Surface Pressure Fluctuations Produced by the Total Solar Eclipse of - - PowerPoint PPT Presentation

Surface Pressure Fluctuations Produced by the Total Solar Eclipse of 1 August 2008

Marty J.1, Dalaudier F.2, Ponceau D.3, Blanc E.3, Munkhuu U.4

1 CTBTO, Vienna, Austria 2 LATMOS, IPSL, UPMC‐Paris 6, France 3 CEA, DIF, DAM, Arpajon, France 4 RCAG, Ulaanbaatar, Mongolia

Chimonas (1970), Fritts and Luo (1993) Wake Moon shadow Troposphere Stratosphere Mesosphere IR UV

H2O O3

Heating rate profile [K.day‐1] Pressure height [km]

Bow-Wave Model Theory

Previous Observations

Distance from central line of the eclipse [km] Wave Period 10 min 20 min 1 h 2 h 4 h 50 100 500 1000 5000 10000

Venkatachari et al. (1982) Jones et al. (1992) Schödel et al. (1973) Beckman et Clucas (1973) Jones (1976) Jones (1999) Anderson et Keefer (1975) Jones et Bogart (1975) Anderson et al. (1972)

8 h 16 h

Farges et al. (2003) Seykora et al. (1985) Goodwin et Hobson (1978) Possible detection False detection No detection

Julien Marty Ph.D. defense

Can the passage of a solar eclipse produce detectable surface pressure fluctuations?

12 October 2010

An Unsolved Problem

• Are the existing models realistic enough ?
• Are the pressure fluctuations too small to be detected at the ground ?
• Are the measurement systems adapted to the expected signals ?
• Is the recording duration too short to differentiate the waves produced by the solar

eclipse from other waves ?

Observations <‐> Modeling

Period Amplitude [Pa] 0.1 1 10 100 10 min 20 min 1 h 2 h 4 h 10 h

Farges et al. (2003) Seykora et al. (1985) Goodwin et Hobson (1978) Model – Chimonas (1970)

Model description

• Linear spectral model (Fourier Transform) ‐> Constant dispersion relation parameters
• Propagation of normalized pressure fluctuation (amplitude do not depend on altitude)
• Linearization of fundamental fluid equations without source term (Fritts, 2003) :

1

• 1
• with

and

• 2

1 1 4

• Fully compressible dispersion relation for gravity waves

Normalized Exponential growth with altitude

φ′ , , , ′ , , ,

• /

Buoyancy frequency Coriolis parameter Sound velocity Density scale height

. exp 2

with

, ,

and

.

New Linear Spectral Numerical Model

Source effects Model benefits

Source spatial and temporal evolution Linearity Light (programming and calculation time) Wave field phase Wave perturbation variables (polarization equations) Ground reflection

• J. Marty and F. Dalaudier, 2010: Linear spectral numerical model for internal gravity wave propagation.
• J. Atmos. Sci., 67:1632–1642.
• Free propagation : wavefield can be directly estimated at any time
• Impulsive source : instantaneously modify the solution
• Continuous source : source terms are time‐discretized and handled as impulsive

modifications of the solution

New Linear Spectral Numerical Model

Fritts and Luo (1993) Marty and Dalaudier (2010) z= 80km, w’ [cm.s‐1], Δw’ = 0.05 z= 80km, w’ [cm.s‐1], Δw’ = 0.1

Stationary solutions Shape and intensity of the wavefield fairly similar Asymptotic solution reached after 40 h → Solar eclipses only last 2‐3 h at Earth’s surface

Eckermann et al. (2007) z= 80km, w’ [cm.s‐1]

Solutions in good agreement despite the use of constant atmospheric parameters

Marty and Dalaudier (2010) z= 80km, w’ [cm.s‐1]

Model Comparison - Stratospheric Source

Eckermann et al. (2007)

The main surface pressure perturbation cannot be explained by the stratospheric cooling The tropospheric cooling is likely to be the predominant source

Marty and Dalaudier (2010) with stratospheric source P [Pa] Marty and Dalaudier (2010) with tropospheric source P [Pa]





Surface Pressure Fluctuation

(320 km) (70 km) (1650 km) (200 km) (1060 km)

Total Solar Eclipse of 1 August 2008

Expected period for the tropospheric source Expected period for the stratospheric source

Expected Wave Periods

Distance from central line of the eclipse [km] Wave Period 10 min 20 min 1 h 2 h 4 h 50 100 500 1000 5000 10000

Venkatachari et al. (1982) Jones et al. (1992) Schödel et al. (1973) Beckman et Clucas (1973) Jones (1976) Jones (1999) Anderson et Keefer (1975) Jones et Bogart (1975) Anderson et al. (1972)

8 h 16 h

Farges et al. (2003) Seykora et al. (1985) Goodwin et Hobson (1978) Possible detection False detection No detection

Objectives

• Study the response of infrasound measurement systems in the gravity wave frequency band
• Characterize gravity events and identify sources (network operational for 20 days)
• Detect the pressure fluctuations produced by the passage of the 1 August 2008 solar eclipse

(determine source, propagation mode and spatial and temporal evolution)

Sonic anemometer External temperature 8 m 50 km

Mongolia 2008 (M2008) Measurement Campaign

• In case M2008 experiment, sensor less

protected from temperature variations

• MicrobarometerTS < 10 Pa.K‐1
• Thermal susceptibility (TS) can affect

pressure signals in the low‐frequency part of the GW band Need to correct pressure signals from influence of temperature

25 dB > 30 dB B1 TS = 2.8 Pa.K‐1

Validity of Pressure Measurements in GW Frequency Band ?

The sensor self‐noise, thermal susceptibility and transfer function do not significantly affect the pressure signals in the gravity wave frequency band

• J. Marty, D. Ponceau, and F. Dalaudier, 2010: Using the International Monitoring System infrasound network to study

gravity waves, Geophys. Res. Lett., 37, L19802. Buoyancy period Acoustic cut‐off period Infrasonic waves Gravity waves 8 min 5 min Period 0.05 s ~17 h Coriolis period 50 s 0.25 s IMS band 100 s Cut‐off period of pressure sensors

T : 14 → 30°C (steps = 2°C) T ≈ 19°C Temperature sensors used during M2008 campaign Calibrated temperature sensors Microbarometers used during M2008 campaign

Experimental protocol to improve TS estimation Evaluation of the correction

RSD: 17.4 % Raw signal RSD : 6.1 % Corrected with manufacturer TS RSD: 2.3 % Corrected with re‐evaluated TS

Excellent correction from temperature effects Manufacturer TS estimated linearly from 2 measures at ‐25°C and 60°C

Thermal Susceptibility Correction

Diurnal + semidiurnal oscillation (Superimposed epoch method) Cubic spline smoothing (meteorological changes) total eclipse time eclipse signal obtained from model (tropospheric source)

Pressure Signal Analysis

• Wavelet transform (Morlet) applied on a Fourier transform normalized by a factor

corresponding to the spectrum slope

Signal obtained from the model (stratospheric source x 20) Signal obtained from the model (tropospheric source x 3)

• Detection of two wave packets with similar time‐frequency characteristics to those
• btained from model

total eclipse time Ballard et al. (1969) Quiroz et Henry (1973) Randhawa (1974) Schmidlin et Olsen (1984)

Time-Frequency Analysis

IMS Data Analysis

Comparison With Previous Observations

• Development of a new linear spectral numerical model to simulate the propagation of

internal gravity waves

• Field experiment with broadband, high dynamic range and calibrated measurement systems
• Characterization of sensor response and susceptibility to environment
• Use of specific and original signal processing techniques
• Validation and use of IMS Infrasound data down to 24 h‐period
• J. Marty, F. Dalaudier, D. Ponceau, E. Blanc, U. Munkhuu, 2013: Surface Pressure Fluctuations Produced by the Total Solar

Eclipse of 1 August 2008. J. Atmos. Sci., 70, 809–823.

• J. Marty, D. Ponceau, and F. Dalaudier, 2010: Using the International Monitoring System infrasound network to study gravity

waves, Geophys. Res. Lett., 37, L19802.

• J. Marty and F. Dalaudier, 2010: Linear spectral numerical model for internal gravity wave propagation. J. Atmos. Sci.,

67:1632–1642.

Conclusion

A Unique Result

• The tropospheric cooling is the predominant source of surface pressure fluctuations after

the passage of a solar eclipse

• Worldwide detection of wave packets after the passage of the 1 August 2008 solar eclipse

with similar time‐frequency characteristics as those obtained from modeling

Thanks for your attention !