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					                                                                                                 MIDLATITUDE SPREAD F
                                                                                                    P.         Bhaneja1,                                        G. D.   Earle 1,       R. L.        Bishop2

                                                   (1) William. B. Hanson Center for Space Sciences, University of Texas at Dallas, (2) AeroSpace Corp.


ABSTRACT                                                            PROGRAM EXPLANATION                                                                                                                                                     FUTURE WORK
This research involves a case study of Midlatitude Spread F         An autonomous computer algorithm has been developed to                                                                                                                  •Correlation between various geophysical indices and MSF
(MSF) at Wallops Island (37.8°N, 75.5°W) using ionosonde            identify range and frequency MSF. Figure 3 shows how the                                                                                                                 will be studied.
                                                                                                                                                                                                                    FIGURE 6. The plot
data. Software has been developed in MATLAB to detect the           ionograms are processed and figure 4 shows a flow chart                                                                                                                 •Correlation between sporadic E and midlatitude
                                                                                                                                                                                                                    shows the percentage
edges of the O-Mode traces, so that range and frequency             describing the algorithm.                                                                                                                                                spread F is also to be investigated.
                                                                                                                                                                                                                    of spread days in
spreading can be objectively identified. A separate algorithm is                                                                                                                                                                            •A sample plot with all the indices, spread duration, time and
                                                                                                                                                                                                                    each month for the
used to identify sporadic E conditions. The intent is to                                                                                                                                                                                     sporadic E is shown in figure 10.
                                                                                                                                                                                                                    year 2002.
determine the seasonal variation of MSF over a complete solar                                                                                                                                                                               •Future work will involve assimilating the data from all
cycle from 1995-2005. The correlation between MSF and                                                                                                                                                                                        months in 1995-2005 into plots like that shown in
geophysical parameters such as, Kp, Ap, DST, Bz, F10.7 and                                                                                                                                                                                   figure 10.
sunspot number, and between sporadic E and MSF is to be                                                                                                                                                                                     •A booklet with collection of these plots will form the basis of
determined. An initial study using data from 2001-2004                                                                                                                                                                                       further research on obtaining a statistical analysis of
                                                                                                                                                                                                                    FIGURE 7. The plot       midlatitude spread F over Wallops Island, and may reveal
indicates that MSF occurs most frequently over Wallops Island
                                                                                                                                                                                                                    shows the percentage     seasonal and solar cycle-related trends.
in the autumn months.
                                                                                                                                                                                                                    of spread days for
                                                                                                                                                                                                                    months of Jan-Aug
INTRODUCTION
                                                                                                                                                                                                                    for the year 2003.
Ionospheric irregularities are temporal and spatial variations of
                                                                    FIGURE 3. Midlatitude Spread F event. The plot shows
the electron density lasting from a couple minutes to a few
                                                                    the boxes drawn to help identify both range spread (box
hours. In the lower latitudes of the F region of the ionosphere,
                                                                    1) and frequency spread (box 2).
these irregularities are called Equatorial Spread F. Occurrence
of similar irregularities in the midlatitude F region is also                                                Raw Ionogram Data.

called spread F, but at the midlatitudes the mechanism of                                                                                                                                                           FIGURE 8. The plot
formation of spread F is not well understood. Gravity waves                                                 Extract O-Mode Trace.
                                                                                                                                                                                                                    shows the percentage
are widely recognized as a potential cause of these density                                                                                                                                                         of spread days in
                                                                              Identify bottom edge of Box 1 by              Identify right edge of Box 2 by
perturbations in the F region. Ionograms obtained for spread F                counting the number of pixels at              counting the number of pixels at
                                                                                                                                                                                                                    each month for the
                                                                              each given altitude.                          each given frequency.
show thickness or spread in the F region in figure 1, which is                                                                                                                                                      year 2004.
significantly more than that obtained for a normal ionosphere           The pixels are compared to a threshold          The pixels are compared to a threshold
as shown in figure 2. The spread observed on the ionograms              and from there the bottom edge of box 1 is
                                                                        obtained.
                                                                                                                        and from there the right edge of box 2 is
                                                                                                                        obtained.
can be classified as range or frequency spread depending on
whether the signal is spread in range or frequency. This                The width of box 1 is fixed, 1.6 MHz to 3.5     The height of box 2 is fixed, 410 km to 530         •The weighted percent average for these four years is plotted
                                                                        MHz.                                            km.
corresponds to spread in depth and width respectively on an                                                                                                                  in figure 9.
ionogram.                                                               Count enhanced echoes within box 1.             Count enhanced echoes within box 2.

                                                                                                                                                                                                                                             FIGURE 10. Geophysical indices, spread occurrence,
                                                                        Compare to Spread F threshold set for           Compare to Spread F threshold set for
                                                                        range spread.                                   frequency spread.                                                                            FIGURE 9. The plot      duration, time and sporadic E are shown for one month
                                                                                                                                                                                                                     shows the weighted      (November 2004).
                                                                        Determine if range spread or not.               Determine if frequency spread or not.
                                                                                                                                                                                                                     percent average of
                                                                                                                                                                                                                     spread days in each    FUTURE EXPERIMENT DESCRIPTION
                                                                    FIGURE 4. Flowchart for the code that identifies spread                                                                                          month for the years    •A rocket launch will be conducted in the fall of 2006 to collect
                                                                    ionograms, identifying both range and frequency spread.                                                                                          2001 -2004.             data on midlatitude spread F and get more insight in this
                                                                                                                                                                                                                                             instability.
                                                                    DATA PRESENTATION                                                                                                                                                       •The experiment will have both ground based and rocket based
                                                                    •Data for four years (2001- 2004) have been collected and                                                                                                                measurements.
                                                                     plotted.                                                                                              DISCUSSION                                                       •This will collectively form a quantitative analysis of the F
 FIGURE 1. Midlatitude Spread F event for a 15 minute               •The percentage of MSF occurrence for each month of                                                    As shown in figures 5-9, there is substantial variability from    region radio propagation and TID environment with the in-situ
 sweep on 2 October, 2002. Only the O-Mode trace is                  available data for these four years is plotted and shown in                                                                                                             data giving a better picture and an in-depth look into the cause
                                                                                                                                                                           month to month and year to year in MSF occurrence. The fall
 shown.                                                              figures 5 through 8.                                                                                                                                                    of midlatitude spread F.
                                                                                                                                                                           season appears to have the highest incidence of MSF, which
                                                                    •A spreading event is classified as 1 or more ionograms with                                           may be related to the relationship between the local magnetic
                                                                     spreading evident, where 15 minutes is the normal                                                                                                                      WORKS CITED
                                                                                                                                                                           field and the nightime terminator [Earle et al., 2006]. A        1. Bowman, G.G., Short-Term Delays in the Occurrence of Mid-Latitude Ionospheric
                                                                     ionogram cadence.                                                                                     geometry in which these are aligned allows efficient electric       Disturbances Following Other Geophysical and Solar Events, J.Geomag. Geoelectr.,
                                                                                                                                                                                                                                              46, 297-309, 1994.
                                                                                                                                                                           field mapping between conjugate hemispheres, which may be        2. Cosgrove, R.B., and R.T. Tsunoda, Instability of the E-F coupled nighttime
                                                                                                                                                                           important to the generation of MSF. Alternatively, the high         midlatitide ionosphere, J. Geophys. Res., doi:10.1029/2003JA010243, 2004.
                                                                                                                                                                           incidence of thunderstorms in the spring and fall season at      3. Earle, G.D., A.M., Mwene, and J.P. McClure, A global study of nighttime
                                                                                                                                    FIGURE 5. The plot                                                                                         midlatitude topside spread echoes, submitted to J.Geophys. Res., 2006.
                                                                                                                                    shows the percentage                   Wallops Island may be related to enhanced MSF probabilities.
                                                                                                                                                                           Finally, [Bowman, 1994] has shown that MSF is more               ACKNOWLEDGMENTS
                                                                                                                                    of spread days for                                                                                      This research has been supported by NASA grant NNG04WC19G. The data for all
                                                                                                                                    months of Sep-Dec                      prevalent in periods with low F10.7 solar flux levels. This      the plots have been provided by NGDC, SPIDR and SPDF. We would also like to
                                                                                                                                    for the year 2001.                     correlation will be investigated in our future work, as will     thank Terry Bullett, Ray O Conkright, Rob Redmon for all their help.
 FIGURE 2. Same format as figure 1 for a normal                                                                                                                            correlations with sporadic E [Cosgroove & Tsunoda, 2004].
                                                                                                                                                                                                                                            FOR FURTHER INFORMATION
 quiescent ionosphere on the same night. Non-Spread                                                                                                                                                                                         Please contact pxb049000@utdallas.edu. This poster is available on-line at
 Event.                                                                                                                                                                                                                                     www.utdallas.edu/~pxb049000

				
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