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.