Low-Latitude Coronal Holes at the Minimum of the 23rd Solar Cycle

Abstract

Low and mid-latitude coronal holes (CHs) observed on the Sun during the current solar activity minimum (from September 21, 2006, Carrington rotation (CR) 2048, until June 26, 2009 (CR 2084)) were analyzed using {\it SOHO}/EIT and STEREO-A SECCHI EUVI data. From both the observations and Potential Field Source Surface (PFSS) modeling, we find that the area occupied by CHs inside a belt of $\pm 40^{\circ }$ around the solar equator is larger in the current 2007 solar minimum relative to the similar phase of the previous 1996 solar minimum. The enhanced CH area is related to a recurrent appearance of five persistent CHs, which survived during 7-27 solar rotations. Three of the CHs are of positive magnetic polarity and two are negative. The most long-lived CH was being formed during 2 days and existed for 27 rotations. This CH was associated with fast solar wind at 1 AU of approximately 620$\pm 40$ km s${}^{-1}$. The 3D MHD modeling for this time period shows an open field structure above this CH. We conclude that the global magnetic field of the Sun possessed a multi-pole structure during this time period. Calculation of the harmonic power spectrum of the solar magnetic field demonstrates a greater prevalence of multi-pole components over the dipole component in the 2007 solar minimum compared to the 1996 solar minimum. The unusual large separation between the dipole and multi-pole components is due to the very low magnitude of the dipole component, which is three times lower than that in the previous 1996 solar minimum.

14 pages, 7 figures

References in corpus (1)

• Parameters of the Magnetic Flux inside Coronal Holes

Cited by in corpus (15)

• The Open Flux Problem
• Three-dimensional Evolution of Solar Wind during Solar Cycles 22-24
• Time Distributions of Large and Small Sunspot Groups Over Four Solar Cycles
• On the origin of two X-class flares in active region NOAA 12673 - Shear flows and head-on collision of new and pre-existing flux
• A Comparison Between Global Proxies of the Sun's Magnetic Activity Cycle: Inferences from Helioseismology
• On the 27-day Variations of Cosmic Ray Intensity in Recent Solar Minimum 23/24
• Maximum Coronal Mass Ejection Speed as an Indicator of Solar and Geomagnetic Activities
• Modeling the Solar Wind at the Ulysses, Voyager, and New Horizons Spacecraft
• Study of the 27-day variations in GCR fluxes during 2007-2008 based on PAMELA and ARINA observations
• Sources of The Slow Solar wind During the Solar Cycle 23/24 Minimum
• Critical frequencies of the ionospheric $F_1$ and $F_2$ layers during the last four solar cycles: sunspot group type dependencies
• Coronal electron density, temperature and solar spectral irradiance during the solar cycle 23 and 24
• Is Solar Minimum 24/25 Another Unusual One?
• Temporal Offsets between Maximum CME Speed Index and Solar, Geomagnetic, and Interplanetary Indicators during Solar Cycle 23 and the Ascending Phase of Cycle 24
• SIP-IFVM: Efficient time-accurate magnetohydrodynamic model of the corona and coronal mass ejections