1. 2005 CEDAR-GEM Joint Workshop, Santa Fe, New Mexico, June 26 - July 1, 2005 1/16 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), Brazil 2 - Universidade Federal de Campina Grande, Brazil Optical Observation of Mesospheric Bores in the Equatorial MLT Region Abstract Mesospheric bore events were observed and analyzed in the equatorial region. An all-sky CCD imager designed to measure wave structure of the OH, O 2 b(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. 2005 CEDAR-GEM Joint Workshop, Santa Fe, New Mexico, June 26 - July 1, 2005 2/16 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. 2005 CEDAR-GEM Joint Workshop, Santa Fe, New Mexico, June 26 - July 1, 2005 3/16 1.1 Passage of Bore in the Mesospheric Duct S. J. Cariri, Brazul - 28/12/2000 Warmer Denser Brighter Layer OH (87 km) Layer O 2 (94 km) Colder Rarefy Darker O2 OH Dewan and Picard (1998, 2000) model showing the duct between OH and O 2 airglows layers that would support the internal mesospheric bore with its symmetric displacements upward and downward about the plane of symmetry. The upper layer (O 2 ) would became rarefy, colder and darker, while the bottom layer (OH) would became denser, warmer and brighter.

4. 2005 CEDAR-GEM Joint Workshop, Santa Fe, New Mexico, June 26 - July 1, 2005 4/16 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. 2005 CEDAR-GEM Joint Workshop, Santa Fe, New Mexico, June 26 - July 1, 2005 5/16 Bore 9 - OH 20001225Bore 10 - O5 20001228Bore 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 OH

6. 2005 CEDAR-GEM Joint Workshop, Santa Fe, New Mexico, June 26 - July 1, 2005 6/16 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 wavesBores N o of Events ~ 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. 2005 CEDAR-GEM Joint Workshop, Santa Fe, New Mexico, June 26 - July 1, 2005 7/16 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. N o of Bores/ h of observation Sep/2000 to Sep/2002 – S. J. Cariri (7,4S 36,5W) 7 events 11 events 9 events 5 events3 events

8. 2005 CEDAR-GEM Joint Workshop, Santa Fe, New Mexico, June 26 - July 1, 2005 8/16 2.3 Bore Characteristics 69% 9% 20% 2% Propagation Direction DistributionDevelopment 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 hs20 – 22 hs22 – 24 hs24 – 02 hs02 – 04 hs04 – 06 hs N o of Bores (local time)

9. 2005 CEDAR-GEM Joint Workshop, Santa Fe, New Mexico, June 26 - July 1, 2005 9/16 2.4 Characteristics of the Wave Train Wavelength Total: 48 cases N o of crest Total: 45 cases Period Total: 45 cases Phase velocity Total: 34 cases

10. 2005 CEDAR-GEM Joint Workshop, Santa Fe, New Mexico, June 26 - July 1, 2005 10/16 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. 2005 CEDAR-GEM Joint Workshop, Santa Fe, New Mexico, June 26 - July 1, 2005 11/16 3. DISCUSSION AIRGLOW 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 Bore40-20011022 Duct OH (bright) O (bright) 2 OI 5577 (bright) Bore40-20011022 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 Duct OH (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. 2005 CEDAR-GEM Joint Workshop, Santa Fe, New Mexico, June 26 - July 1, 2005 12/16 3.1 Complementary Effects Observed 9% 8% 28% 23% 20% 11% Not Predicted 0 2 4 6 8 10 12 14 16 18 20 B B BB B DB D DD D DD B BD D Bothers N o of Bores 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 Some observed complementarity effects was not predicted by the model.

13. 2005 CEDAR-GEM Joint Workshop, Santa Fe, New Mexico, June 26 - July 1, 2005 13/16 3.2 Relationship between ΔInt. and ΔTemp. Behavior predicted Taylor et al., 1995 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 predicted Bore at Cariri 149,4 R/min 13,1% -7,2 K/min -5,7%

14. 2005 CEDAR-GEM Joint Workshop, Santa Fe, New Mexico, June 26 - July 1, 2005 14/16 3.3 Temperature Variations 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. 2005 CEDAR-GEM Joint Workshop, Santa Fe, New Mexico, June 26 - July 1, 2005 15/16 3.4 Analysis of m 2 of the Bores Events The propagation condition, m 2 was calculated using wind model. The results suggest that we have both propagating and evanescent waves.

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