When is local geomagnetic midnight

See single event upset or electrostatic discharge. Sunspots and faculae are observed in the photosphere. Magnetic fields are more intense in plage, and temperatures are higher than in surrounding, quiescent regions. Like the ionosphere, the plasmasphere tends to co-rotate with the Earth. PCAs generally originate with major solar flares, beginning within a few hours of the event and maximizing within a day or two of onset.

In practice, the absorption is inferred from the proton flux at energies greater than 10 MeV, so that PCAs and proton events are simultaneous. However, the transpolar radio paths may be disturbed for days, up to weeks, following the end of a proton event. It is distinguished from a sunspot by its short lifetime, 10 to minutes. Lifetimes are several hours. The features appear as bright structures above the solar limb and as dark filaments when seen projected against the solar disk. They are most clearly and most often observed in H-alpha.

The start time of the event is defined as the earliest time at which event thresholds have been reached. The end time is the last time 10 p. This definition allows multiple injections from flares and interplanetary shocks to be encompassed by a single event. There are two main patterns: Pc a continuous, almost sinusoidal pattern , and Pi an irregular pattern.

Pulsations occur at magnetically quiet as well as disturbed times. Q Q index I5-minute index of geomagnetic activity for high-latitude auroral stations. After quiet diurnal variations are removed, Q is the largest deviation scaled from the undisturbed level for the two horizontal components. This differs from the K index, which is scaled from the largest relative deviation. The I5-minute periods are centered on the hour and at 15, 30, and 45 minutes past each hour. The range of Q is from 0 to 11; the upper limit, in nanotesla, for each index value is given below.

Except in an occasional activated phase, shows little large-scale motion, develops very slowly, and has a lifetime of several solar rotations. Quiescent prominences form within the remnants of decayed active regions, in quiet areas of the Sun between active regions, or at high solar latitudes where active regions seldom form. See filament. Riometer and neutron monitor deviations are also measured relative to a QDC. R R-number Radar returns from electron density irregularities in auroral regions.

The strength of radar auroral returns is aspect dependent. There are two belts. The inner belt is part of the plasmasphere and corotates with the Earth; its maximum proton density lies near km. Inner belt protons are mostly high energy MeV range and originate from the decay of secondary neutrons created during collisions between cosmic rays and upper atmospheric particles.

The outer belt extends on to the magnetopause on the sunward side. The altitude of maximum proton density is near 16,, km. Outer belt protons are lower energy about eV to 1 MeV and come from the solar wind.

The outer belt is also characterized by highly variable fluxes of energetic electrons. Van Allen. See Appendix A. Rayleigh-Taylor instability A fluted or ripple-like instability that can develop on a fluid or plasma boundary surface and propagate along it. This instability is often invoked to explain phenomena in the ionosphere and magnetosphere.

Reconnection is invoked to explain the energization and acceleration of the plasmas that are observed in solar flares, magnetic substorms, and elsewhere in the solar system. It identifies relatively cooler regions of the corona. See also active region. RI The international standard relative sunspot number. It is expressed in hours, minutes, and seconds the circumference of the celestial equator is defined as 24 hours.

The current is produced by the gradient and curvature drift of the trapped charged particles. The ring current is greatly augmented during magnetic storms because of the hot plasma injected from the magnetotail.

This increase in the ring current causes a worldwide depression of the horizontal geomagnetic field during a magnetic storm. The absorption of cosmic noise in the polar regions is very sensitive to the solar low-energy cosmic ray flux. Absorption events are known as PCAs polar cap absorption and are primarily associated with major solar flares. Penumbrae are typically rudimentary during the sunspot formative and decay phases. S satellite anomaly The usually undesirable response of spacecraft systems to variations in the space environment.

Large and varying low-to-medium energy particle fluxes can result in a charge buildup between spacecraft components especially during the eclipse season and during spacecraft maneuvers.

Atmospheric drag on spacecraft below approximately 1, km can increase during geomagnetic storms, resulting in cross-track and in-track orbit errors and orientation problems. Various communication interference problems result during solar radio bursts from flares when the Sun is within the field of view of the ground tracking dish.

Ionospheric irregularities during geomagnetic storms can cause radio telemetry scintillation and fading. S-band Radio frequencies between 1. For satellite communication. The term usually refers to frequencies used for Earth-space communication near 2.

S component The slowly varying weeks or longer fluctuation observed in solar radio emission at microwave frequencies wavelengths from cm. SC See sudden commencement. It is positively correlated with spread F and to a lesser degree, sporadic E. Scintillation effects are the most severe at low latitudes, but can also be a problem at high latitudes, especially in the auroral oval and over the polar caps.

The sector boundary separating fields of opposite polarity is normally narrow, passing the Earth within minutes to hours as opposed to the week or so needed for passage of a typical sector. The solar wind velocities in the boundary region are typically among the lowest observed.

SFE Solar flare effect. See crochet. SI See sudden impulse. SID See sudden ionospheric disturbance. The 1st and 13th months are given a weight of 0. Five standard terms are used to describe the activity observed or expected: Very low x-ray events less than C-class.

Low - C-class x-ray events. Moderate - isolated one to 4 M-class x-ray events. High - several 5 or more M5 or greater x-ray events. Radiation at all wavelengths from all parts of the solar disk is included. Its value is approximately 2. The terms used to refer to the coordinates are defined as follows: P-angle: The position angle between the geocentric north pole and the solar rotational north pole measured eastward from geocentric north.

Once P, B, and L are known, the latitude, central meridian distance, and longitude of a specific solar feature can be determined as follows: Latitude. The difference between sidereal and synodic rates is the Earth orbital motion of 0. The supposed solar signature of an interplanetary sector boundary. The total intensity of the interplanetary magnetic field is nominally 5 nT. There are two of these points, halfway between the equinoxes; they mark the beginning of summer and winter.

South Atlantic anomaly SAA A region of the Earth centered near 25S and 50W near the Atlantic coast of Brazil of low geomagnetic field intensity owing to the fact that the geomagnetic field axis is offset from the center of the Earth. The result is that the F region see ionosphere is highly variable in this region, and satellites in low Earth orbits suffer greater radiation doses when they pass through the SAA.

There is a corresponding location of maximum geomagnetic field intensity in Southeast Asia. Occasionally this term is used in a more limited sense to mean surface charging.

The total lifetime is 5 to 10 minutes. Sporadic E can occur during daytime or nighttime, and varies markedly with latitude.

Es can be associated with thunderstorms, meteor showers, solar, and geomagnetic activity. Sprays are usually seen in H-alpha with complex and rapidly changing form. There is little evidence that sprays are focused by magnetic fields. In equatorial latitudes spread F is most commonly observed at night and may be negatively correlated with geomagnetic activity.

At high latitudes spread F occurs throughout the daytime and is positively correlated with magnetic activity. The latitude of minimum occurrence of spread F is near 30 degrees magnetic latitude. SPY See spray. Sq The diurnal variation of the geomagnetic field. The Sq variation is explained in terms of solar tidal motions of the ionosphere and thermally driven ionospheric winds. SSB See solar sector boundary. SSC See sudden commencement. It begins at an altitude of temperature minimum at approximately 13 km and defines a layer of increasing temperature up to about 50 km.

STRATWARM A code word designating a major disturbance of the winter, polar, middle atmosphere from the tropopause to the ionosphere, lasting for several days at a time and characterized by a warming of the stratospheric temperature by some tens of degrees. There is no evidence that stratwarms are caused by solar events, or that they affect the lower atmosphere.

The primary effect is upon HF propagation. The magnitude of the substorm is largest in the auroral zone, potentially reaching several thousand nanotesla. A substorm corresponds to an injection of charged particles from the magnetotail into the auroral oval. SCs occur almost simultaneously worldwide but with locally varying magnitudes.

An SI becomes an SC if a storm follows. Anomalies include short wave fades, enhancements of atmospherics, phase shifts, cosmic noise absorptions, and signal enhancements. Sunspots are concentrations of magnetic flux, typically occurring in bipolar clusters or groups. They appear dark because they are cooler than the surrounding photosphere. Larger and darker sunspots sometimes are surrounded completely or partially by penumbrae.

The dark centers are umbrae. The smallest, immature spots are sometimes called pores. Z the modified Zurich class of the group : A-A small single sunspot or very small group of spots with the same magnetic polarity, without penumbra. B-Bipolar sunspot group with no penumbra. C-An elongated bipolar sunspot group. E-An elongated bipolar sunspot group with penumbra on both ends.

F-An elongated bipolar sunspot group with penumbra on both ends. H-A unipolar sunspot group with penumbra. Class H sunspot groups become compact Class D or larger when the penumbra exceeds 5 degrees in longitudinal extent.

The polarity pattern of the magnetic field reverses with each cycle. Other solar phenomena, such as the The cells are presumably convective in origin with weak upward motions in the center, downward motions at the borders, and horizontal motions of typically 0. Magnetic flux is more intense along the borders of the cells.

Surges typically last 10 to 20 minutes and tend to recur at a rate of approximately 1 per hour. Surges are linear and collimated in form, as if highly directed by magnetic fields. SWF See short wave fade. T TEC See total electron content. See estimated hemispherical power input. It begins above the mesosphere at about km and extends to the exosphere. Units are electrons per square meter.

This number is significant in determining ionospheric effects such as refraction, dispersion, and group delay on radio waves, and can be used to estimate critical frequencies. The TEC is strongly affected by solar and geomagnetic activity.

The transition region is only a few thousand kilometers thick. U U-burst A radio noise burst associated with some flares. It has a U-shaped appearance in an intensity vs. The minimum intensity falls roughly between and MHz. A U-burst is sometimes called a Castelli U.

UHF See ultrahigh frequency. UV See ultraviolet. V Van Allen radiation belts See radiation belts. Compare autumnal equinox. VHF See very high frequency. VLF See very low frequency. W white light WL The sum of all visible wavelengths of light nm so that all colors are blended to appear white to the eye.

No pronounced contribution from any one spectral line or light-emitting element is implied. This rare continuum emission is caused by energetic particle beams bombarding the lower solar atmosphere. Such flares are usually strong x-ray, radio, and particle emitters. WL See white light. Wolf number An historic term for sunspot number. In , R. Wolf of Zurich originated the general procedure for computing the sunspot number. The record of sunspot numbers that he began has continured to this day.

Solar-terrestrial conditions and forecasts are broadcast at 18 minutes past the hour. X X-band Designates those radio frequencies between 5. It is a midday minimum given in terms of x-ray flare class. The time-intensity profile of soft x-ray bursts is similar to that of the H-alpha profile of an associated flare.

Y yellow line A coronal emission line at It identifies the hottest regions of the corona. Z component of the geomagnetic field See geomagnetic elements. Zeeman effect The splitting of some solar spectral emission lines due to the presence of a strong magnetic field.

Briefly, the lines split into three or more components of characteristic polarization. The components are circular if the local magnetic field is parallel to the line of sight, and linear if the field is perpendicular to the line of sight. The amount of splitting is proportional to the strength of the field. Zurich sunspot classification See sunspot classification. Zurich sunspot number See sunspot number. A daily and half-daily index of geomagnetic activity determined from the k indices scaled at two nearly antipodal stations at invariant magnetic latitude 50 degrees Hartland, England, and Canberra, Australia.

In spectroscopy, and in particular the solar Fraunhofer spectrum, a characteristic wavelength of emitted radiation that is partially absorbed by the medium between the source and the observer.

A range of heliographic longitudes in either the northern or southern solar hemisphere seldom both at the same time containing one or more large and complex active regions formed by the frequent, localized emergence of new magnetic flux.

A portion of the solar limb displaying active prominences; typically associated with an active region. A localized, transient volume of the solar atmosphere in which plages, sunspots, faculae, flares, etc. An active region that exhibits a group or series of spike- like surges that rise no higher than 0. A geomagnetic index of the auroral electrojet, which characterizes the maximum range of excursion both positive and negative from quiet levels; measured at a given universal time by using the combined data from a worldwide ring of high-latitude magnetic observatories.

A daily index of geomagnetic activity for a specific station or network of stations represented generically here by k derived as the average of the eight 3-hourly ak indices.

And if Kp is currently elevated due to a phenomena called corotating or stream interaction, then be on the lookout for elevated Kp and potential for auroral viewing 27 days or one solar rotation from now. You can also check the predicted Kp in the next few days with this website , but without the graphic. The Kp Index bar plot shows geomagnetic activity for eight 3-hour periods per day. The higher the bars, the higher the activity.

Bars in red have a Kp over 4, indicating a better chance of aurora activity. The final step in making your aurora prediction complete is knowing the best geographic location for viewing. In general, you are more likely to see an aurora at a higher latitude, closer to the North or South Poles.

Simple, right? Well, not exactly. For aurora viewing, the magnetic poles are more important. Luckily, SWPC has developed a handy table that lists many major cities and their corresponding magnetic latitude see table below.

Therefore, an azimuth of this arc with respect to the local geographic meridian which is also the great-circle arc, connecting the station and the corresponding geographic pole is our "meridian" angle: positive to East from the North geographic meridian and positive to West from the South geographic meridian.

According to the definition of geomagnetic coordinates under the dipole approximation, the magnetic local time MLT is measured by the flare angle formed by two planes: the dipole meridional plane, which contains a subsolar point on the Earth's or any altitude surface, and the dipole meridional plane which contains a given point on the surface that is, the local dipole meridian. This definition cannot be applied to the CGM coordinate system because the latter is non-orthogonal and the CGM meridians do not cross the magnetic equator elsewhere [cf.

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