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Gravity Wave Characteris/cs from OH airglow imager at Andes Lidar Observatory, Chile(30S,71W) and
Comparison with Maui
Zhenhua Li1, Alan Liu2, Gary Swenson1 1 University of Illinois at Urbana‐
Champaign 2Embry‐Riddle Aeronau/cal University
Outline
• Observa/on site and data • Brief introduc/on on method
• Wave characteris/cs and comparison with Maui, Hawaii
ALO (30S, 70W)
Total number of observa/on
ALO
1 2 3 4 5 6 7 8 9 10 11 120
5
10
15
20
25Nights with more than 20 minutes good observation
Month
2009−09 to 2010−09
Maui
1 2 3 4 5 6 7 8 9 10 11 120
10
20
30
40
50
60
70Nights with more than 20 minutes good observation
Month
200220032004200520062007
Method
• Gravity wave spectra (horizontal wavelength and propaga/on direc/o)are iden/fied through 2‐D FFT on /me‐difference OH airglow images
• Phase speed and wave period are inferred from phase progression between consecu/ve images
Horizontal Wavelength
ALO
10 20 30 40 50 60 70 80 90 100 110 120 130 140 1500
100
200
300
400
500
600
Horizontal wavelength (km)
Num
ber o
f wav
e ev
ents
Maui
10 20 30 40 50 60 70 80 90 100 110 120 130 140 1500
500
1000
1500
2000
2500
3000
3500
Horizontal wavelength (km)
Num
ber o
f wav
e ev
ents
Intrinsic phase speed
ALO
20 40 60 80 100 120 140 160 1800
100
200
300
400
500
600
Histogram of intrinsic phase speed (m/s)
Maui
20 40 60 80 100 120 140 160 1800
200
400
600
800
1000
1200
1400
1600
1800
Histogram of intrinsic phase speed (m/s)
Observed phase speed
ALO
0 50 100 1500
50
100
150
200
250
300
350
400
450
Histogram of observed phase speed (m/s)
Maui
0 50 100 1500
500
1000
1500
Histogram of observed phase speed (m/s)
Intrinsic wave period
ALO
0 10 20 30 40 50 600
50
100
150
200
250
300
350
400
Wave period (minutes)
Num
ber o
f wav
e ev
ents
Maui
0 10 20 30 40 50 600
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
Wave period (minutes)
Num
ber o
f wav
e ev
ents
Observed wave period
ALO
0 10 20 30 40 50 600
50
100
150
200
250
300
350
Observed Wave period (minutes)
Num
ber o
f wav
e ev
ents
Maui
0 10 20 30 40 50 600
200
400
600
800
1000
1200
1400
1600
1800
2000
Observed Wave period (minutes)
Num
ber o
f wav
e ev
ents
Ver/cal wavelength
ALO
10 20 30 40 50 60 70 800
100
200
300
400
500
600
700
800
Vertical wavelength (km)
Num
ber o
f wav
e ev
ents
Maui
10 20 30 40 50 60 70 800
200
400
600
800
1000
1200
Vertical wavelength (km)
Num
ber o
f wav
e ev
ents
Wave occurrence frequency
ALO
Month
UT
2 4 6 8 10 12−1
0
1
2
3
4
5
6
7
8
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Maui
Month
UT
2 4 6 8 10 126
7
8
9
10
11
12
13
14
15
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Gravity wave transmission through lower atmosphere
ALO
Month
UT
Percentage of waves that transmitted above 80 km
2 4 6 8 10 121
2
3
4
5
6
7
8
9
10
0.4
0.45
0.5
0.55
0.6
0.65
Maui
Month
UT
Percentage of waves that transmitted above 80 km
2 4 6 8 10 126
7
8
9
10
11
12
13
14
15
0.3
0.35
0.4
0.45
0.5
0.55
0.6
Wave propaga/on direc/on, ALO 50JAN 50FEB 50MAR
30APR 15MAY 12JUN
30JUL 40AUG 25SEP
8OCT 40NOV 15DEC
Summer: dominantly toward summer Pole
Generally a preference toward SW thoughout the year.
Maui, wave propaga/on direc/on
150N
S
W E
JAN 80N
S
W E
FEB 250N
S
W E
MAR
300N
S
W E
APR 250N
S
W E
MAY
150N
S
W E
JUN
150N
S
W E
JUL 250N
S
W E
AUG 250N
S
W E
SEP
150N
S
W E
OCT
150N
S
W E
NOV
150N
S
W E
DEC
During winter/summer, preferen/ally propaga/on toward summer pole.
Wave propaga/on direc/on rela/ve to local mean wind
ALO
2%
4%
6%
8%
180 0
−90
90
0 − 20
20 − 40
40 − 60
60 − 80
80 − 100
100 − 120
120 − 140
140 − 160
Direction Difference
Observed Phase Speed (m/s)
Maui
2%
4%
6%
8%
180 0
−90
90
0 − 20
20 − 40
40 − 60
60 − 80
80 − 100
100 − 120
120 − 140
140 − 160
Direction Difference
Observed Phase Speed (m/s)
Doppler‐shi\ effects
2
4
6
8
30
210
60
240
90
270
120
300
150
330
180 0
Vertical Wavelength and Cancellation Factorvs Direction Difference with Mean Wind (T=10 minute,Lx=25 km)
Vertical Wavelength (10 km)Cancellation Factor
Summary
• Gravity waves observed over ALO, Chile have longer horizontal wavelength, longer wave period than those over Maui
• Waves at both sites tend to propagate against local mean wind demonstra/ng the effects of Doppler‐shi\ing
• The difference in wave parameters in the two sites implies dominant wave sources for the two sites are different. Especially, for ALO, there seem to be a dominant source region in the NE direc/on.
• Wave occurrence frequencies at both sites match well with wave transmission through the mean flow.
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