1/162005 CEDAR-GEM Joint Workshop , Santa Fe, New Mexico, June 26 - July 1, 2005

Fechine, J.1, Medeiros, A. F.2, Buriti, R. A.2 Takahashi, H.1, Wrasse, C.M.1

Contact: joaquim@laser.inpe.br

1 - Instituto Nacional de Pesquisas Espaciais (INPE), Brazil2 - Universidade Federal de Campina Grande, Brazil

Optical Observation of Mesospheric Bores in the Equatorial MLT Region

AbstractMesospheric bore events were observed and analyzed in the equatorial region. An all-sky CCD imager designed to measure wave structure of the OH, O2b(0,1) and OI557.7 nm airglow emission layers has been operated near the equatorial region at São João do Cariri (Cariri), Brazil, (7.4 S, 36.5 W). A large number of gravity wave was observed from September 2000 to September 2002 and among them 64 wave events were identified as mesospheric bores. The bore front shows a horizontal extension larger than 1000 km, showing a complementary brilliance between the three emissions. Their predominant characteristics as well as the occurrence, local time dependency, morphology and propagation direction will be presented and discussed.

2/162005 CEDAR-GEM Joint Workshop , Santa Fe, New Mexico, June 26 - July 1, 2005

1.INTRODUCTION

Pororoca in Guamá river, Brasil. Morning’s glory in Australia.

Tropospheric boreRiver bore Mesospheric bore

O2 airglow, S. J. Cariri, Brazil.

Bore is a front wave phenomena generally observed in rivers and in the troposphere, but only recently it was observed in the mesosphere.

Dewan and Picard (1998, 2000) proposed a Mesospheric bore´s model to explain the airglow observations of Taylor et al., (1995).This model was made from channel bore approach from the mass and momentum conservation.

Generation mechanism of channel bore

3/162005 CEDAR-GEM Joint Workshop , Santa Fe, New Mexico, June 26 - July 1, 2005

1.1 Passage of Bore in the Mesospheric Duct

S. J. Cariri, Brazul - 28/12/2000

WarmerDenserBrighter

Layer OH (87 km)

Layer O2 (94 km)

ColderRarefyDarker

z

S

B o re

P la ne o f S y m m etry

O2

OH

Dewan and Picard (1998, 2000) model showing the duct between OH and O2 airglows layers that would support the internal mesospheric bore with its symmetric displacements upward and downward about the plane of symmetry. The upper layer (O2) would became rarefy, colder and darker, while the bottom layer (OH) would became denser, warmer and brighter.

4/162005 CEDAR-GEM Joint Workshop , Santa Fe, New Mexico, June 26 - July 1, 2005

1.2 Identification of Mesospheric Bore

How did we identify the bore event ?

1. Presence of extended wave front, bright in one airglow layer and dark in the other layer.

2. Wave front following to some wave crests,

3. Simultaneous occurrence of wave front in different airglow layers,

4. Ducting condition (ex. temperature inversion)

S. J. Cariri, Brazul - 28/12/2000

O2

5/162005 CEDAR-GEM Joint Workshop , Santa Fe, New Mexico, June 26 - July 1, 2005

Bore 9 - OH 20001225 Bore 10 - O5 20001228 Bore 16 - O5 20010123

Bore 29 - OH 20010624Bore 18 - O5 20010223 Bore 49 - O5 20020417

1.3 Mesospheric Bores at Cariri

Sep 2000 to sep 2002 226 nights - 1768 h

O5 O5

O5 O5

OH

OH

6/162005 CEDAR-GEM Joint Workshop , Santa Fe, New Mexico, June 26 - July 1, 2005

2.1 Results: Bore Frequency of Occurrence

From Sep/2000 to Sep/2002 - S. J. Cariri (7,4 S 36,5 W)

0

200

400

600

800

Gravity waves Bores

No o

f E

ven

ts

~ 660 events

64 events

~ 10%

GW Total Events

Bore total events

The occurrence of bore events was about 10% relative to all gravity waves events observed at Cariri, showing that this kind of event can not be considered rare in the equatorial region.

7/162005 CEDAR-GEM Joint Workshop , Santa Fe, New Mexico, June 26 - July 1, 2005

2.2 Incidence of Bores in S. J. do Cariri

No seasonal trend was observed in the bore occurrence, in contrast to gravity wave band type behavior.

0,00

0,01

0,02

0,03

0,04

0,05

0,06

0,07

0,08

0,09

Set Out Nov Dez Jan Fev Mar Abr Mai Jun Jul Ago Set Out Nov Dez Jan Fev Mar Abr Mai Jun Jul Ago Set

No de pororocas/hsde observação

Incidência de Pororocas/hora

Set/2000 a Set/2002 - S. J. Cariri (7,4oS 36,5oO)

200220012000

7 eventos 11 eventos 9 eventos 9 eventos 5 eventos 3 eventos 9 eventos 9 eventos3 ev.

No of Bores/ h of observation Sep/2000 to Sep/2002 – S. J. Cariri (7,4S 36,5W)

7 events 11 events 9 events 9 events 9 events 9 events5 events 3 events

8/162005 CEDAR-GEM Joint Workshop , Santa Fe, New Mexico, June 26 - July 1, 2005

2.3 Bore Characteristics

69%

9% 20%

2%

Propagation Direction Distribution Development of Bores

Preferential direction to NE and E, the same direction of bands.

Large number of bores was observed with well developed front and train.

The major part was observed between 20 - 22 hs (LT).

59% Hour of Occurrence

0

2

4

6

8

10

12

14

16

18

20

22

24

18 – 20 hs 20 – 22 hs 22 – 24 hs 24 – 02 hs 02 – 04 hs 04 – 06 hs

No o

f B

ore

s

(local time)

9/162005 CEDAR-GEM Joint Workshop , Santa Fe, New Mexico, June 26 - July 1, 2005

2.4 Characteristics of the Wave Train

0 10 20 30 40 50 60 70 80 90 1000123456789

101112

No o

f B

ore

s

Horizontal phase velocity (ms-1)

WavelengthTotal: 48 cases

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 8002468

1012141618202224

No o

f B

ore

s

Horizontal Wavelength (km)

No of crestTotal: 45 cases

PeriodTotal: 45 cases Phase velocity

Total: 34 cases

10/162005 CEDAR-GEM Joint Workshop , Santa Fe, New Mexico, June 26 - July 1, 2005

2.5 Presence of Gravity Wave Activity(before, during and after the bore event)

73%

3%

75%

25%

63%

33%

4%

24% before

after

during

For modeling the mesospheric

bore, it is very important that high

gravity wave activity is observed

before, during and after a bore

event. This effect is important for

the generation mechanism.

11/162005 CEDAR-GEM Joint Workshop , Santa Fe, New Mexico, June 26 - July 1, 2005

3. DISCUSSIONAIRGLOW RESPONSE TO THE BORE

PROPAGATION

OH (bright)

O (bright)2

OI 5577 (dark)

BBD Bore 17 - 20010223

Duct

OH (bright)

O (bright)2

OI 5577 (dark)

Bore 17 - 20010223

Duct

OH (bright)

O (bright)2

OI 5577 (bright)

BBB Bore 40 - 20011022

Duct

OH (bright)

O (bright)2

OI 5577 (bright)

Bore 40 - 20011022

Duct

OH (bright)

O (dark)2

OI 5577 (dark)

BDD Bore 18 - 20010223

Duct

OH (bright)

O (dark)2

OI 5577 (dark)

Bore 18 - 20010223

DuctOH (dark)

O (dark)2

OI 5577 (dark)

DDD Bore 14 - 20010122

Duct

OH (dark)

O (dark)2

OI 5577 (dark)

Bore 14 - 20010122

Duct

Some complementarity effects (bright and dark) in the emission intensity of the airglow layers were predicted by Dewan and Picard (1998) model.

12/162005 CEDAR-GEM Joint Workshop , Santa Fe, New Mexico, June 26 - July 1, 2005

3.1 Complementary Effects Observed

9% 8%

28%

23% 20%

11% Not Predicted

02468

101214161820

B B B B B D B D D D D D D B B D D B others

No o

f B

ores

OH (dark)

O (dark)2

OI 5577 (bright)

DDB Bore 37 - 20010921

Duct

OH (dark)

O (bright)2

OI 5577 (bright)

DBB Bore 02 - 20000928

Duct

Complementarity effect not predicted Complementarity effect not predicted

Some observed complementarity effects was not predicted by the model.

13/162005 CEDAR-GEM Joint Workshop , Santa Fe, New Mexico, June 26 - July 1, 2005

3.2 Relationship between ΔInt. and ΔTemp.

Behavior predictedTaylor et al., 1995

20:00 20:15 20:30 20:45 21:00 21:15 21:30 21:45 22:00

H O R A LO C A L (hr)

2000

2200

2400

2600

INT

EN

SID

AD

E (

R)

INTENSIDADE DO OH

20:00 20:15 20:30 20:45 21:00 21:15 21:30 21:45 22:00

H O R A LO CAL (hr)

210

215

220

225

230

235

TE

MP

ER

AT

UR

A (

K)

TEMPERATURA ROTACIONAL DO OH

INTENSITY OH

LOCAL TIME (h)

ROTATIONAL TEMPERATURE OH

LOCAL TIME (h)

TE

MP

ER

AT

UR

E (

K)

INT

EN

SIT

Y (

R) Int. OH

T OH

Int. OH

T OH

Some bore at Cariri showed a decrease of the OH rotational temperature simultaneous to an increase of the OH airglow emission. This behavior was not expected from model predictions was not yet reported in literature.

Behavior not predictedBore at Cariri

149,4 R/min

13,1%

-7,2 K/min

-5,7%

14/162005 CEDAR-GEM Joint Workshop , Santa Fe, New Mexico, June 26 - July 1, 2005

3.3 Temperature Variations

0%

10%

20%

30%

40%

50%

TOH TO2 TOH TO2 TOH TO2 TOH TO2

Temperature VariationsSep/2000 to Sep/2002 - S. J. Cariri (7,4oS 36,5oW)

The response of the airglow temperature was different under the bore propagation. Some events showed an increase (or decrease) in the temperature at two airglows layers, TOH and TO2 simultaneously. Other events showed an inverse behavior of the temperature, between two airglow layers, suggesting a possible influence of the chemical reactions in the response of the airglow temperature.

15/162005 CEDAR-GEM Joint Workshop , Santa Fe, New Mexico, June 26 - July 1, 2005

3.4 Analysis of m2 of the Bores EventsThe propagation condition, m2 was calculated using wind model.

The results suggest that we have both propagating and evanescent waves.

16/162005 CEDAR-GEM Joint Workshop , Santa Fe, New Mexico, June 26 - July 1, 2005

4. Conclusions 1. The mesospheric bore events were observed with a frequency

of occurrence with 10% of the total gravity wave events

2. The bore characteristics agree with Dewan and Picard (1998) model, but with some exceptions;

3. No seasonal trend was observed in the equatorial region;

4. At the first time it was observed:• non-undulate bores• bores in formation and/or dissipation• nights with more than one bore event;

5. It was verified a high activity of gravity wave before the bores, corroborating in the generation mechanism, interaction of gravity wave – critical level, as suggested by Dewan and Picard.