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Register a new userReal-time solar wind prediction based on SDO/AIA coronal hole data
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T. Rotter
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We present an empirical model based on the visible area covered by coronal holes close to the central meridian in order to predict the solar wind speed at 1 AU with a lead time up to four days in advance with a 1hr time resolution. Linear prediction functions are used to relate coronal hole areas to solar wind speed. The function parameters are automatically adapted by using the information from the previous 3 Carrington Rotations. Thus the algorithm automatically reacts on the changes of the solar wind speed during different phases of the solar cycle. The adaptive algorithm has been applied to and tested on SDO/AIA-193A observations and ACE measurements during the years 2011-2013, covering 41 Carrington Rotations. The solar wind speed arrival time is delayed and needs on average 4.02 +/- 0.5 days to reach Earth. The algorithm produces good predictions for the 156 solar wind high speed streams peak amplitudes with correlation coefficients of cc~0.60. For 80% of the peaks, the predicted arrival matches within a time window of 0.5 days of the ACE in situ measurements. The same algorithm, using linear predictions, was also applied to predict the magnetic field strength from coronal hole areas but did not give reliable predictions (cc~0.2).
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We report on the variability of rotation periods of solar coronal layers with respect to temperature (or, height). For this purpose, we have used the observations from Atmospheric Imaging Assembly (AIA) telescope on board Solar Dynamics Observatory (SDO) space mission. The images used are at the wavelengths 94 {AA}, 131 {AA}, 171 {AA}, 193 {AA}, 211 {AA}, and 335 {AA} for the period from 2012 to 2018. Analysis of solar full disk images obtained at these wavelengths by AIA is carried out using flux modulation method. Seventeen rectangular strips/bins at equal interval of 10 degrees (extending from 80 degree South to 80 degree North on the Sun) are selected to extract a time series of extreme ultraviolet (EUV) intensity variations to obtain auto-correlation coefficient. The peak of Gaussian fit to first secondary maxima in the autocorrelogram gives synodic rotation period. Our analysis shows the differential rotation with respect to latitude as well as temperature (or, height). In the present study, we find that the sidereal rotation periods of different coronal layers decrease with increasing temperature (or, height). Average sidereal rotation period at the lowest temperature (~ 600000 Kelvin) corresponding to AIA-171 {AA} which originates from the upper transition region/quiet corona is 27.03 days. The sidereal rotation period decreases with temperature (or, height) to 25.47 days at the higher temperature (~10 million Kelvin) corresponding to the flaring regions of solar corona as seen in AIA-131 {AA} observations.
Using the multi-wavelength data from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) spacecraft, we study a jet occurred in coronal hole near the northern pole of the Sun. The jet presented distinct helical upward motion during ejection. By tracking six identified moving features (MFs) in the jet, we found that the plasma moved at an approximately constant speed along the jets axis, meanwhile, they made a circular motion in the plane transverse to the axis. Inferred from linear and trigonometric fittings to the axial and transverse heights of the six tracks, the mean values of axial velocities, transverse velocities, angular speeds, rotation periods, and rotation radiuses of the jet are 114 km s$^{-1}$, 136 km s$^{-1}$, 0.81degr s$^{-1}$, 452 s, and 9.8 $times$ 10$^{3}$ km respectively. As the MFs rose, the jet width at the corresponding height increased. For the first time, we derived the height variation of the longitudinal magnetic field strength in the jet from the assumption of magnetic flux conservation. Our results indicate that, at the heights of 1 $times$ 10$^{4}$ $sim$ 7 $times$ 10$^{4}$ km from jet base, the flux density in the jet decreased from about 15 to 3 G as a function of B=0.5(R/R$_{sun}$-1)$^{-0.84}$ (G). A comparison was made with the other results in previous studies.
In this paper, we carry out multiwavelength observations of three recurring jets on 2014 November 7. The jets originated from the same region at the edge of AR 12205 and propagated along the same coronal loop. The eruptions were generated by magnetic reconnection, which is evidenced by continuous magnetic cancellation at the jet base. The projected initial velocity of the jet2 is 402 km s. The accelerations in the ascending and descending phases of jet2 are not consistent, the former is considerably larger than the value of solar gravitational acceleration at the solar surface, while the latter is lower than solar gravitational acceleration. There are two possible candidates of extra forces acting on jet2 during its propagation. One is the downward gas pressure from jet1 when it falls back and meets with jet2. The other is the viscous drag from the surrounding plasma during the fast propagation of jet2. As a contrast, the accelerations of jet3 in the rising and falling phases are constant, implying that the propagation of jet3 is not significantly influenced byextra forces.
The Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO) returns high-resolution images of the solar atmosphere in seven extreme ultraviolet wavelength channels. The images are processed on the ground to remove intensity spikes arising from energetic particles hitting the instrument, and the despiked images are provided to the community. In this work a three-hour series of images from the 171 A channel obtained on 2017 February 28 was studied to investigate how often the despiking algorithm gave false positives caused by compact brightenings in the solar atmosphere. The latter were identified through spikes appearing in the same detector pixel for three consecutive frames, and 1096 examples were found from the 900 image frames. These three-spikes were assigned to 126 dynamic solar features, and it is estimated that the three-spike method identifies 25% of the total number of features affected by despiking. For any 10 minute sequence of AIA 171 A images there are therefore around 28 solar features that have their intensity modified by despiking. The features are found in active regions, quiet Sun and coronal holes and, in relation to solar surface area, there is a greater proportion within coronal holes. In 96% of the cases, the despiked structure is a compact brightening of size 2 arcsec or less and the remaining 4% have narrow, elongated structures. In all cases, the events are not rendered invisible by the AIA processing pipeline, but the total intensity over the events lifetimes can be reduced by up to 67%. Scientists are recommended to always restore the original intensities to AIA data when studying short-lived or rapidly-evolving features that exhibit fine-scale structure.
We present a study of the frequency of transient brightenings in the core of solar active regions as observed in the Fe XVIII line component of AIA/SDO 94 A filter images. The Fe XVIII emission is isolated using an empirical correction to remove the contribution of warm emission to this channel. Comparing with simultaneous observations from EIS/Hinode, we find that the variability observed in Fe XVIII is strongly correlated with the emission from lines formed at similar temperatures. We examine the evolution of loops in the cores of active regions at various stages of evolution. Using a newly developed event detection algorithm we characterize the distribution of event frequency, duration, and magnitude in these active regions. These distributions are similar for regions of similar age and show a consistent pattern as the regions age. This suggests that these characteristics are important constraints for models of solar active regions. We find that the typical frequency of the intensity fluctuations is about 1400s for any given line-of-sight, i.e. about 2-3 events per hour. Using the EBTEL 0D hydrodynamic model, however, we show that this only sets a lower limit on the heating frequency along that line-of-sight.
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