( CHHSS ) Coronal Hole High SpeedStream: When a hole appears in thecorona, a fast flowing stream of charged particles flows out.

(CME ) CoronalMass Ejection: Coronal mass ejections areexplosions in the Sun's corona that spew out high-energy chargedparticles. CME's can seriously disrupt the Earth's environmentthrough radiation, which arrives only 8 minutes after being released,and through very energetic particles pushed along by the shock waveof the CME.

( CIR) Co-rotating InteractionRegion: When high speed solar wind overtakesslow speed wind, it creates something known as a co-rotatinginteraction region. These interaction regions consist of solar windwith very high densities and strong magnetic fields.

( SSBC) Solar SectorBoundary Crossing: Occurs when the polarityof the interplanetary magnetic field (IMF) reverses. The orientationof the IMF may be such that it might temporarily cancel the Earth'sgeomagnetic field, allowing solar energy to enter the upperatmosphere causing large disturbances in the F and E layers resultingin extensive HF outages.

Geoeffective:Certain conditions can beused to reliabily predict large changes in the Earth's geomagneticfield. This oftens means changes in the height, density andreflectiveness (structuring) of the E and F layers. This is a keyword for HF radio operators and planners.

Plage:Bright white areassurrounding a sunspot group. In general, it appears at the end cycleof a particular sunspot group.

EruptiveProminence:A prominence on the sun that isformed from active material above the chromosphere and reaches highaltitudes on the sun at great speed.



CH HSS -Coronal Hole - High Speed Stream

When we look at satellite imagery at a wavelength of28,4 nanometer, it shows us the hot outer layers of the atmosphere ofthe Sun, to be specific: the corona. The bright areas shows us hotand dense gas that's captured by the magnetic field of the Sun. Thedark and empty areas are places where the magnetic field of the Sunreaches into space so that hot gas can escape. These dark areas arecoronal holes.

The magnetic field around a coronal hole is differentthan the rest of the Sun. Instead of returning to the surface, thesemagnetic field lines stay open and stretch out into space. At themoment we do not yet know where they reconnect. Instead of keepingthe hot gas together, these open magnetic field lines cause a coronalhole to form, where solar wind can escape at high speeds. When acoronal hole is positioned near the centre of the Earth-facing solardisk, these hot gasses flow to Earth at a higher speed than theregular solar wind and cause geomagnetic disturbances on Earth withenhanced auroral activity on high latitudes.


CME - CoronalMass Ejections

Coronal mass ejections (CMEs) are huge explosions ofmagnetic field and plasma from the Sun's corona. When CMEs impact theEarth's magnetosphere, they are responsible for geomagnetic stormsand enhanced aurora. CMEs originate from highly twisted magneticfield structures, or "flux ropes", on the Sun, often visualized bytheir associated "filaments" or "prominences", which are relativelycool plasmas trapped in the flux ropes in the corona. When these fluxropes erupt from active regions on the Sun (regions associated withsunspots and very strong magnetic fields), they are often accompaniedby large solar flares; eruptions from quiet regions of the Sun, suchas the "polar crown" filament eruptions, sometimes do not haveaccompanying flares.

CMEs travel outward from the Sun typically at speedsof about 300 kilometers per second, but can be as slow as 100kilometers per second or faster than 3000 kilometers per second. Thefastest CMEs erupt from large sunspot active regions, powered by thestrongest magnetic field concentrations on the Sun. These fast CMEscan reach Earth in as little as 14--17 hours. Slower CMEs, typicallythe quiet region filament eruptions, take several days to traversethe distance from the sun to Earth. Because CMEs have an embeddedmagnetic field that is stronger than the background field of thesolar wind, they will expand in size as they propagate outward fromthe Sun. By the time they reach the Earth, they can be so large theywill fill half the volume of space between the Sun and the Earth.Because of their immense size, slower CMEs can take as long as 24 to36 hours to pass over the Earth, once the leading edge has arrived.

CMEs that are traveling faster than the solar windplasma's fast mode wave speed (the space equivalent of the Earth'ssound speed) will generate a shock wave, just like an airplanetraveling faster than the speed of sound generates a sonic boom.These shock waves accelerate charged particles ahead of them tocreate much of the solar radiation storm affiliated with large-scalesolar eruptions. Often, the first sign of a CME hitting the Earthenvironment is the plasma density jump due to the shock wave'spassage.

The size, speed, direction, and density of a CME areimportant parameters to determine when trying to predict if and whenit will impact Earth. We can estimate these properties of a CME usingobservations from an instrument known as a coronagraph, which blocksthe bright light of the solar disk, just as the moon does in a totalsolar eclipse, allowing the outer solar atmosphere (chromosphere andcorona) to be observed. CMEs show up as bright clouds of plasmamoving outward through interplanetary space.

In order to predict the strength of the resultinggeomagnetic storm, estimates of the magnetic field strength anddirection are important. At the present time, the magnetic fieldcannot be determined until it is measured as the CME passes over amonitoring satellite. If the magnetic field direction of the CME isopposite to that of the Earth's dipolar magnetic field, the resultinggeomagnetic disturbance or storm will be larger than if the fieldsare in the same direction. Some CMEs show predominately one directionof magnetic field in their passage past the Earth, but most exhibitchanging field directions as the large magnetic cloud passes over ourrelatively tiny magnetosphere, so most CMEs that impact the Earth'smagnetosphere will at some point have magnetic field conditions thatfavor the generation of geomagnetic storming with the associatedauroral displays and geomagnetically induced currents in the ground.


CIRCo-rotating Interaction Region

The solar wind continuously flows outward from theSun and consists mainly of protons and electrons in a state known asa plasma. Solar magnetic field is embedded in the plasma and flowsoutward with the solar wind.

Different regions on the Sun produce solar wind ofdifferent speeds and densities. Coronal holes produce solar wind ofhigh speed, ranging from 500 to 800 kilometers per second. The northand south poles of the Sun have large, persistent coronal holes, sohigh latitudes are filled with fast solar wind. In the equatorialplane, where the Earth and the other planets orbit, the most commonstate of the solar wind is the slow speed wind, with speeds of about400 kilometers per second. This portion of the solar wind forms theequatorial current sheet.

During quiet periods, the current sheet can be nearlyflat. As solar activity increases, the solar surface fills withactive regions, coronal holes, and other complex structures, whichmodify the solar wind and current sheet. Because the Sun rotatesevery 27 days, the solar wind becomes a complex spiral of high andlow speeds and high and low densities that looks like the skirt of atwirling ballerina. When high speed solar overtakes slow speed wind,it creates something known as a corotating interaction region. Theseinteraction regions consist of solar wind with very high densitiesand strong magnetic fields

Above the current sheet, the higher speed solar windtypically has a dominant magnetic polarity in one direction and belowthe current sheet, the polarity is in the opposite direction. As theEarth moves through this evolving ballerina skirt, it is sometimeswithin the heliospheric current sheet, sometimes above it andsometime below it. When the magnetic field of the solar wind switchespolarity, it is a strong indication that Earth has crossed thecurrent sheet. The location of the Earth with respect to the currentsheet is important because space weather impacts are highly dependenton the solar wind speed, the solar wind density, and the direction ofthe magnetic field embedded in the solar wind.

Each of the elements mentioned above play a role inspace weather. High speed winds bring geomagnetic storms while slowspeed winds bring calm space weather. Corotating interaction regionsand to a lesser extent, current sheet crossings, can also causegeomagnetic disturbances. Thus specifying and forecasting the solarwind is critical to developing forecasts of space weather and itsimpacts at Earth.


SSBC Solar Sector Boundary Crossing

As the solar wind flows away from the Sun, theinterplanetary magnetic field (IMF) is carried with it and has aspiral shape. Along the ecliptic plane (direct line between the sunand Earth), the IMF generally has 2 or 4 sectors per solar rotation(27 days) where it is pointed toward or away from the Sun. Thesurface separating the polarities is called the heliospheric currentsheet. A sector boundary crossing occurs when the polarity of the IMFreverses. A well defined sector boundary crossing has a uniform fielddirection for about 4 days before and after the crossing.

Earth's geomagnetic field points north at themagnetopause (the point of contact between our magnetosphere and theIMF. If the IMF happens to point south at contact (scientific term,southward Bz) the two fields link causing partial cancellation ofEarth's geomagnetic field, in other words, opening a temporary doorfor solar energy to enter our atmosphere.