Field-Aligned Dependant Propagation A Program for the Assessment of E-layer Field-Aligned Propagation Version 1.01 - May 1995 James M. Roop, K0BI 1. INTRODUCTION 1.1 FLD-ALGN is a graphical field-aligned propagation analysis program that aides in the determination of possible auroral scatter and Field-Aligned Irregularity (FAI) propagation paths. The program will "paint" the area bound by the aurora boundary ellipse for a specified station location for all possible auroral scattering locations. Another option will show locations that can typically be worked by auroral scatter for a given K-index. For FAI propagation, the program will display all possible scattering locations that will provide FAI propagation between two specified locations as well a plotting isoflection loci for a specified scattering location. 1.2 Station location is entered by "clicking" a location with a mouse. Location information may also be entered by manually entering the locations Maidenhead grid square. 1.3 FLD-ALGN is based on the work of several articles that have appeared in QST. These articles include Richard Miller,"Radio Aurora", QST, January 1985; Emil Pocock, "Practical Radio Aurora", QST, March 1990; and Thomas F Kneisel, "Ionospheric Scatter by Field-Aligned Irregularities at 144 MHz", QST, January 1982. These and other article are also found in "Beyond Line of Sight, A History of VHF Propagation from the Pages of QST', Emil Pocock, editor, ARRL (1992). Another reference is Radio Auroras, Charlie Newton, G2FKZ (RSGB, 1991). 1.4 The program FLD-ALGN is copyrighted with all rights reserved by the author. However, the unregistered version of FLD-ALGN, version 1.01 may be freely used. The program may also freely distributed as long as no profits are realized. Versions of FLD-ALGN that are registered to a specific person may not be distributed. 2. SYSTEM REQUIREMENTS 2.1 CPU requirements: A 286 or better system is required. A math coprocessor is required for satisfactory performance. Dismal performance will occur with anything less than a 486DX. 2.2 Monitor requirement: Minimum requirements are an EGA monitor and display adaptor. 2.3 A Microsoft compatible mouse is required for full functionality. 3. STARTING THE PROGRAM 3.1 The following files are required for FLD-ALGN version 1.01: FLD-ALGN.EXE the program executable MAP.ESP map image file MAGDIPV2.DAT geomagnetic field (dip latitude) data 3.2 Generally, the program files should be in the same sub- directory. To start the program, change directory to the appropriate sub-directory and enter: FLD-ALGN 3.3 Map files, other than the default MAP.ESP, may be selected from the command line by entering, for example: FLD-ALGN CAN-USA.ESP 3.3.1 Map files for ES-PROP version 1.4 are usable with FLD- ALGN. However, FLD-ALGN is only usable for CONUS and adjacent areas (southern Canada, northern Mexico and the Caribbean. 4. PROGRAM OVERVIEW 4.1 Program options are selected by the function keys. A menu is displayed listing the program options. Location data is with the mouse by default when a mouse is detected. Optional keyboard entry may be toggled by entering the letter "k" when the menu is displayed. The message "kybd" appears below the lower right corner of the map to indicate keyboard entry. 4.2 [F1] Plot Isoflection Loci Plots isoflection loci (lines of equal reflection angle from the scatterer) for a given scattering location. See T. Kneisel, "Ionospheric Scatter by Field-Aligned Irregularities at 144 MHz". FLD-ALGN plots contours similar to those shown in figure 3 of Kneisel's article. 4.2.1 An arc (in white) will be displayed representing the loci of possible FAI propagation path endpoints if the user location has been set and within range of the scattering location. See 4.8 for details on setting the user location. 4.3 [F2] FAI Path Analysis Path endpoints are entered by using either the mouse or the keyboard. If the two locations do not exceed the maximum distance for E-layer propagation, then all possible scattering location that are within range of either station are evaluated. This exhaustive process is very computational intensive and requires a math coprocessor for satisfactory performance. 4.3.1 At each point that is evaluated, the reflection angle to both of the path endpoint locations is evaluated. For a scattering location to support propagation between the two path endpoints, the sum of the reflection angles to the two path endpoints must be equal to zero. Since scattering locations are evaluated at discreet intervals of latitude and longitude, the likelihood of evaluating a location where the angles sum to exactly zero is low. The program will plot a point if the sum of the angles is less than .75ø. Points where the sum of the angles is less than .25ø are plotted in red, whereas points where the sum of the angles is greater than .25ø (but less than .75ø) are plotted in blue. 4.3.2 The time required to evaluate all points will be in excess of one-half hour when the program is run on a 486SX/25. 4.3.3 Scattering location evaluation can be ended by entering [F10] 4.3.4 After all the scattering locations have been evaluated (or the evaluation process interrupted as described in 4.3.3) specific scattering locations can be evaluated by pointing to the scattering location with the mouse. If the left mouse button is clicked on valid scattering location, the program will display the azimuth and elevation angles to the scattering location from each of the path endpoints. To exit this mode and return to the main menu, enter [F10] or click the right mouse button. 4.4 [F3] Aurora Boundary Ellipse FLD-ALGN plots isoflection loci for all possible scattering locations within range of an entered location. The set of overlapping loci will define an area whose perimeter is known as the boundary ellipse (see E. Pocock, "Practical Radio Aurora"). The area that is displayed on the map by FLD-ALGN represents the area within which auroral scatter communications can be made. 4.4.1 If a user location has be set (see 4.8), FLD-ALGN will use that location , otherwise the user will be prompted to enter a location. 4.4.2 Aurora boundary ellipses can be inferred for any location entered on the map. The areas that are displayed represent the best-case conditions where the auroral front will extend far enough south relative to the location of the entered station location. From figure 4 in Miller, "Radio Aurora", it can be see that there are only 1.3 auroras per year at a geomagnetic latitude of 52ø compared to 97 auroras per year for a geomagnetic latitude of 60ø. Therefore, the auroral front will extend below 52ø magnetic latitude less than 1% of the time for when aurora conditions will exist in the southern provinces of Canada. FLD-ALGN will display in blue those areas where to which auroral propagation is likely to exist less than 1% of the time. Areas where auroral propagation is more likely to exist will be displayed in magenta. 4.4.3 [F10] will interrupt the aurora boundary ellipse evaluation process and re-display the menu. 4.4.4 FLD-ALGN attempts to evaluate the speed of the computer system and will evaluate fewer scattering locations for slower systems. This is done in order to reduce the amount of time it takes to evaluate the auroral propagation area for a given location. 4.5 [F4] Auroral Paths for a Specified K-index FLD-ALGN determines all possible scattering locations at a specific magnetic latitude that is determined from the K-index. The isoflection loci are plotted for scattering locations within range of an entered location. During magnetic storms, the auroral oval expands and moves southward. The greater the intensity of the geomagnetic strom (an hence the K-index) the further south the auroral oval moves. The magnetic latitude that FLD-ALGN uses for a given K-index was determined using figure 8 of Richard Miller's article Radio Aurora in conjunction with a map displaying geomagnetic dip latitude (such as figure 2 in Emil Pocock's Practical Radio Aurora.) 4.5.1 If a user location has be set (see 4.8), FLD-ALGN will use that location , otherwise the user will be prompted to enter a location. 4.6 [F5] Clear Map The map is erased and a new map is displayed. 4.7 [F6] Create PCX Graphic of Map Registered copies of FLD-ALGN have the ability to create PCX format graphic files of the map. The PCX format graphics files can be viewed by a number of graphics programs including Windows' Paintbrush. Users of slower computers may find it useful to save the map image for future reference instead of having to regenerate the map. 4.8 [F7] Set User Location This option permits the user to set a location that will used in subsequent operations as described in sections 4.2, 4.4 and 4.5. If a user location was not set, then the user will be prompted to enter a location for those options. 4.8.1 The user location can be changed by entering a new location. 4.8.2 The user location can be cleared by clicking the right mouse button (or entering a null entry if entering by keyboard.) 4.9 [F8] Adjust Scattering Point Height The height at which auroral scattering is evaluated can be toggled the [F5] key. Heights between 90 and 120 km can be selected. The scattering height should be set before evaluation of FAI paths or auroral boundary ellipses. Maximum distances for auroral propagation appear to occur at lower scattering heights, i.e., 90 km. 4.8 [F10] End Program. [F10] terminate the program when the menu is displayed, otherwise, the evaluation in progress is interrupted and the menu is redisplayed.