Equatorial Spread F(ESF) intensity
quantification from ionograms
M. A. Abdu1 , I. S. Batista1, B. W. Reinisch 2,
J. W. MacDougall3, J. H. A. Sobral1
1Instituto
Nacional de Pesquisas Espaciais, Sao Jose dos Campos, Brazil.
[email protected]
2Center for Atmospheric Research, University of Massachusetts,600 Suffolk
Street, Lowell, MA, USA
3 Department of Electrical Engineering, University Western Ontario, London,
Ont., Canada N6A 5B9
 Ionosondes are widely used in the investigation of the ESF, and
therefore a quantitative assessment of the intensity of an ESF
event from ionograms is an important question;
 The degree of range spreading of the F layer trace has been
widely used as a very approximate index of the event intensity
in such a way that the index numbers 1, 2 and 3 indicate, weak,
medium and strong events, that corresponds to range
spreading <100 km, >100 km <200 km and > 200 km
respectively.
 Here we present and discuss what appears to be a more precise
and practical way to quantify the ESF intensity, and it is based
on the maximum frequency back-scattered by the irregularities
and that is registered in the ionogram as fop.
Chapagain et al-2009
Abdu and Brum, 2009 EPS
Relationship between spread range and fop
COPEX Sites
& SL, Fz, CP
15
10
o
30 N
5
LATITUDE
-5
-10
Boa Vista
o
20 N
0
SL
o
10 N
r
uato
q
E
Dip
JIC
-15
FZ
Cachimbo
o
10 S
-20
Campo Grande
o
20 S
-25
CP
30 S
o
-30
o
S
40
-35
-80
-75
-70
-65
-60
-55
-50
LONGITUDE
-45
-40
-35
-30
SAO LUIS, BRAZIL
Monthly averaged Spread F Distribution
in terms of fop, the top frequency of the spread F trace
for the year 2002-2003
12
10
8
6
4
2
0
12
10
8
6
4
2
0
12
10
8
6
4
2
0
12
10
8
6
4
2
0
Monthly averaged Spread F Distribution
in terms of the Spread Range in KM
for the year 2002-2003
SAO LUIS
250
Jul. 2002
Aug.
Sep.
200
July 2002
Aug
Sep
150
100
50
0
KM
Oct.
Nov
Dec.
200
00 03 06 09 12 15 18 21 24 00 03 06 09 12 15 18 21 24
00 03 06 09 12 15 18 21 24
Oct
Nov
Dec
150
100
50
0
250
Jan. 2003
Feb.
Mar.
200
00 03 06 09 12 15 18 21 24 00 03 06 09 12 15 18 21 24 00 03 06 09 12 15 18 21 24
Jan 2003
Feb
Mar
150
100
50
0
00 03 06 09 12 15 18 21 24 00 03 06 09 12 15 18 21 24 00 03 06 09 12 15 18 21 24
KM
Apr.
May
Jun.2003
200
Apr
May
Jun 2003
150
100
50
00 03 06 09 12 15 18 21UT 00 03 06 09 12 15 18 21 UT 00 03 06 09 12 15 18 21 UT
0
00 03 06 09 12 15 18 21 LT 00 03 06 09 12 15 18 21 LT 00 03 06 09 12 15 18 21 LT
250
SAO LUIS, 2002-03
Spread Range (KM)
200
150
100
50
Equation
y = a + b*
Adj. R-Squar 0.98435
0
0301h'p
0301h'p
0
2
4
Intercept
Slope
Value
Standard Erro
-1.5752
1.28609
18.659
0.24139
6
fop (MHz)
8
K
h'p
0209h'p
0210h'p
0211h'p
0212h'p
0301h'p
0302h'p
0303h'p
0304h'p
0305h'p
0306h'p
0307h'p
Linear Fit of 0301h'p
10
12
250
SAO LUIS, 2002-03
150
100
K
h'p
0209h'p
0210h'p
0211h'p
0212h'p
0301h'p
0302h'p
0303h'p
0304h'p
0305h'p
0306h'p
0307h'p
Linear Fit of 0301h'p
50
Equation
y = a + b*
Adj. R-Squar 0.98435
0
0301h'p
0301h'p
Intercept
Slope
Value
Standard Erro
-1.5752
1.28609
18.659
0.24139
250
0
2
4
6
fop (MHz)
8
10
12
There is higher
probability of intense
events
when the occurrence is
more frequent
SL - 07/2002 - 06/2003
0207
0208
0209
0210
0211
0212
0301
0302
0303
0304
0305
0306
200
Spread F range (km)
Spread Range (KM)
200
150
100
50
0
-10
0
10
20
30
40
50
60
70
80
Monthly SF Occurrence Percentage (%)
90
100
110
RESULTS FROM CONJUGTE POINT
OBSERVATIONS
350
300
Cachimbo
All days
250
h`P
200
150
100
50
Equation
y = a + b*x
Adj. R-Square
0.32452
Value
h`P
Intercept
h`P
Slope
Standard Error
-5.02237
5.08362
16.2918
0.51096
0
2
4
6
8
10
12
14
16
18
20
foP
350
350
BOA VISTA
300
250
250
200
200
h`P
h`P
300
150
100
CAMPO GRANDE
150
100
50
Equation
y = a + b*x
Adj. R-Square
0.4435
h`P
h`P
Intercept
Slope
Value
Standard Error
25.1258
5.44391
6.64726
0.26015
50
0
Equation
Adj. R-Square
y = a + b*x
0.40327
h`P
h`P
Intercept
Slope
Value
Standard Error
23.58915
3.30501
5.17468
0.15889
0
0
5
10
15
foP
20
25
30
0
5
10
15
foP
20
25
30
Linear Fit of h`P-Spread Fange (KM)
220
COPEX 2002
200
BV
180
160
140
CX
120
100
CG
80
60
40
20
0
5
10
15
fop
20
25
MHz
 For a given spread range the fop is larger over low latitude
than near the equator. This means that the irregularities
grow more intense over low latitude than over dip equator.
 There is an asymmetry between the conjugate sites.
Abdu et al., 2009
Conclusions
 Ionogram signature of the ESF/plasma bubble
irregularities can provide a quantification of the event
intensity;
 Coherent back-scattering is an important component of
signal returns constituting spread F trace in equatorial
ionograms;
 The spread range increases with increase of the top
frequency of the irregularity trace;
 While the degree of range spreading (in km) is a
measure of the ESF intensity, it is less suitable as an
index of the ESF intensity than is the fop;
 The ESF irregularity growth is more intense over low
latitude than over the equatorial region;
 Hemispheric asymmetry exists in the irregularity
intensity due probably to local conditions favoring the
irregularity growth.