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.
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
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
and from there the right edge of box 2 is
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
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
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 email@example.com. This poster is available on-line at