Solar cycle 24

About: Solar cycle 24 is a research topic. Over the lifetime, 861 publications have been published within this topic receiving 14845 citations.

Sunspot cycle 24 : Smallest cycle in 100 years?

Abstract: : Predicting the peak amplitude of the sunspot cycle is a key goal of solar-terrestrial physics. The precursor method currently favored for such predictions is based on the dynamo model in which large-scale polar fields on the decline of the 11-year solar cycle are converted to toroidal (sunspot) fields during the subsequent cycle. The strength of the polar fields during the decay of one cycle is assumed to be an indicator of peak sunspot activity for the following cycle. Polar fields reach their peak amplitude several years after sunspot maximum; the time of peak strength is signaled by the onset of a strong annual modulation of polar fields due to the 7 1/4-degree tilt of the solar equator to the ecliptic plane. Using direct polar field measurements, now available for four solar cycles, the authors predict that the approaching solar cycle 24 (approx. 2011 maximum) will have a peak smoothed monthly sunspot number of 75 +/- 8, making it potentially the smallest cycle in the last 100 years.

Predicting Solar Cycle 24 With a Solar Dynamo Model

Abstract: Whether or not the upcoming cycle 24 of solar activity will be strong is being hotly debated. The solar cycle is produced by a complex dynamo mechanism. We model the last few solar cycles by “feeding‿ observational data of the Sun's polar magnetic field into our solar dynamo model. Our results fit the observed sunspot numbers of cycles 21–23 reasonably well and predict that cycle 24 will be about 35% weaker than cycle 23.

Predicting the strength of solar cycle 24 using a flux-transport dynamo-based tool

Abstract: [1] We construct a solar cycle strength prediction tool by modifying a calibrated flux-transport dynamo model, and make predictions of the amplitude of upcoming solar cycle 24. We predict that cycle 24 will have a 30–50% higher peak than cycle 23, in contrast to recent predictions by Svalgaard et al. and Schatten, who used a precursor method to forecast that cycle 24 will be considerably smaller than 23. The skill of our approach is supported by the flux transport dynamo model's ability to correctly 'forecast' the relative peaks of cycles 16–23 using sunspot area data from previous cycles.

Evolution of Magnetic Field and Energy in A Major Eruptive Active Region Based on SDO/HMI Observation

Abstract: We report the evolution of magnetic field and its energy in NOAA active region 11158 over 5 days based on a vector magnetogram series from the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamic Observatory (SDO). Fast flux emergence and strong shearing motion led to a quadrupolar sunspot complex that produced several major eruptions, including the first X-class flare of Solar Cycle 24. Extrapolated non-linear force-free coronal fields show substantial electric current and free energy increase during early flux emergence near a low-lying sigmoidal filament with sheared kilogauss field in the filament channel. The computed magnetic free energy reaches a maximum of ∼2.6 × 10 32 erg, about 50% of which is stored below 6 Mm. It decreases by ∼0.3 × 10 32 erg within 1 hour of the X-class flare, which is likely an underestimation of the actual energy loss. During the flare, the photospheric field changed rapidly: horizontal field was enhanced by 28% in the core region, becoming more inclined and more parallel to the polarity inversion line. Such change is consistent with the conjectured coronal field “implosion”, and is supported by the coronal loop retraction observed by the Atmospheric Imaging Assembly (AIA). The extrapolated field becomes more “compact” after the flare, with shorter loops in the core region, probably because of reconnection. The coronal field becomes slightly more sheared in the lowest layer, relaxes faster with height, and is overall less energetic.

> 25 MeV Proton Events Observed by the High Energy Telescopes on the STEREO A and B Spacecraft and/or at Earth During the First ∼ Seven Years of the STEREO Mission

Abstract: Using observations from the High Energy Telescopes (HETs) on the STEREO A and B spacecraft and similar observations from near-Earth spacecraft, we summarize the properties of more than 200 individual > 25 MeV solar proton events, some detected by multiple spacecraft, that occurred from the beginning of the STEREO mission in October 2006 to December 2013, and provide a catalog of these events and their solar sources and associations. Longitudinal dependencies of the electron and proton peak intensities and delays to onset and peak intensity relative to the solar event have been examined for 25 three-spacecraft particle events. Expressed as Gaussians, peak intensities fall off with longitude with σ=47±14∘ for 0.7 – 4 MeV electrons, and σ=43±13∘ for 14 – 24 MeV protons. Several particle events are discussed in more detail, including one on 3 November 2011, in which ∼ 25 MeV protons filled the inner heliosphere within 90 minutes of the solar event, and another on 7 March 2012, in which we demonstrate that the first of two coronal mass ejections that erupted from an active region within ∼ 1 hour was associated with particle acceleration. Comparing the current Solar Cycle 24 with the previous cycle, the first > 25 MeV proton event was detected at Earth in the current solar cycle around one year after smoothed sunspot minimum, compared with a delay of only two months in Cycle 23. Otherwise, solar energetic particle event occurrence rates were reasonably similar during the rising phases of Cycles 23 and 24. However, the rate declined in 2013, reflecting the decline in sunspot number since the peak in the northern-hemisphere sunspot number in November 2011. Observations in late 2013 suggest that the rate may be rising again in association with an increase in the southern sunspot number.