The recently launched Hinode spacecraft is one of the latest observatories to probe the sun from afar. Credit: JAXA/NASA/SAOĮven though the sun is the closest star to Earth and has been studied for hundreds of years, it still holds surprises. In comparison, the X-Ray Telescope sees a detailed structure composed of discontinuous, distinguishable threads highly interwoven with the surrounding plasma.

Similar photos taken previously by the Yohkoh spacecraft showed only a continuous, S-shaped formation. This image shows the magnetic field structure of active region 10940 as it nears the limb (visible edge) of the Sun. Additionally, any predicted CIR or CH HSS influences are explained in more detail in the forecast discussion.Some imagine the shape of a swan in this recent photograph of a portion of the sun's surface taken with the X-Ray Telescope on board the Hinode spacecraft. SWPC forecasters take into account any possible effects of CIR and CH HSS activity when forecasting the anticipated levels of overall planetary geomagnetic response for each 3-hour synoptic period over the next three days as detailed in the 3-day forecast. The larger and more expansive coronal holes can often be a source for high solar wind speeds that buffet Earth for many days.īecause of their potential for escalated geomagnetic activity and possible storming (G1 or higher), forecasters analyze coronal holes closely and also note them on the daily synoptic drawing. Geomagnetic storms are classified using a five-level NOAA Space Weather Scale. Strong CIRs and the faster CH HSS can impact Earth’s magnetosphere enough to cause periods of geomagnetic storming to the G1-G2 (Minor to Moderate) levels although rarer cases of stronger storming may also occur. Generally, coronal holes located at or near the solar equator are most likely to result in any CIR passage and/or higher solar wind speeds at Earth. After passage of the CIR and upon transition into the CH HSS flow, the overall IMF strength will normally begin to slowly weaken. As the CH HSS begins to arrive at Earth, solar wind speed and temperature increase, while particle density begins to decrease.

The CIR can result in particle density enhancement and interplanetary magnetic field (IMF) strength increases preceding onset of the CH HSS. From the perspective of a fixed observer in interplanetary space, the CIR will be seen to lead the coronal hole high speed stream (CH HSS). As the high speed stream interacts with the relatively slower ambient solar wind, a compression region forms, known as a co-rotating interaction region (CIR). Persistent coronal holes are long-lasting sources for high speed solar wind streams. It is also possible for coronal holes to develop in isolation from the polar holes or for an extension of a polar hole to split off and become an isolated structure. Coronal holes are most prevalent and stable at the solar north and south poles but these polar holes can grow and expand to lower solar latitudes. The more persistent coronal holes can sometimes last through several solar rotations (27-day periods). This open, magnetic field line structure allows the solar wind to escape more readily into space, resulting in streams of relatively fast solar wind and is often referred to as a high speed stream in the context of analysis of structures in interplanetary space.Ĭoronal holes can develop at any time and location on the Sun, but are more common and persistent during the years around solar minimum. They appear dark because they are cooler, less dense regions than the surrounding plasma and are regions of open, unipolar magnetic fields. Coronal holes appear as dark areas in the solar corona in extreme ultraviolet (EUV) and soft x-ray solar images.

Sun corona x rays