S OUTLINE S Introduction S Nonlinear interaction between tides and - - PowerPoint PPT Presentation

S

Nonlinear interaction between an ultrafast Kelvin wave and the diurnal tide and their effects on the MLT airglow Fabio Egito1, Ricardo Buriti2, Amauri Medeiros2, Hisao Takahashi3

1-Federal University of Reconcavo Bahia-UFRB 2-Federal University of Campina Grande, UFCG 3- National Institute for Space Research-INPE

OUTLINE

S Introduction

S Nonlinear interaction between tides and planetary waves S Kelvin waves

S Instruments and data S Results

S The 3-4 day ultrafast Kelvin wave (UFKW) in the wind and

airglow

S The nonlinear interaction between the UFKW and diurnal

tide S Conclusions S Acknowledgements

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Introduction

S Kelvin waves

S Equatorially trapped waves that propagate eastward and present

• nly perturbation in the zonal direction;

S Generated in the troposphere by convective activity; S Partially forcing of the well known Intraseasonal (ISO),

Semiannual (SAO) and Quasi-biennial (QBO) oscillations (Andrews, 1987; Miyoshi and Fujiwara, 2006) by transporting eastward momentum;

S Day-to-day variability of the equatorial ionosphere (e.g.

Takahashi et al., 2007; Onohara et al., 2011, England et al., 2012);

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Period (days) Horizontal phase speed Vertical wavelength Slow Kelvin waves (SK) 15-20 20-40 m/s ~ 10 km Fast Kelvin waves (FK) 6-7 50-80 m/s ~ 20 km Ultrafast Kelvin waves (UFK) 3-4 100-120 m/s >40 km

Introduction

S Nonlinear interaction

The nonlinear interaction is pathway to short-term variability of the atmospheric tides. When a nonlinear interaction between a tide and planetary wave (PW) takes place (Teitelbaum and Vial, 1991):

S The tidal amplitude is modulated at the period of the

planetary wave;

S Generation of secondary waves with frequencies that

are the sum and difference between the frequencies of the primary waves (tide and PW).

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Instruments and Data

Meteor radar

Cariri (7.4°S, 36.5°W)

Photometer

Credit: Alisson Carvalho

Instruments and Data

S Photometer: nightly measurements of the integrated

intensities:

S OI557.7nm (green line), O2b(0-1) and OH(6-2) emissions; S OH rotational temperature;

Lomb-Scargle analysis

Instruments and Data

S Meteor radar

S Zonal and meridional winds

at: S 82; 85; 88; 91; 94; 98

km

S 2h resolution Operating frequency 35.24MHz Peak power 12kw

Results: wind 3-4 day oscillations

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Zonal wavelet spectrum at 91 km. Meridional wavelet spectrum at 91 km.

Results: wind 3-4 day oscillations

S 3-4 day filtered wind

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Well known UFKW. Their effects on the MLT and equatorial ionosphere have been addressed in several studies (e.g .Takahashi et al., 2007; Lima et al., 2008; Onohara et al., 2011).

~λv 40km

Phase (days)

• Ampl. (m/s)

Results: airglow 3-4 day

• scillations

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Normalized Lomb-Scargle periodogram.

The case of March 2005

S

The UFKW signature well characterized in the OH, O2 and TOH, but not in the OI557.7nm emission;

Egito et al., (2018)

Results: airglow 3-4 day

• scillations

S The 3-4 day oscillation in the airglow in March 2005.

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Why the UFKW signature is not mathematically

• bserved in the

OI557.7nm emission?

S May be related to

the influence of the atmospheric tides

Results: airglow 3-4 day

• scillations

S OI557.7nm (green line) nightly variation

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Tides are known for strongly affect the airglow. In the equatorial region the airglow is strongly driven by the diurnal tide specially before midnight (Shepherd et al., 2005)

Results: airglow 3-4 day

• scillations

S Post midnight data S (00:00 to 05:00LT)

S The 3-4 day UFKW signature is

well defined in all emissions, including the OI557.7nm.

S Short time (few days) variability

• f the tides may affect the

airglow variations associated to the UFKW.

S Nonlinear interaction

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Results: nonlinear interaction

S Generated secondary waves

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UFKW DT Secondary waves DT Secondary waves Sum and difference between frequencies of the primary waves (tides and PW)

Results: nonlinear interaction

S Tidal amplitude modulation

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Amplitude modulation

• f the diurnal tide

in the zonal wind at 3.5-day period.

Results: nonlinear interaction

S The 1.3-day secondary wave

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Downward phase progression:

• Upward propagation of

energy and momentum

• λv ~ 44 km

Summarizing

S We observed the presence of an UFKW in the airglow

and neutral wind;

S We found indications of the nonlinear interaction

between the UFKW and diurnal tide:

S The diurnal tide amplitude was found to be modulated by

the UFKW;

S A 1.3-day secondary wave was observed in the zonal wind

and it was found to propagate upward with a relatively long vertical wavelength (~44 km); S The nonlinear interaction, by changing the tidal

amplitudes, may have modified the observed airglow variability in the scale of days.

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Acknowledgements

S We are thankful to the ANGWIN organize committee for

providing financial support to our attendance at this workshop.

EGITO, F.; BURITI, Ricardo Arlen ; MEDEIROS, A. F. ; TAKAHASHI, H. . Ultrafast Kelvin waves in the MLT airglow and wind, and their interaction with the atmospheric tides. ANNALES GEOPHYSICAE, v. 36, p. 231-241, 2018.

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