93 research outputs found
Temporal and Periodic Variations of Sunspot Counts in Flaring and Non-flaring Active Regions
We analyzed temporal and periodic behavior of sunspot counts (SSCs) in
flaring (C, M, or X class flares), and non-flaring active regions (ARs) for the
almost two solar cycles (1996 through 2016). Our main findings are as follows:
i) The temporal variation of monthly means of daily total SSCs in flaring and
non-flaring ARs are different and these differences are also varying from cycle
to cycle; temporal profile of non-flaring ARs are wider than the flaring ones
during the solar cycle 23, while they are almost the same during the current
cycle 24. The second peak (second maximum) of flaring ARs are strongly dominate
during current cycle 24, while this difference is not such a remarkable during
cycle 23. The amplitude of SSCs in the non-flaring ARs are comparable during
the first and second peaks (maxima) of the current solar cycle, while the first
peak is almost not existent in case of the flaring ARs. ii) Periodic variations
observed in SSCs of flaring and non-flaring ARs are quite different in both MTM
spectrum and wavelet scalograms and these variations are also different from
one cycle to another; the largest detected period in the flaring ARs is 113
days, while there are much higher periodicities (327, 312, and 256 days) in
non-flaring ARs. There are no meaningful periodicities in MTM spectrum of
flaring ARs exceeding 45 days during solar cycle 24, while a 113 days
periodicity detected from flaring ARs of solar cycle 23. For the non-flaring
ARs the largest period is 72 days during solar cycle 24, while the largest
period is 327 days during current cycle.Comment: Submitted to Solar Physics, 17 pages, 5 figure
Maximum Coronal Mass Ejection Speed as an Indicator of Solar and Geomagnetic Activities
We investigate the relationship between the monthly averaged maximal speeds
of coronal mass ejections (CMEs), international sunspot number (ISSN), and the
geomagnetic Dst and Ap indices covering the 1996-2008 time interval (solar
cycle 23). Our new findings are as follows. (1) There is a noteworthy
relationship between monthly averaged maximum CME speeds and sunspot numbers,
Ap and Dst indices. Various peculiarities in the monthly Dst index are
correlated better with the fine structures in the CME speed profile than that
in the ISSN data. (2) Unlike the sunspot numbers, the CME speed index does not
exhibit a double peak maximum. Instead, the CME speed profile peaks during the
declining phase of solar cycle 23. Similar to the Ap index, both CME speed and
the Dst indices lag behind the sunspot numbers by several months. (3) The CME
number shows a double peak similar to that seen in the sunspot numbers. The CME
occurrence rate remained very high even near the minimum of the solar cycle 23,
when both the sunspot number and the CME average maximum speed were reaching
their minimum values. (4) A well-defined peak of the Ap index between 2002 May
and 2004 August was co-temporal with the excess of the mid-latitude coronal
holes during solar cycle 23. The above findings suggest that the CME speed
index may be a useful indicator of both solar and geomagnetic activities. It
may have advantages over the sunspot numbers, because it better reflects the
intensity of Earth-directed solar eruptions
Properties of Umbral Dots as Measured from the New Solar Telescope Data and MHD Simulations
We studied bright umbral dots (UDs) detected in a moderate size sunspot and
compared their statistical properties to recent MHD models. The study is based
on high resolution data recorded by the New Solar Telescope at the Big Bear
Solar Observatory and 3D MHD simulations of sunspots. Observed UDs, living
longer than 150 s, were detected and tracked in a 46 min long data set, using
an automatic detection code. Total 1553 (620) UDs were detected in the
photospheric (low chromospheric) data. Our main findings are: i) none of the
analyzed UDs is precisely circular, ii) the diameter-intensity relationship
only holds in bright umbral areas, and iii) UD velocities are inversely related
to their lifetime. While nearly all photospheric UDs can be identified in the
low chromospheric images, some small closely spaced UDs appear in the low
chromosphere as a single cluster. Slow moving and long living UDs seem to exist
in both the low chromosphere and photosphere, while fast moving and short
living UDs are mainly detected in the photospheric images. Comparison to the 3D
MHD simulations showed that both types of UDs display, on average, very similar
statistical characteristics. However, i) the average number of observed UDs per
unit area is smaller than that of the model UDs, and ii) on average, the
diameter of model UDs is slightly larger than that of observed ones.Comment: Accepted by the AP
First high-resolution look at the quiet Sun with ALMA at 3 mm
We present an overview of high resolution quiet Sun observations, from disk
center to the limb, obtained with the Atacama Large mm and sub-mm Array (ALMA)
at 3 mm. Seven quiet Sun regions were observed with resolution of up to 2.5" by
4.5". We produced both average and snapshot images by self-calibrating the ALMA
visibilities and combining the interferometric images with full disk solar
images. The images show well the chromospheric network, which, based on the
unique segregation method we used, is brighter than the average over the fields
of view of the observed regions by K while the intranetwork is less
bright by K, with a slight decrease of the network/intranetwork
contrast toward the limb. At 3 mm the network is very similar to the 1600 \AA\
images, with somewhat larger size. We detected for the first time spicular
structures, rising up to 15" above the limb with a width down to the image
resolution and brightness temperature of 1800 K above the local
background. No trace of spicules, either in emission or absorption, was found
on the disk. Our results highlight ALMA's potential for the study of the quiet
chromosphere.Comment: Astronomy and Astrophysics (Letters), in pres
- …