after minimum. Forecasting the amplitude of a cycle well before that time has been more of an art than a science - usually based on cycle statistics and trends. Recent developments in dynamo theory -the theory explaining the generation of the Sun s magnetic field and the solar activity cycle - have now produced models with predictive capabilities. Testing these models with historical sunspot cycle data indicates that these predictions may be highly reliable one, or even two, cycles into the future.
    Keywords: Space Sciences (General)
    Type: Space Weather Week: The Meeting of Science, Research, Applications, Operation, and Users; Apr 25, 2006 - Apr 28, 2006; Boulder, CO; United States
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  • 6
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    Predicting the Sunspot Cycle (2009)
    In:  Other Sources
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    Publication Date: 2019-07-19
    Description: The 11-year sunspot cycle was discovered by an amateur astronomer in 1844. Visual and photographic observations of sunspots have been made by both amateurs and professionals over the last 400 years. These observations provide key statistical information about the sunspot cycle that do allow for predictions of future activity. However, sunspots and the sunspot cycle are magnetic in nature. For the last 100 years these magnetic measurements have been acquired and used exclusively by professional astronomers to gain new information about the nature of the solar activity cycle. Recently, magnetic dynamo models have evolved to the stage where they can assimilate past data and provide predictions. With the advent of the Internet and open data policies, amateurs now have equal access to the same data used by professionals and equal opportunities to contribute (but, alas, without pay). This talk will describe some of the more useful prediction techniques and reveal what they say about the intensity of the upcoming sunspot cycle.
    Keywords: Solar Physics
    Type: M09-0258 , European AstroFest 2009; Jan 06, 2009 - Jan 07, 2009; London; United Kingdom
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  • 7
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    Meridional Flow Variations Over Three Solar Cycles - What Happened in Cycle 23? (2009)
    In:  Other Sources
    Details
    Publication Date: 2019-07-19
    Description: The meridional flow speed determines the strength of the Sun s polar fields in both surface flux transport models and in flux transport dynamos. The polar fields produced during cycle 23 were half as strong as those produced in the previous two cycles. Helioseismic measurements of the meridional flow over the rising phase of cycle 23 indicated a decrease in flow velocity. This observation was used in flux transport dynamo models to predict a delayed start for cycle 24 and was consistent with weak polar fields and a slower equatorward drift of the active latitudes during cycle 23. On the other hand, the surface flux transport models require a faster meridional flow to produce the weak polar fields. We have begun measurements of the surface meridional flow by tracking the motions of weak (outside active regions) magnetic field elements in magnetograms from SOHO/MDI over cycle 23 and from NSO/Kitt Peak over cycles 21 to 23. We confirm the slowdown of the meridional flow over the rising phase of cycle 23 but find that the flow speed returned to its previous level during the declining phase of cycle 23. Furthermore, this appears to be a normal feature of the meridional flow during sunspot cycles. The flow is fast at minima and slow at maxima. The lack of a significantly different meridional flow during cycle 23 is very problematic for both surface flux transport models and flux transport dynamos.
    Keywords: Solar Physics
    Type: M09-0410 , American Astronomical Society/Solar Physics Division Meeting (AAS/SPD); Jun 14, 2009 - Jun 19, 2009; Boulder, CO; United States
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  • 8
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    Geomagnetic Activity Indicates Large Amplitude for Sunspot Cycle 24 (2006)
    In:  Other Sources
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    Publication Date: 2019-07-19
    Description: The level of geomagnetic activity near the time of solar activity minimum has been shown to be a reliable indicator for the amplitude of the following solar activity maximum. The geomagnetic activity index aa can be split into two components: one associated with solar flares, prominence eruptions, and coronal mass ejections which follows the solar activity cycle and a second component associated with recurrent high speed solar wind streams which is out of phase with the solar activity cycle. This second component often peaks before solar activity minimum and has been one of the most reliable indicators for the amplitude of the following maximum. The size of the recent maximum in this second component indicates that solar activity cycle 24 will be much higher than average - similar in size to cycles 21 and 22 with a peak smoothed sunspot number of 160 plus or minus 25.
    Keywords: Geophysics
    Type: 2006 AGU Fall Meeting; Dec 11, 2006 - Dec 14, 2006; San Francisco, CA; United States
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  • 9
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    Decay of Solar Active Regions (2005)
    In:  Other Sources
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    Publication Date: 2019-07-18
    Description: We examine the record of sunspot group areas observed over a period of 100 years to determine the rate of decay of solar active regions. We exclude observations of groups when they are more than 60deg in longitude from the central meridian and only include data when at least three days of observations are available following the date of maximum area for a spot group's disk passage. This leaves data for some 24,000 observations of active region decay. We find that the decay rate is a constant 20 microHem/day for spots smaller than about 200 microHem (about the size of a supergranule). This decay rate increases linearly to about 90 microHem/day for spots with areas of 1000 microHem. We find no evidence for significant variations in active region decay from one solar cycle to another. However, we do find that the decay rate is slower at lower latitudes. This gives a slower decay rate during the declining phase of sunspot cycles.
    Keywords: Solar Physics
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  • 10
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    The Supergranule Super-Rotation Illusion (2006)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: Peculiar aspects of the rotation rate of the supergranules have been noted for over 20 years now. This has culminated in recent reports suggesting that the supergranules have wave-like characteristics and propagate prograde at a rate that exceeds that of the plasma anywhere below the surface. We have simulated supergranules that rotate at a rate that is independent of position or size and find that they appear to rotate at a more rapid rate. This super-rotation of the supergranules is seen in both cross-correlation and Fourier analyses of the Doppler velocity pattern. The amplitude of the rotation excess as a function of-size matches that seen in the Fourier analyses of MDI data. The source of this rotation excess is identified with the effect of projecting velocity signals into the line-of-sight. We conclude that supergranules are merely advected by the flow in the near-surface shear layer and that their apparent super-rotation does not indicate wave-like properties.
    Keywords: Plasma Physics
    Type: American Astronomical Society, Solar Physics Division, Conference; Jun 25, 2006 - Jun 30, 2006; Durham, NH; United States
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