Solar Activity Report: July 20 -26, 2026

 Solar activity remained mostly at low levels during the past week.  The X‑ray intensity hovered between high B-class and low C-class. B-class is defined as the X-ray intensity (brightness) below 10^-6 W/m^2, and C-class starts at 10^-6 W/m^2 as measured in 1-8 Angstrom wavelength range. Most of the activity originated from active region 14493, which produced five M‑class flares. Three impulsive events, M2.5, M1.1, and M3.4, occurred on July 20. Two additional M-class flares, M1.9 and M3.6, were recorded on July 21 and July 22, respectively, with the M3.6 event being the strongest of the week. Another notable event was an M3.2 on July 26 from active region 14494. No Earth‑directed CMEs were observed during this period.

Helioseismic maps of the far hemisphere do not show any significant magnetic activity.

Update on GONG/CTIO

GONG at CTIO* continues to be down in aftermath of an exceptionally powerful winter storm system. Here is a brief update from the Observatory:

The Facilities Operations (FacOps) team were finally able to reach the summit of Tololo on Friday (July 24). 

The access road washed out in many places making it passable only for 4x4 vehicles with very experienced drivers. Work is underway to improve the road's condition so that more staff, and importantly, supplies of fuel and water can reach the site. Unfortunately, more bad weather is forecast for next week and over next weekend.

The observatory ran on generator during the storm, but fortunately, commercial electric power was restored yesterday just as we were about to run out of fuel. We now need to restock, which requires using special all-wheel drive fuel tankers. We are concerned that the commercial electric power remains fragile.

The water system on Tololo is also out of service, and we will likely need to transport water to the mountain.

Yesterday, there was only time for quick external inspections, but these suggest there has not been major damage to the telescopes, and other facilities on Tololo.

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*Cerro Tololo Inter-American Observatory (CTIO) is a complex of astronomical telescopes and instruments located approximately 500 km (310 miles) north of Santiago, and 80 km (50 miles) to the east of La Serena, Chile, at an altitude of 2200 meters (7200 feet).

 

 

Status of GONG Network

Currently, only three GONG stations are in operations (GONG/BB - Big Bear, California, GONG/LE - Learmonth, Australia, and GONG/TD - Teide, Canary Islands). 

GONG/UD is down for the monsoon. 

GONG/CT is down in aftermath of severe winter storm.

GONG/ML is down in aftermath of volcanic eruption: Road access to the Mauna Loa Observatory has been restored. However, there is still no commercial power to the site. Hawaiian Electric is working on restoring the damaged power lines. It plans having electric power to the observatory in Fall 2026.

With three sites down, most recent GONG duty cycle (window function) plot shows gaps in coverage. When the weather cooperates, however, even with 3 sites, the network may achieve a duty cycle above 90% as evident from the most recent window function plot.

For a real-time information about GONG stations, see https://monitor.nso.edu/.

GONG AT CTIO

Over the past few days, Chile has been impacted by an exceptionally powerful winter storm system. The storm brought intense rainfall, strong winds, flooding, landslides, and road closures across the Coquimbo Region. Some areas experienced exceptionally heavy rainfall over a very short period of time. 

 GONG station at the Cerro Tololo Inter-American Observatory was shut down prior to the storm. However, returning to operations will unfortunately take a significant time.  The reports indicate that the parts of paved section of the road to the observatory are washed out. The electric power is also out, likely due to downed power poles. The main network fiber is down, but the microwave backup is still working at present, so there is network access, albeit at much reduced speed. For more recent updates, see here.

Image: The public road leading to Cerro Tololo and Cerro Pachón washed out at the San Carlos ravine. Credit: Elquiglobal via Instagram

It's cloud illusions

For astronomical observations, clouds are nuisance as they block star and sunlight and distract the observations. But some (e.g. cirrus) clouds also convey information about changes in weather or the approaching weather storms that astronomers could use for planning of their observations. Some cirrus clouds may exhibit irisation, when a thin clouds is rainbow-colored as in soap bubbles. Here is one example of such clouds from Boulder, Colorado. Cloud iridescence is caused by the diffraction of the sunlight on small water droplets or ice crystals uniformly distributed inside a cloud.  

Cloud iridescence may also be observed in much more rare noctilucent clouds (or polar mesospheric clouds). These clouds are formed at 75-85 km in Earth atmosphere and contain tiny ice crystals, which can scatter sunlight.  These clouds are observed at twilight when the sun is several (5-15) degrees  below the horizon.  Second photo shows example of noctilucent clouds. 

 

Solar Activity Report: July 6 - 12, 2026

 

Solar activity during the past week showed a significant decrease compared with the preceding week.  By Tuesday, the average X‑ray flux level had declined to the B category level, where it remained despite intermittent M‑ and C‑class flares. The strongest event of the week was an impulsive M4.0 flare on July 7 from active region 14482. This region also produced two additional notable flares; M1.5 on July 8 and M1.1 on July 9. Another M‑class event, a long‑duration M1.1 flare, was observed on July 12 from active region 14485. The locations of these two active regions on July 8 are shown in the attached magnetogram. The least active day of the week was July 11, when flaring was limited to C1‑level activity from AR 14485. These flares generated several CMEs, though none had an Earth‑directed component.  

Helioseismic maps of the far side indicate that three active regions, 14478, 14479, and 14480, remain on the back hemisphere of the Sun not visible from Earth. These regions produced elevated level activity while on the front side, including an X‑class flare and multiple M‑class flares, before rotating to the far side around July 5 - 6. They are expected to return to the front side toward the end of this week or early next week, provided they do not decay over the next few days.

Does the Shutdown of a Single Site Affect the GONG Network Duty Cycle?

The duty cycle measures how many observations are available over a given period. For GONG, it generally represents the fraction of observations obtained during a single day. The six GONG sites distributed across the northern and southern hemispheres were selected to ensure that at least two sites observe at any given time, with no interruption to the observations during the non-observing period of one site. Their locations were carefully chosen based on long‑term weather patterns and year‑round sunlight availability. A detailed study of the duty cycle for individual GONG sites and for the full network clearly demonstrates that the network duty cycle is adversely affected by the shutdown of a particular site only when adjacent sites also lack observations.

For example, the Udaipur (UD) site was turned off on July 8 due to the Indian monsoon. The gap in the network observations on this day (marked in the left figure) is not caused solely by the shutdown of UD - it occurred because the adjacent El Teide (TD) site during the overlapping periods with LE and UD on the same day was down due to a technical issue. Once that issue was resolved the following day, the network duty cycle returned to its usual high value and has remained stable. 

The figure below reinforces this point: on July 7 and 9, both TD (green oval) and Learmonth (LE marked by the red oval) provided observations, and no comparable gap appeared in the window function despite UD being offline. The absence of UD observations is indicated by the brown ovals for July 7 - 9, while the brief overlap between LE and TD on July 7 and 9 (shown by the gray shaded bars) ensued continuity to the observations. Provided TD and LE remain operational, no major duty‑cycle impact is expected during the UD monsoon shutdown.

It is important to note, as mentioned previously, that the Mauna Loa (ML) site in Hawaii has been offline since late November 2022 due to a volcanic eruption, and efforts are ongoing to restore operations. There have been periods when the network duty cycle has dipped for the reasons described above, including weather‑related or technical issues. Even when high duty cycle values can be achieved with fewer observing sites, full operation of all six sites remains essential for the precise determination of the p‑angle (the angle that defines the true solar north in the images) which is critical for measuring subsurface flows using helioseismic methods.  Moreover, a network with a reduced number of operational sites is inherently more vulnerable to lower duty cycle performance over the course of the year.