The Variability in the Morning-Time Plasma
Density Irregularities Occurrence Patternin Mid-to-Low Latitude during the solar
minimum period
Seung Jun Oh1, Hyosub Kil2,Young-Sil Kwak3
and Tae-Yong Yang3
1 : SELab, Inc, Seoul, Korea, 2. JHU/APL, MD, USA, 3. KASI, Daejon, Korea

oh@spweather.com

ST-26-A014, AOGS, 2012 @Sentosa Resort world, Singapore

Motivation

A05302OTSUKA ET AL.: MSTID AND F-REGION FAIHUANG ET AL.: THE LONGITUDINAL EFFECT OF SPREAD F

A05302
RS1015

RS1015125.16E
87.58 E

RS1015HUANG ET AL.: THE LONGITUDINAL EFFECT OF SPREAD F

RS1015Figure 2. The occurrence percentage as a function of local time for Changchun and Urumqi,
Table 1. Geographic
andtheGeomagneticof the Two Stations
respectively,
during
10 yearsParameters(1992–2001).

Figure 7. Two-dimensional maps of the 630-nm airglow perturbations observed at Sakata, Japan,
between 0004 and 0202 LT on 17 June 2004. The airglow layer was assumed to exist at the altitude thatwas determined by the triangulation method. FAI echo intensity observed with the MU radar was projectedonto a surface of the airglow layer along the geomagnetic field lines. Two thick curves represent the mosteastward and westward beams (azimuth angles are %29! and 22!, respectively).

[Otsuka et al., 2009]•Geographic Longitude

Geographic Latitude

Geomagnetic Longitude

Geomagnetic Latitude

Changchun
Urumqi125°16′E
87°38′E

43°50′N
43°45′N

192°53′E
160°41′E

36°46′N
33°05′N

development of spread F at midlatitude [Kelley et al.,2004], and showed that factors such as neutral wind,
acoustic gravity waves (AGWs) and ambient electric field
were very important to influence the spread F occurrence[Dyson et al., 1995; Huang et al., 1994; Bowman, 1991,1990].
[4] Among the above researches, one of the striking
phenomena is the regional feature of spread F occurrence. It is known that there is an obvious longitudinal
effect of spread F occurrence both in the equatorial
regions and midlatitudes [Earle et al., 2006; Mwene et al.,
2004; Abdu et al., 1992; Batista et al., 1986]. Similar study
on the Asian sector was also conducted by Igarashi andKato [1993]. It is important to study the causes of longitudinal effects of spread F occurrence in order to better
understand the factors affecting the spread F occurrence.
[5] As a case study, this paper is aiming at presenting
some new observational findings of longitudinal effectsof spread F using ionosonde data from two Chinesestations. These stations have almost exactly the samegeographic latitudes but with a significant difference oflongitude. In particular, there is a sharp contrast of theground conditions of these two stations. One of them(Changchun Station) is along China’s coast, near the vast
ocean, while the other (Urumqi Station) is in the very
center of Euro‐Asian continent. There have been dis-tabulated form based on the traditional ionograms are
suffixed with different letters to indicate observational
conditions. Suffixed letter “F” or “Q” represents spread
F occurred at that hour. In our statistics, this is counted
as one time of spread F occurrence and it enters into ourdatabase for further analysis as outlined here. Each individual occurrence was summed up for 1 whole day toobtain the total number of occurrences (or daily numberof occurrence) to make daily, monthly and yearly statistics. For the convenience of comparison, the term
“occurrence percentage” is used in some figures and thisis a measure of the frequency with which the spread F has
occurred at a particular hour. In other words, it is a ratioof the times of occurrence at a particular hour to the total
possible counts of that hour during a given period(1 month or years). Table 1 shows the geographic andgeomagnetic parameters for the two stations.

[Huang et al., 2011]

The plasma density irregularities appear in the nighttime midlatitude
ionosphere, and it is suggested that it is relevant to the MSTIDs’ depletion
regionObservations and Results of Analysis
The plasma irregularities occurs in the midlatitude during the3. morning
time aswell and its occurrence probabilities are different with respect to the longitude.

the MU radar on the night of 16 June 2004. The Doppler
velocity was obtained from the first-order moment of theecho spectrum. A positive (negative) value of the Doppler
velocity represents motion away from (toward) the radar.
It should be noted that the small regions of large negative
Doppler velocity (shown by blue color) at an altitude of400 km at 0050 LT on the beam with an azimuth of 0!
(Figure 8, top) and at an altitude of 380 km at 0040 LT on
the beam with an azimuth of 10! (Figure 8, middle) were
due to the aliasing of the Doppler spectrum because the FAI
Doppler velocities exceeded the spectral window of thisobservational mode (±224 m/s). From a comparison with
the SNR of FAIs shown in Figure 2, it is found that thebloblike FAI regions have positive (upward/northward)
Doppler velocity and that the downwelling FAI regions havenegative (downward/southward) Doppler velocity.
[14] The amplitude of the Doppler velocity perturbations
decreased with a positive change in the azimuthal directionof the radar beams from the north (an azimuth of 0!) to the•Stations

FAIs by Otsuka et al. [2007]. Line-of-sight Doppler velocities in each beam were averaged over an altitude range from
200 to 550 km, and the data with SNR less than 0 dB wereexcluded in this procedure in order to reduce the estimation
errors. The amplitude of the line-of-sight velocity perturbations on the radar beams with an azimuth of 0!, 10!, and 22!
at 0000– 0200 LT were 78, 69, and 65 m/s, respectively.
Here, we assumed that the line-of-sight velocities oscillated
symmetrically between positive and negative directions. By
using the eastward and northward components of the amplitude of the FAI velocity perturbations (vx and vy, respectively)
in a plane normal to the geomagnetic field line, we could
describe the line-of-sight component of the FAI velocity
perturbation (Vi) for each beam direction (i), as follows:
Vi ¼ ðvx sin ai þ vy cos ai Þ;ð1Þ

where ai is the azimuth angle for each beam direction (i). vx
and v were determined in the least squares fitting method[7] Figure 1 is the daily number of spread F occurrences at the two stations and some corresponding geophysical parameters for the 10 years. It is seen obviouslythat on the years when solar 10.7 fluxes are low (roughly
from 1994 to early 1999), the occurrences at both stations
are high, thus showing a negative correlation betweenMorning time plasma irregularities
occurrence in low-to-mid latitude duringsolar minimum?

Analysis• Observation : in-situ measurements by DMSP (Defense•••Meteorological Satellite Program) F13 with sun-synchronousorbit at 800 km altitude
Data : 0600 LT (morning sector) data during 2006-2009
Quality control : The rejection of the sudden peaked data thathave 20% larger electron density than the 400 sec average
electron density.
Irregularities detection : The percentage standard deviation ofthe 40 sec data normalized by the mean plasma density withthe threshold of 5% has been used to detect irregularities.

VHF	  (40.8	  MHz)	  radar	  observa5ons	  –	  irregulari(es	  (~3	  m)

Ni

Ni

Ni

Detection
10000

10000

DOY : 07246

DOY : 07246

DOY : 07245
108886threshold

46threshold

4

STDDEV/Ni(%)

10
STDDEV/Ni(%)

106

2060

060

060

40

40

40

0-20-40

Mag. Latitude (o)220200-20-40

200-20-40-60-60-60
44445.83•104 5.84•104 5.85•104 5.86•104 5.87•104 5.88•104 5.89•104 5.90•107.58•10
7.60•104 7.62•104 7.64•104 7.66•104 7.68•104 7.70•104 7.72•106.50•10Second of the day
Second of the day

mid-latitude irregularities

threshold

42

Mag. Latitude (o)Mag. Latitude (o)STDDEV/Ni(%)

10000

density depletions

6.52•104

6.54•104
6.56•104
Second of the day

6.58•104

blobs

The examples of irregularities detection results during solar
minimum

6.60•104

s/l distribution

autumn equinox

20

20

100-10-20-30
30

Mag. Latiitude (o)Mag. Latiitude (o)

30

30

060

120

summer180solstice
o240

300

10Occurrence Probability(%)

0-100102030-20-30060120180
Longitude (o)

240

300

Occurrence Probability(%)
010203600-10-20-306012030

Longitude ( )20100360
Mag. Latiitude (o)Mag. Latiitude (o)spring equinox

winter180
solstice
Longitude (o)

240

300

360

300

360

2010

Occurrence Probability(%)

0-100102030-20-30060120180
Longitude (o)240

Occurrence Probability(%)
30

0102030The seasonal-longitudinal distribution of the irregularity occurrence
rate during Spring equinox (Mar., Apr. and May), Summer solstice (June,
July and Aug.), Autumn equinox (Sep., Oct. and Nov.), and Wintersolstice (Dec., Jan., and Feb). The plots show the average occurrence
rate obtained from the F13 0600 LT data during 2007-2009.

latitudinal distribution
summer solstice30

2020
Mag. Latitude (o)Mag. Latitude (o)spring equinox
30

100
ï100
ï10ï20ï20
ï300

1051015
20
Occurrence Probability(%)ï30025

5autumn equinox
30

2020

10

Mag. Latitude (o)Mag. Latitude (o)25winter solstice300ï10ï20
ï300101520
Occurrence Probability(%)

100ï10ï205101520
Occurrence Probability(%)

25

ï30
0

5101520
Occurrence Probability(%)

25

The latitudinal distribution of the longitudinal averageirregularity occurrence rate during 2007-2009.

plasma density vs. occurrence rate20

20

100-10-20
-30
060

120

summer180
solsticeo

240

300

360

Longitude ( )3020
10Log Ni

0-10

3.6

3.7

3.8

3.9

4.0

4.1

4.2

-20-30
060

120

180
Longitude (o)240

Log Ni
3.6

3.7

3.8

3.9

100-10-20-30
30Mag. Latiitude (o)Mag. Latiitude (o)spring equinox
30
Mag. Latiitude (o)Mag. Latiitude (o)spring equinox
30300

360

060120summer
180solsticeLongitude (o)

240

300

360

300

360

2010

Occurrence Probability(%)

0-100102030-20-30
060

120

180
Longitude (o)240

Occurrence Probability(%)
4.0

4.1

4.2

0

102030The seasonal-longitudinal distribution of the average plasma
density during 2007-2009(Left). The irregularity occurrence
rate is likely to be anti-correlated with the background plasma
density especially during spring and summer.

The annual variation of theoccurrence probabilities from2006 to 2009

Magnetic Latitude (o)200630
2010spring

0-10-20-30
30
2010summer0

Magnetic Latitude (o)-10-20-3030
20
10autumn

0-10-20-3030
20100winter-10-20-30060

120180240oGeographic Longitude ( )300

Occurrence Probability(%)
0918273645360

Magnetic Latitude (o)

2007
30
20
100-10-20-30
30
20
100

Magnetic Latitude (o)-10-20-3030
20100-10-20-3030
20
100-10-20-30
060

120180240
Geographic Longitude (o)300

Occurrence Probability(%)
0918273645360

Magnetic Latitude (o)20083020100-10-20-30
30
20100

Magnetic Latitude (o)-10-20-3030
20100-10-20-3030
20
100-10-20-30060120180240
oGeographic Longitude ( )300

Occurrence Probability(%)
0918273645360

Magnetic Latitude (o)

2009
30
20
100-10-20-30
30
20100

Magnetic Latitude (o)-10-20-3030
20100-10-20-3030
20
100-10-20-30
060120180240
oGeographic Longitude ( )300

Occurrence Probability(%)
0918273645360

The annual variation of theoccurrence probabilities from2006 to 2009
The seasonal-longitudinal variation of the irregularity
occurrence rate between 2006 and 2009. Spring equinox,
Summer solstice, Autumn equinox and Winter solstice from
top to bottom. Similar distribution repeats year after year.
However, the occurrence rate increases with year (with thedecrease in solar flux).

Comparison	  of	  the	  E-­‐and	  F-­‐region	  irregularity	  distribu5ons

Comparison	  with	  COSMIC	  dataThe	  echoes	  or	  the	  ﬁeld-­‐aligned-­‐irregulari(es	  are	  seen	  to	  occur	  near	  F-­‐peak	  height[Courtesy	  of	  Wookyoung	  Lee,	  UCAR,	  USA]

The	  Signature	  of	  the	  morning	  5me	  irregulari5es	  observed	  by	  VHF	  radar	  in	  Korea

18

The	  Signature	  of	  the	  morning	  5me	  irregulari5es	  observed	  by	  VHF	  radar	  in	  Korea

19

The	  Signature	  of	  the	  morning	  5me	  irregulari5es	  observed	  by	  VHF	  radar	  in	  Korea

20

The	  Signature	  of	  the	  morning	  5me	  irregulari5es	  observed	  by	  VHF	  radar	  in	  Korea21

SummaryWe have investigated the plasma density irregularities at 0600 LT by analyzing theDMSP F13 data during 2006-2009 and VHF radar images during 2010-2012• The irregularity occurrence rate in midlatitudes is greater than that in the equatorial
region during the morning time. The VHF radar observation in Korea shows the signatureof the morning -time irregularities in mid-latitude.
•The irregularity occurrence rate in the winter hemisphere is greater than that in thesummer hemisphere. The irregularity occurrence rate is likely to be anti-correlated withthe background plasma density whereas the radar echos observed in mid-latitude are seen
to occur near F-peak height. These behaviors are similar to that of the plasma blobdistribution.
•The linkage of Es with the irregularity occurrences was not clearly seen based on theclimatological studies of VHF radar data.
• The onset conditions and growth rate of instabilities in the morning time and the causal
link of well-known phenomena such as TID and Es with the mid-latitude irregularities areSTILL REMAINING QUESTIONABLE.

Thank you