30 research outputs found
Variation of small scale magnetic fields over a century using Ca-K images as proxy
A combined uniform and long-time series of Ca-K images from the Kodaikanal
Observatory (KO), Mount Wilson Observatory (MWO), and Mauna Loa Solar
Observatory (MLSO) were used to identify and study the Ca-K small-scale
features and their solar cycle variations over a century. The small scale
features are classified into three distinct categories: enhanced network (EN),
active network (AN), and quiet network (QN). All these features show that their
areas vary according to the 11-year solar cycle. The relative amplitude of the
Ca-K network variations agree with that of the sunspot cycle. The total area of
these small-scale features varies from about 5% during the minimum phase of the
solar cycle to about 20% during its maximum phase. Considering the average
intensity and the amplitude of their area variations, we find that the total
contribution of EN, AN and QN to the irradiance variation of the Sun is about
3%.Comment: Submitted article in RAA. It is under review. 15 pages, 8 figure
On a limitation of Zeeman polarimetry and imperfect instrumentation in representing solar magnetic fields with weaker polarization signal
Full disk vector magnetic fields are used widely for developing better
understanding of large-scale structure, morphology, and patterns of the solar
magnetic field. The data are also important for modeling various solar
phenomena. However, observations of vector magnetic fields have one important
limitation that may affect the determination of the true magnetic field
orientation. This limitation stems from our ability to interpret the differing
character of the Zeeman polarization signals which arise from the photospheric
line-of-sight vs. the transverse components of the solar vector magnetic field,
and is likely exacerbated by unresolved structure (non-unity fill fraction) as
well as the disambiguation of the 180 degeneracy in the
transverse-field azimuth. Here we provide a description of this phenomenon, and
discuss issues, which require additional investigation.Comment: 13 pages, 5 figure, Journal of Space Weather and Space Climate,
accepted, 202
Solar wind modeling with the Alfven Wave Solar atmosphere Model driven by HMI-based Near-Real-Time maps by the National Solar Observatory
We explore model performance for the Alfven Wave Solar atmosphere Model
(AWSoM) with near-real-time (NRT) synoptic maps of the photospheric vector
magnetic field. These maps, produced by assimilating data from the Helioseismic
Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO), use a
different method developed at the National Solar Observatory (NSO) to provide a
near contemporaneous source of data to drive numerical models. Here, we apply
these NSO-HMI-NRT maps to simulate three Carrington rotations (CRs): 2107-2108
(centered on 2011/03/07 20:12 CME event), 2123 (integer CR) and 2218--2219
(centered on 2019/07/2 solar eclipse), which together cover a wide range of
activity level for solar cycle 24. We show simulation results, which reproduce
both extreme ultraviolet emission (EUV) from the low corona while
simultaneously matching in situ observations at 1 au as well as quantify the
total unsigned open magnetic flux from these maps