Update on Cycle 24 Giuliana de Toma collaborators: Gary Chapman, Angie Cookson, Dora Preminger data sources: CSUN/SFO, USAF/SOON, McMath, SOHO/MDI, SDO/AIA SPD 2013 Press Conference
Solar Cycle 24 is different from recent cycles follows longest/deepest minimum in 100 years weakest cycle of the space age interesting N/S asymmetry (also seen at the poles) SDO/HMI Magnetogram Mar USAF/NOAA data cycle 22cycle 21
north/south asymmetry started in 2005 current spot latitude N = 14deg S = -18deg ~ 2-year time lag The two hemispheres have been out of phase for an unusually long time South activity has increased recently The differences started in the cycle 23 USAF/NOAA data
significant decrease of very large spots in cycle 23 The differences started in cycle 23 ~1400 SDO/AIA May
significant decrease of very large spots in cycle 23 The differences started in cycle 23 spots of all sizes have decreased in cycle 24, especially the large ones ~1400 AIA May
Hevelius drawing in 1644 (one year before the Maunder Minimum started) There were large spots on the Sun before the Maunder Minimum We still do not know how and why the Maunder Minimum started We had small cycles before and the Sun did not go into a Maunder Minimum
Sunspots are not fainter spots have the expected brightness for a given area SFO/CFDT present longest record of full-disk photometric measurements sunspots are not fainter there are just fewer of them… …which is normal for weak cycles this is why weak cycles are weak! San Fernando Observatory/CFDT1 cycle 22 cycle 23
McMath-Pierce spot observations….. …. a lively debate Courtesy of L. Svalgaard brightness increase magnetic field decline if trend continues almost no spots in cycle 25 !! Livingston, Penn, & Svalgaard 2012 but is this trend real? spot brightness magnetic field
McMath-Pierce spot observations….. …. a lively debate brightness increase magnetic field decline spot brightness CFDT1 San Fernando Observatory/CFDT1 San Fernando Observatory/CFDT2 SOHO/MDI find spot brightness stable in time
another explanation for this trend McMath-Pierce dataset is not homogeneous - fewer data early on - no small spots included in early data this introduces a bias no trend in the most recent data that do not include small spots spot brightness magnetic field
another explanation for this trend McMath-Pierce dataset is not homogeneous - fewer data early on - no small spots included in early data this introduces a bias no trend in recent data that include small spots spot brightness CFDT1: all spots
another explanation for this trend McMath-Pierce dataset is not homogeneous - fewer data early on - no small spots included in early data this introduces a bias The trend is not caused by a real change in the Sun but by selection effects spot brightness CFDT1: with small spots removed in early years
There is one instrument that can resolve the ongoing controversy: MLSO/PSPT 1” spatial resolution 0.1% photometric precision 1998-present most accurate record of spots and faculae Collaboration with Gary Chapman (CSUN/SFO) & Mark Rast (CU/LASP) Stay tuned for more news on this! Blue cont nm Mauna Loa Solar Observatory
McMP restored image 0.2” AIA full res 0.6” AIA reduced to 2.4” CFDT1 5.0” AIA Aug CFDT1 low spatial resolution but 1% photometric precision
M. Rempel (ApJ Lett 2012) proposed the non-appearance of the high-latitude branch was be due to a change in the differential rotation profile (caused by the decrease in cycle amplitude) Strong cycles have more rigid differential rotation (magnetic tension tends to reduce rotation shear) Weak cycles rotate more differentially, i.e. poles slow down If a mean differential rotation profile is subtracted the polarward branch is hidden If 3.5-year rotational Mean is subtracted polarward branch reappears! R. Howe et al. (ApJ 2013)