Thermal Structure of the Topside Ionosphere at Low ... · at Low Latitudes: New Observational...
Transcript of Thermal Structure of the Topside Ionosphere at Low ... · at Low Latitudes: New Observational...
Thermal Structure of the Topside Ionosphere
at Low Latitudes:
New Observational Opportunities
Pei Chen Lai and William J. Burke
Boston College/Institute for Scientific Research
19 March 2014
Knowledge about the range of states that the topside ionosphere can assume and the conditions
that give rise to them is essential for improving existing models used in a host of practical and
research applications. Still, the topside is at best a partially explored region. Electron density
profiles (EDPs) acquired during COSMIC-GPS radio occultation events offer promise for fuller
views of the topside. However, their reliance on Abel inversions has given users pause.
This presentation proceeds in three stages: First, we review the physics and mathematical
techniques underlying EDP extractions during occultation intervals as well as the measurement
capabilities of other relevant in situ sensors. Second, recognizing that reliance on Abel inversions
constitutes the technique’s Achilles heel, we performed a limited comparison of COSMIC EDPs
with electron densities measured by sensors on the Communications/Navigation Outage Forecast
System (C/NOFS) satellite during conjunction intervals. Results show that COSMIC EDPs were
in closer agreement with ion densities measured by the C/NOFS than were those predicted by
widely used models. Third, we outline a new technique that combines the capabilities of sensors
on the COSMIC, C/NOFS and DMSP satellites to infer altitude profiles of electron and ion
temperatures (Te, Ti), mean ion masses <mi> and ionospheric scale heights H at altitudes between
the F-layer peak and 850 km. Data acquired during eight COSMIC-C/NOFS-DMSP conjunctions
on 24 – 25 October 2011 are used to demonstrate the proposed method’s feasibility then outline
our plan to apply it to large databases. Our ultimate goal is to specify topside EDP taxonomies
that occur at low latitudes as well as the temperature and mass distributions required to support
them.
Abstract
Outline and Objective
• This presentation addresses five questions:
(1) Where is GPS and how does it operate?
(2) What is COSMIC and what does it measure?
(3) How do COSMIC receptions of GPS signals get turned into EDPs?
(4) Can we trust COSMIC EDPs and learn something new from them?
(5) What value added do data from RPAs on C/NOFs and DMSP bring?
• Our objective is to introduce this audience to GPS-COSMIC capabilities
for providing useful information about the thermal structure and dynamics
of the low-latitude ionosphere in the altitude range 200 to 800 km.
Global Position System
• GPS consists of 24 operational satellites flying
in 55o inclined, circular orbits at an approximate
altitude of 22,000 km.
- 6 orbital planes with 4 satellites per plane
- Dual frequency transmitters
f1 = 1.57542 GHz
f2 = 1.2276 GHz
• GPS receivers identify incoming code with a
precision of better than 1 ns (30 cm) by receiver
clock from the carrier waves “precise ranging
code” (10.23 Mb/s).
• The accuracies of clocks between COSMIC and
GPS are 10 to 15 m and < 1μs.
Constellation Observing System for
Meteorology Ionosphere and Climate
• COSMIC is a joint Taiwan - US mission
that was launched into 72o inclined orbits
from Vandenberg AFB on 14 April 2006.
• It consists of 6 identical 3-axis stabilized
satellites
• Initial altitude: 500 km.
• Sequentially raised to ~ 800 km.
• Orbital nodes separated by ~ 2 hours
in local time.
COSMIC Payload
GOX Occultation Antenna
GOX Occultation Antenna
COSMIC-GPS Radio Occultations
Alt
itu
de
Temperature
EDP
Schematics of COSMIC-GPS
radio occultation events
Cosmic may rise above
or
sink below GPS horizon
Schreiner et al. (1999), Radio Sci.,
34, 949–966.
GPS-to-COSMIC Propagation:
• The well-known dispersion relation for EM waves propagating in the
ionosphere with >> pe >> ce >> en is: ,
where and
• The phase v and group vg speeds of the waves are:
• Group delays and phase advances depend only on electron
densities ne encountered along propagation path lengths s:
2 2 2 2( ) /pek c
2
22
2
2 2
2 2
(1 )2
1
1 (1 )2
pe
pe
pe pe
g
cv c
v c c
2
2 2 2
0
40.3
2 (2 )
COSMIC
e
e GPS
qt n ds STEC
c m f cf
2
0/ 2pe e e peq n m f 3( ) 8.98 ( )pe ef kHz n cm
Define the excess phase parameter S as the difference between signals
propagating in vacuum over distance |rCOSMIC – rGPS| and along S0 the
actual ray path through the ionosphere.
S = S0 - |rCOSMIC – rGPS|
where 1- fpe
2 / 2 f 2 is the index of refraction.
0
COSMIC
GPS
S ds
GPS-to-COSMIC Propagation: Applications
GPS-to-COSMIC Propagation: Applications
Schreiner et al. (1999) showed that
bending angles for L1 and L2 signals
are very small:
• 1.118 10-4 for ne = 1010 m-3
• 2.07 10-3 for ne = 1013 m-3
Hence, we assume that GPS signals
propagate along very similar paths.
Thus STEC can be calculated with
either f 1 or f 2 or both frequencies.
Bottom Line: Approximate GPS-COSMIC propagation paths as straight lines.
GPS-to-COSMIC Propagation: Applications
1 1 2 2 1 2 1 2
2 2
1 2
( )
40.3 40.3 40.3( )
S f S f S S f fSTEC
f f
• Using both frequencies any clock-based errors exactly cancel.
• Occultation intervals last about 12 minutes
• Since STEC measurements are recorded at rate of ~1 per second,
about 700 are accumulated to form each EDP.
• Inverse Abel transformations are then used to calculate ne along
vertical tangent lines.
0
0
0 0
2 2
0
( ) /1( )
COSMICr r
e
r r
dSTEC r drn r dr
r r
GPS-to-COSMIC Propagation: Applications
• r0 = distance from center of Earth to a specific altitude
• r = distance from center of Earth to height of tangent point
• ne profiles can then be integrated to obtain vertical TEC
Critical assumptions for valid Abel inversions:
(1) Propagation paths are nearly straight lines
(2) GPS and COSMIC orbits are nearly circular
(3) Electron density profiles are spherically symmetric,
i.e. horizontal gradients along ray paths are weak.
800
200
( )
km
e
km
VTEC n h dh
Cosmic Data Products and Availability
• COSMIC is administered by the
National Space Organization (NSPO)
and
the University Corporation for
Atmospheric Research (UCAR)
• EDP data are available in tabular
format via the internet from the
\Taiwan Analysis Center for COSMIC
(TACC): http://tacc.cwb.gov.tw/
and
UCAR: http://www.cosmic.ucar.edu/.
• The example to the right shows an EDP
and useful ephemeris information
derived from downloaded data files.
Complementary Data Sources: SSIES on DMSP & CINDI on C/NOFS
Current – Voltage Sweeps
e-
negative bias
swept voltage
negative bias
collector plate
i+ i+
to electronics
photo & secondary
electrons
Vsat
RPA Schematic RPA Measurements:
(1) 3 components of ion drift
velocities (Vi)
(2) Ni tot, Ni O+, and Ni light
(3) Ion temperatures Ti
(4) Mean ion mass < mi >
• SSIES has a boom-mounted
spherical Langmuir probe to
measure electron densities Ne
and temperatures Te.
• Infer topside scale heights
H = kB(Te +Ti) / < mi> g
Log I
-6 -4 -2 0 2 4 6 8 10
Slope -1/Ti
Intercept Ni
Applied Voltage
Two COSMIC Case Studies: Solar Min and Max Storms
• To help understand COSMIC measurements we undertook two case studies
• The first case focused on VTEC measurements acquired during an 80-day period
in late 2007 in which ejecta from a coronal hole swept by Earth three times.
• During the first and third encounters the corotating interaction region (CIR)
at the leading edge of the high-speed stream evoked weak responses in
the dayside ionosphere.
• Strong responses seen during the second encounter demonstrated effects of
penetrating electric fields generated by complex interplanetary sources that
included the near simultaneous arrival of an ICME.
• The second case study sought to determine whether COSMIC EDPs are
trustworthy. Their differences from predictions of the NeQuick model led
previous investigators to conclude that horizontal electron density gradients
degrade COSMIC EDPs to unacceptable levels. We present empirical
tests of this dire conclusion.
Case Study 1: November 2007 Storm
EIT image from SOHO on
18 November 2007 showing
a large coronal hole near the
Sun’s central meridian
Schematic representation of a corotating
region at the leading edge of a high speed
stream in the solar wind approaching Earth.
Within streams nSW is very low.
Magnetic flux emanating from coronal holes are unipolar, with radial
components that point either toward or away from the Sun.
Case Study 1: November 2007 Storm
80-day period centered on
the November 2007 storm:
(A) F10.7: daily and 81-day running
averages
(B) NSW (red) and VSW (blue)
(C) IMF BX (blue) and BY (red)
(D) Magnetospheric electric field
(E) Dst index
Vertical dash, marking the arrivals of high speed streams in the vicinity
Earth, are separated by 27-day solar rotation periods.
Case Study 1: November 2007 Storm
Days 322 – 327, 2007
(A) Solar wind density (red) and speed
(blue)
(B) IMF BX (blue) and BY (red):
Note: crossing of heliospheric current
sheet (HCS).
(C) IMF BY (red) and BZ (blue)
(D) Magnetospheric E field (~ 1 mV/m)
(E) Sym-H index minimum (~ -70 nT)
Note: relative UTs of ICME, CIR,
HSS and HCS
UT
• VTEC Distribution sampled by
COSMIC plotted as functions
of local time in 9 latitude bins
in northern (left) and southern
(right) hemispheres.
• From this perspective VTEC
increased during the storm’s
main phase and soon relaxed.
• Apparently, no surprises!
Case Study 1: November 2007 Storm
COSMIC VTEC versus Local Time
Case Study 1: November 2007 Storm COSMIC VTEC versus Universal Time
• Distribution of VTEC sampled by
COSMIC: days 322 – 327, 2007
plotted as functions of universal time
in 9 latitude bins in northern (left)
and southern (right) hemispheres.
• Sym-H index and VS in bottom plots
• Viewed from this perspective we
see that VTEC increased on during
day of the storm’s main phase then
relaxed.
• Decreased during first half of say 325!
• Why? Penetration electric field
and deviation from photo-
chemical equilibrium.
① ②
④ ⑥
COSMIC EDPs: Study 2 COSMIC – C/NOFS – DMSP
Conjunctions
CV
24 and 25 October 2011
Interplanetary Drivers and
Geomagnetic Responses
0
10
20
30
40
0
200
400
600
800
NS
W (
cm-3
)
PS
W (
nP
a)
VS
W (k
m/s)
-30
-20
-10
0
10
20
30
BX
BY
BZ
(n
T)
-200
-150
-100
-50
0
50
100
297:00 297:12 298:00 298:12 299:00
Sy
m H
(n
T)
Main
Phase
Recovery
Phase SSC
Top Panel Traces:
• NSW density (red)
• VSW speed (black)
• PSW dynamic pressure (blue)
Middle Panel Traces
• IMF BX (black)
• IMF BY (red) 1-minute averages
• GSM coordinates • IMF BZ (blue)
Bottom Panel Trace:
• Sym H index (black)
• Red dots indicate UT of EDP acquisitions.
• Vertical dashed lines mark beginnings
of main & recovery phases
COSMIC EDP: Study 2 Interplanetary and Storm Dynamics
COSMIC EDP: Study 2 C/NOFS and Model Comparisons
Z
Pre
-Sto
rm
Main
Ph
ase
Reco
ver
y
Midnight Dawn Noon Dusk (A-P)
(A-M)
(A-R)
(B-M)
(B-P)
(B-R)
(C-P)
(C-M)
(C-R) (D-R)
(D-P)
(D-M)
COSMIC EDP Study Statistical Comparisons with C/NOFS
1000
104
105
106
107
1000 104
105
106
107
PB
Mod
:
Ne [
cm-3
]
C/NOFS: Ni [cm
-3]
Ne = 6.31 * N
i 0.848
R = 0.774
1000
104
105
106
107
1000 104
105
106
107
NeQ
uic
k:
N
e [cm
-3]
C/NOFS: Ni [cm
-3]
Ne = 37.88 * N
i 0.698
R = 0.799
1000
104
105
106
107
1000 104
105
106
107
CO
SM
IC:
N
e [
cm-3
]
C/NOFS: Ni [cm
-3]
Ne = 0.612 * N
i 1.03
R = 0.858
Electron densities from EDPs:
• COSMIC (left) Log – Log Plots
• NeQuick (middle) Power - Law Regression Analyses
• PBMod (right)
Plotted as functions of Ni measured at C/NOF altitudes on days 297 ( ) and 298 ( ).
Dotted lines are guides indicating results if inferred Ne from EDPs = Ni from CNOFS
650 700 750 800 850 900 950
Altitude (km)
650 700 750 800 850 900 950
10
11
12
13
14
Altitude (km)
Ln
Ne (
cm-3
)
( ) ( )1/
( )
e B e i
i
dLn N k T TH
dh m g h
Top:
• Orange, black and purple
lines mark EDPs from
PBMod, COSMIC & NeQuick
• Red/blue dots show Ni
from C/NOFS / DMSP
Bottom:
• Linear regressions Ln (Ne)
versus altitude for h > 700 km
COSMIC Electron Density Profiles
Topside Scale Heights
COSMIC-CNOFS-DMSP Conjunctions
Event Te (K) Ti (K) HDMSP (km) HCOS (km) HNeQ (km) HPBM (km)
1 1697 1801 236.7 233.5 231.4 236.0
2 2997 2512 372.6 346.7
204.4 351.5
COSMIC Electron Density Profiles
Topside Scale Heights
At DMSP altitudes RPA data showed that O+ was the dominant ion
High degree of agreement achieved between scale heights calculated with mi, Te, Ti
from DMSP and those from COSMIC and PBMod EDP slopes.
Recently we developed a low-pass, Fourier fitting procedure that
is piecewise continuous at the altitude of the F layer peak h = hp
12
12.5
13
13.5
14
14.5
15
12 12.5 13 13.5 14 14.5 15L
n (
Ne*)
Ln (Ne COSMIC
)
Ln (Ne*) = 0.00016 + 0.9999 Ln (N
e COSMIC )
R = 1
12
12.5
13
13.5
14
14.5
15
200 300 400 500 600 700 800 900
Ln
(N
e C
OS
MIC
)
Ln
(N
e*)
h (km)
UT: 297:10:00
GLat: 6.8o
GLong: 104o
LT: 17:00
Ne max
: 1.47 106 cm
-3
hp 433 km
4
*
0
ln ( ) ( ) ( )e p k k
k
N h h a Cos k b Sin k
| |
800
p
p
h h
h
4
*
0
ln ( ) ( ) ( )e p k k
k
N h h c Cos k d Sin k
| |
200
p
p
h h
h
1*( ) ( )
( )
B e i e
i
k T T dLn NH
m g h dh
( ) ( ) ( )( ) ( )i
e i
B
m h g h H hT h T h
k
COSMIC Electron Density Profiles
Fitting Procedure
Case 1
In all examples R > 0.999
CINDI on CNOFS measures: <mi>, Ti and Vi
Since
COSMIC & PBMod EDPs
with 1st and 2nd Derivatives
during conjunctions with CNOFS & DMSP
10
11
12
13
14
15
200 300 400 500 600 700 800 900
CASE 1
Ln Ne PBMLn(Ne cosmic)Ln Ni CNOFSLn Ni DMSP
Ln
Ne L
n N
i C
osm
ic
PB
M
CN
OF
S
DM
SP
h (km)
UT: 297:10:00
GLat: 6.8o
GLong: 104o
LT: 17:00
Ne max
: 1.47 106 cm
-3
hp 433 km
-0.01
-0.005
0
0.005
0.01
200 300 400 500 600 700 800 900
d L
n N
e /
dh
(k
m-1
): C
OS
MIC
PB
M
h (km)
-0.005
0
0.005
200 300 400 500 600 700 800 900
d2 L
n N
e/d
h2 (
km
-2):
C
OS
MIC
P
BM
h (km)
10
11
12
13
14
15
200 300 400 500 600 700 800 900
Ln (Ne*)Ln Ne PBMLn (Ne CNOFS)
Ln (Ne DMSP)Ln
Ne:
C
OS
MIC
P
BM
C
NO
FS
D
MS
P
h (km)
Case 2 UT: 297:04:39
LT: 08:00
GLat: 4.8o
GLong: 50.2o
Ne max: 1.49 106 cm
-3
hp: 279 km
-0.01
-0.005
0
0.005
0.01
200 300 400 500 600 700 800 900
d L
n N
e /d
h (
km
-1):
C
OS
MIC
P
BM
h (km)
-0.002
-0.001
0
0.001
0.002
200 300 400 500 600 700 800 900
d2 L
n N
e /
dh
2 (
km
-2)
CO
SM
IC
PB
M
h (km)
COSMIC & PBMod EDPs
with 1st and 2nd Derivatives
during conjunctions with CNOFS & DMSP
-0.01
0
0.01
100 200 300 400 500 600 700 800 900
d2 L
n N
e / d
h2 (
km
-2):
C
OS
MIC
P
BM
h (km)
-0.02
-0.01
0
0.01
0.02
200 300 400 500 600 700 800 900
d L
n N
e / d
h (
km
-1):
C
OS
MIC
P
BM
h (km)
10
11
12
13
14
15
200 300 400 500 600 700 800 900
CASE 3
Ln (Ne*)
Ln Ne PBMLn (Ne CNOFS)Ln (Ne DMSP)
Ln
Ne:
CO
SM
IC P
BM
C
NO
FS
D
MS
P
h (km)
UT: 297:19:00
LT: 08:00
GLat: -5.8o
GLomg: 154o
Ne max
: 3.77 10U cm-3
hp: 300 km
-0.02
-0.01
0
0.01
0.02
200 300 400 500 600 700 800 900
d L
n N
e /d
h (
km
-1):
C
OS
MIC
P
BM
h (km)
-0.02
-0.01
0
0.01
0.02
200 300 400 500 600 700 800 900
d L
n N
e /d
h (
km
-1):
C
OS
MIC
P
BM
h (km)
9
10
11
12
13
14
200 300 400 500 600 700 800 900
Ln (Ne*)
Ln Ne PBMLn (Ne CNOFS)Ln (Ne DMSP)
Ln
Ne:
C
OS
MIC
P
BM
C
NO
FS
D
MS
P
h (km)
Case 4 UT: 297:19:15
LT: 04:55
GLat: -4.8o
GLong: 145o
Ne max
: 2.7 105 cm
-3
hp: 270 km
COSMIC & PBMod EDPs
with 1st and 2nd Derivatives
during conjunctions with CNOFS & DMSP
-0.01
-0.005
0
0.005
0.01
200 300 400 500 600 700 800 900
d2 L
n N
e / d
h2 (
km
-2):
C
OS
MIC
P
BM
h (km)
-0.01
-0.005
0
0.005
0.01
200 300 400 500 600 700 800 900
d L
n N
e /d
h (
km
-1):
C
OS
MIC
P
BM
h (km)
10
11
12
13
14
15
200 300 400 500 600 700 800 900
CASE 5
Ln (Ne*)Ln Ne PBMLn (Ne CNOFS)Ln (Ne DMSP)
Ln
Ne:
C
OS
MIC
P
BM
C
NO
FS
D
MS
P
h (km)
UT: 297:04:39
LT: 18:37
GLat: 7.1o
GLong: 59.4o
Ne max
: 1.42 106 cm
-3
hp: 342 km
-0.005
0
0.005
200 300 400 500 600 700 800 900
d2
Ln
Ne /
dh
2 (
km
-2):
C
OS
MIC
P
BM
h (km)
-0.02
-0.01
0
0.01
0.02
200 300 400 500 600 700 800 900
d L
n N
e/dh
(k
m-1
) C
OS
MIC
P
BM
h (km)
10
11
12
13
14
15
200 300 400 500 600 700 800 900
CASE 6 Ln (Ne*)Ln Ne PBMLn (Ne CNOFS)
Ln (Ne DMSP)
Ln
Ne:
C
OS
MIC
P
BM
C
NO
FS
D
MS
P
h (km)
UT: 298:12:55
LT: 18:00
GLat 4.5o
GLong: 76o
Ne max
: 1.66 106 cm
-3
hp: 472 km
COSMIC & PBMod EDPs
with 1st and 2nd Derivatives
during conjunctions with CNOFS & DMSP
-0.001
0
0.001
200 300 400 500 600 700 800 900
d2 L
n N
e /
dh
2 (
km
-2):
C
OS
MIC
P
BM
h (km)
-0.02
-0.01
0
0.01
0.02
200 300 400 500 600 700 800 900
d L
n N
e /
dh
C
OS
MIC
P
BM
h (km)
10
11
12
13
14
15
200 300 400 500 600 700 800 900
Case 8
Ln (Ne*)Ln Ne PBMLn (Ne CNOFS)
Ln (Ne DMSP)
Ln
Ne:
C
OS
MIC
P
BM
C
NO
FS
D
MS
P
h (km)
UT: 297:03:39
LT: 05:45
GLat: -9.5o
GLong: 34.1o
Ne max
: 7.3 105 cm
-3
hp: 238 km
10
11
12
13
14
15
200 300 400 500 600 700 800 900
CASE 7
Ln (Ne*)Ln Ne PBMLn (Ne CNOFS)Ln (Ne DMSP)
Ln
Ne:
C
OS
MIC
P
BM
C
NO
FS
D
MS
P
h (km)
UT: 298:03:15
LT: 05:12
GLat: -6.3o
GLong: 26.7o
Ne max
: 4.4 105 cm
-3
hp: 277 km
-0.005
0
0.005
200 300 400 500 600 700 800 900
d2 L
n N
e / d
h2 (k
m-2
): C
OS
MIC
P
BM
h (km)
-0.01
-0.005
0
0.005
0.01
200 300 400 500 600 700 800 900
d L
n N
e / d
h (k
m-1
): C
OS
MIC
P
BM
h (km)
COSMIC Electron Density Profiles
Summary and Conclusions:
• Presented case studies were undertaken to establish a feasible methodology
for testing the reliability of COSMIC-based topside EDPs and VTEC estimates
• The November 2007 and October 2011 storms provided a variety of external
driving conditions.
• The PLP on CNOFS provided high resolution ion densities for comparison with
EDPs estimated from COSMIC STEC measurements and model predictions.
• EDPs from COSMIC acquired within 15 were in better agreement with CNOFS
Ni measurements than model predictions.
• Early comparisons indicate that further study and analysis is worthwhile, using
Ni , Ti and Te from DMSP and C/NOFS to estimate topside thermal distributions.
• We have taken first steps towards developing an AI approach to EDP evaluations.