Large coronal hole and future space weather event?

Solar magnetic fields usually come in pairs: active regions have two opposite polarities, similar to bar magnets. One can identify some of these bipolar structures in a solar magnetogram from GONG on the right with positive/negative polarity fields shown as white/black halftones. Sometimes, the patterns are more complex with multiple positive and negative polarities.  Magnetic flux in these twin or multi-polarity regions is usually well-balanced: magnetic field lines originating in one polarity connect to the opposite polarity in the same active region or its surroundings. Corona is bright above closed magnetic field areas (active regions, see SDO/AIA image on far right). There are, however, areas which have predominantly single polarity magnetic field. Magnetic field lines originating in these unipolar areas may not connect to the solar surface, but extend to the interplanetary space. These areas of opened magnetic field coincide with coronal holes, areas were the corona appears much darker. One of these large coronal holes is now crossing solar visible disk. Coronal holes are associated with streams of fast solar wind, which cause moderate geomagnetic storms. We should expect a moderate geomagnetic storm activity in several days after the corona hole passes solar central meridian. 

Rare "double-decker" filament eruption

Traditional model represents the chromospheric filaments as dense, cold (relative to its surroundings) material seating in the lower part of horizontal magnetic flux tubes. In this model, the magnetic forces support the filament material against gravity, keeping it from falling down to the solar surface. The model explains many properties of filaments including their relation with the coronal mass ejections. However, the magnetic flux tube is continuous structure, and when the filament erupts, it is expected that the entire flux tube erupts with it. There are, however, instances when only a portion of filament material erupts leaving other part intact. Such filament splitting was explained in the framework of so-called double-decker filaments, when the magnetic reconnection results in splitting of magnetic flux tube into two separate tubes. A filament eruption on 6 September 2025 at 14:51 UT observed by GONG at Cerro Tololo, Chile  captured the filament splitting into two separate filaments. There are some small flare-like brightennings, but no X-ray class flare.  Also, no CME was associated with this event, and so, this is a failed filament eruption. These observations provide a strong support for the double-decker filament model. See for yourself.

What is a double-decker filament?

It refers to two separate filaments situated above the same polarity inversion line. Rui Liu et al (2012, doi:10.1088/0004-637X/756/1/59) proposed two magnetic configuration of a double-decker filament: (a) the upper and lower branches are flux ropes, (b) the upper branch is the flux rope and the lower one is the sheared arcade. Such configuration allows the eruption of one of the filaments, without impacting the other filament.  The filament eruption could be triggered by a loss of equilibrium due to flux imbalance, the torus or kink instabilities. Sunspot rotation was observed prior to some double-decker filament eruptions. More recent studies (e.g., Dongxu Liu et al 2025, doi: 10.3847/2041-8213/addfca) provide support to torus instability as a trigger for the filament eruption.

UPDATED: New data product in development: GONG H-Alpha Integral Carrington synoptic maps

NISP group is seeking feedback on a new data product currently in development: GONG H-Alpha integral Carrington synoptic maps. We are especially interested in suggestions regarding the appropriate set of keywords to include in the FITS file headers, as well as comments on the current map format.

At present, the maps are provided in Carrington sin(latitude)–longitude coordinates, with a resolution of 360 × 720 pixels. Observations from selected GONG sites are corrected for limb darkening and uniformly scaled in intensity before being merged into the final synoptic map.

A selection of FITS files is available at the following link: https://drive.google.com/drive/folders/1M0ZwpBA_SW8JuMwlDP0Se75M2IQkCGQ3?usp=sharing

Please email your comments to nispdata@nso.edu by 15 October 2025.

C-class two-ribbon flare with filament eruption

 

On 4 September 2025 at 19:10 UT, C3.4 class flare erupted from NOAA active region 14206. The flare was captured by GONG station at Cerro Tololo, Chile. A portion of an active region filament situated near the main sunspot of this region starts slowly rising about 30 minutes before the eruption. After the eruption,  dark filament material can be seen in a low part of image as material is leaving the Sun. After the filament erupts, two bright ribbons develop, moving apart from the past filament location. This is a classical two-ribbon flare, which is usually accompanied by a coronal mass ejection (CME). The eruption took place near the solar central meridian, and if it was a CME, it would likely be Earth-directed. In this movie  created with different image scaling, one can briefly see a dark circular front centered at the eruption site (see image below). This is a signature of the Moreton (blast) wave, which maybe another indication of CME.  Unfortunately, LASCO C3 coronagraph has about 4 hour gap in observations between 16:54 UT and 21:06 UT, and thus, similar to previous event, it is not clear if it was a CME or not.

 

 

 

Blast from the past

 In August 1972, a series of solar flares and associated geomagnetic storms led to widespread communications disturbances and power outages. On August 4th, the geomagnetic storm caused a nearly instantaneous detonation of dozens of sea mines installed by the US during the Vietnam War south of Hai Phong. The August 4th flare, which occurred between the Apollo 16 and Apollo 17 missions, led to a significant increase in the radiation level in the interplanetary space. It was estimated that for the astronauts on the moonwalk, the radiation dose equivalents would have been clinically significant, including nausea, vomiting, a very high probability of cataract formation, with a slight increase in the probability of death. This flare, which occurred more than 50 years ago, was well-observed by the H-alpha flare patrol telescope at the National Solar Observatory at Sacramento Peak. Image on the left shows the Sun before the flare, and on the right is the flare in progress. You can also see that a portion of filament left of the flaring region had disappeared. These are the signs of a coronal mass ejection erupting from this area of the Sun. Study of the past events may bring invaluable information  about how such strong eruptions develop and help us to prepare for traveling to the Moon and Mars.

GONG Big Bear station

Broadband image from GONG/BB

GONG Big Bear station is exhibiting an unusually large number of camera resets. Each reset interrupts normal observing sequence, and impact the continuity of observations. This happen after recent unplanned power outage.  Engineering team is developing a mitigation approach to resolve the issue.

Flares, filament eruptions, but no CME?

Major (M- and X-class) flares and filament eruptions are usually accompany CMEs, but not always. On 31 August 2025 at about 14:00 UT, M1.3-class flare was recorded in NOAA active regions 14197. This is the region that had about hundred sunspots early this week. The flare activated large quiescent filament south of this region with a partial filament eruption at about 16:15 UT  (upper panel). Then, at about 18:00 UT a small two-ribbon flare and filament eruption were observed in NOAA region 14202 to the East of region 14197 (second panel from the top). See GONG video of these events at the bottom panel.  Despite this activity, there was no obvious sign of CMEs in LASCO coronagraph. There is gap in observations in LASCO C2 between 17:24 UT and 18:36 UT, and coronal streamers appear to be pushed apart during this gap. So, maybe it was a CME but LASCO missed it? Or maybe these were the  failed filament eruptions?