Description of the Current Ionospheric Map
IMPORTANT: To obtain the latest maps please refresh the page content periodically or click here for the automatically updated display.
The UAF EPPIM model forecasting runs have been continued on a semi-permanent basis starting from April 1997. Duration of each run is choosen as thirty days. The run "cold re-start" takes up to 8-10 hours --on averege, 4-6 hours --for the model to converge from the initial conditions (VSH model). During this time the maps are marked by the "COLD START" lable.
The forecasts of the electron density distribution and the drift velocities are updated at every model time step (5 minutes). The current run resolution is 30x30 km for the horizontal cell size and 10 km for the altitude step. SGI Octane workstation in fully dedicated mode provides computational resources for the run, while the WWW-hadling is supported by the ARSC Web server.
The ionospheric maps are cut from the 3-D domain of UAF EPPIM northward from 50N latitude (GEOGRAPHIC LATITUDE-LOCAL TIME frame) at altitude of 300 km. For two time instants --the current UT (upper row) and UT + the forecast advance time (lower row)-- the maps show the electron density contours and the vectors of ionospheric drifts. The forecast advance time is defined as a distance to ACE satellite devided by the current solar wind velocity (see Introduction for details). The electron density is represented in accordance with the specified color code (note the logarithmic scale). Small white numbers inside the color bar indicate the corresponding plasma frequencies in MHz, derived from the relation
Ne [cm -3] = 1.24*104 * (foF2 [MHz] ) 2
Since the cross-section altitude of 300 km is relatively close to the F2-region maximum, these values can be useful for a crude evaluation of the foF2 range.
The left panel in each row shows a general view of the electron density distribution and the current values of geophysical indeces, which are obtained from the Space Environment Center WWW-sites. The real-time Air Force/NOAA nowcast of the geomagnetic activity is shown on the plot left side and the current level of solar activity is specified on the plot at the bottom. The orientation and magnitude of the ACE IMF vector are placed on the graph in the lower left corner. During short periods without IMF inputs (currently, the occasional gaps in ACE real-time data rarely exceed a few hours per week of observations), the model adopts the last available IMF values for Bx, By, and Bz, superimposed with sinusoidal fluctuations with amplitude of 1 nT and a period of one hour. The IMF data gaps are indicated by the white color of the plotted IMF vector. The arrow in the lower right corner represents a scale for the drift magnitude of 1.5 km/sec. The date and time are present in the upper right corner of the left panel. The right panel at each row shows the maginified ionospheric map. In both cases the continent map in Equdistant Azimuthal Projection is superimposed with the ionospheric density contours.
Convenience of the adopted for this display GEOGRAPHIC LATITUDE-LOCAL TIME frame allows for positioning of the local noon (upper side of the plot), local midnight (lower side), and, correspondingly, the local morning (right) and evening (left) at the permanent locations, independently of the Earth rotation. Instead, in this frame the Earth's rotation is represented by the counter-clockwise rotation of the continent contours, shown from the steady view point above the geographic North Pole (center of the plot).
In this frame the solar terminator line --or the boundary between day and night produced by the shadow of spherical Earth-- crosses the field of view horizontally. Its exact location depends on the season. During the winter solstice (December 22nd), the terminator is in the upper third of the frame, tangential to the latitude circle of 66.7N (Polar Circle). Thus, the area inside this circle of 66.7N is always on the dark side, which represents the conditions of extended polar night for the region. By contrast, during the summer solstice (June 22nd), the terminator is located in the lower third of the frame, again tangential to the Polar Circle but this time inclusively. The region inside the Polar Circle is always on the day-side during the summer season, which is known as extended polar day phenomena. Position of the terminator for the Spring (March 22nd) and the Autumn (September 22nd) equinoxes divides the frame exactly in half.
The terminator location is critical for formation of the polar ionosphere. Solar extreme ultra-violet (EUV) radiation in the range 50-1026 Angstrom or 5-103 nm ionizes the upper atmosphere on the day side. This process dominates in formation of the day-side ionosphere. Long-living atomic oxygen ions (O+, being produced on the day side, co-rotate with the Earth and form a tail of ionization in the evening sector. These structures are superimposed with precipitation of the energetic particles in the auroral zone, also causing ionization of the upper atmosphere. The auroral zone forms an oval centered around the Geomagnetic Pole, which is situated to the West from the Greenland northern part. In the geographic frame the center of auroral oval precesses together with geomagnetic pole around the geographic North Pole. Thus, in this frame the auroral oval exact location varies during the day course resulting in numerous phenomena collectively called UT-effects. Their common feature is a non-symmetric with respect to the local time behavior of ionospheric parameters.
Ionospheric dynamics significantly complicates the picture. The presence of noticeable electric field in the polar region results in the ionospheric plasma drifts in the crossed magnetic and electric fields (ExB-drift). Typical value of electric field at 50 mV/m corresponds to the drift velocity of 1 km/sec. Both values increase during the disturbed periods up to 100-150 mV/m or 2-3 km/sec respectively.
The ExB-drift pattern often consists of two cells with the anti-solar drift direction in the pattern center. Due to resemblance to the thermal convection pattern, this motion often called ionospheric convection. As in the case of auroral precipitation, the convection pattern is centered around the Geomagnetic Pole and precesses around geographic North Pole during the course of the day. The convection pattern is contolled by the Interplanetary Magnetic Field (IMF), especially ts vertical component Bz. IMF is the magnetic field "frozen" into propagating parcels of the solar wind and is highly variable in time. All these factors determine distribution of the ionospheric parameters and their variability. Available on this page animated ionospheric maps show the dynamics of the polar ionosphere in a time-dependent fashion. To illustrate the polar ionosphere variability during highly disturbed periods, an example of the ionospheric animation during the period of magnetic storm of March 20-21, 1990 is also available on-line.
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