infrasound technology workshop – tokyo, november 2007 1 listen to the sounds of the antarctic...

Infrasound Technology Workshop – Tokyo, November 2007 1

Listen to the Soundsof the

Antarctic Atmosphere

L. Ceranna, A. Le Pichon & E. Blanc

BGR / B3.11, Hannover, Germany

CEA / DASE, Bruyères-le-Châtel, France


Content

The Antarctic Infrasound Array I27DE

Observations and Signal Detections at I27DE

Conclusions

Future Work

• Design and Configuration• Noise Reduction and Performance

• Infrasound: Microbaroms and Mountain Associated Waves• Gravity Waves

• Neumayer III• Electric Power Generation using Wind Turbines• Reconfiguration of I27DE


Location of infrasound station I27DE

5°W10 °W

71 °S

72 °S

Satellite Image of the Ekström Ice Shelf


Site map of I27DE


Array responses for two 9-element configurations

‘Pinwheel‘ Configuration

Concentric Configuration Array Response

Array Response

Co-Array

Co-Array


Design and installation of hose arrays

16 arms: 90 and 70 m aperture




The effect of wind

Comparison of different noise levels depending on wind speed


Comparison of different noise levels depending on the rate ofsnow accumulation on top of the pipe arrays

Noise reduction by snow coverage


Array performance as a function of wind speed

PMCC analysis in frequency range from 0.05 to 4 Hz, Jan-2003 – Dec-2005

mb-signals, [0.05 0.7] Hz

detection threshold

hf-signals, [0.7 4.0] Hzdetection threshold


Detection of hf- and mb-signals, Mar-2003 – Sep-2007

~365,000 hf-detections, ~515,000-mb detections


Average radial stratospheric wind speeds, HWM-93

motion of ocean swells along peri-Antarctic belt


Amplitudes of mb-signals, Mar-2003 – Sep-2007


Trace velocities of mb-signals, Mar-2003 – Sep-2007


Amplitudes of mw-signals, Mar-2003 – Sep-2007

~41,000 mw-detections


Trace velocities of mw-signals, Mar-2003 – Sep-2007


Amplitudes of gw-signals, Mar-2003 – Sep-2007

~50,000 gw-detections


Trace velocities of gw-signals, Mar-2003 – Sep-2007


Example of gravity waves – bores at I27DE


Comparison of detected signals, August/September 2004

wind

microbaroms

mountain associated waves

gravity waves

infrasound

• mb and maw signals are (completely) decoupled• infrasound signals and gravity waves are not correlated• trace velocity of gw signals indicates limits of infrasound detection capability

maw: VT{gw} < 10 m/s; mb: VT{gw} < 20 m/s• are measured wind and gw signals correlated?!


Wave parameters of gravity waves and measured wind

β=82°±22°VT=17±7 m/sA=0.16 Pa β=238°±14°

VT=9±6 m/sA=0.09 Pa


I27DE has demonstrated that its configuration and design are well suited for high wind conditions. It has been operated for more than 4.5 years without any major problems. The average detection threshold of mb-signals can be estimated at wind speeds of 16 m/s, i.e., at almost 85 % of the time I27DE have the capability to detect infrasound signals showing typical mb-signal amplitudes.

Detection of mb-signals correlates well with a stable stratospheric duct obtained with HWM-93 showing easterly directions during the Antarctic summer (December & January) and westerly at other time of the year. An anomaly in the number of detections and trace velocity was observed for mb-signals during the Antarctic winter, the reason for probable absence of the stratospheric duct is currently not clear. mw-Signals are decoupled from mb detections in winter times, however regard during Antarctic summer mw detections are dominated by mb-signals. Moreover another source, being independent of stratospheric duct, exists in the direction of ~120°.

Conclusions I


gw-signals are showing large amplitudes (gwE: 0.16 Pa, gwW: 0.09 Pa). These signals are NOT correlated to the stratospheric duct. gw-signals are correlated to measured wind speed, both with respect to speed and direction. Infrasound signals (mb + mw) are not correlated with gravity waves. The trace velocity of gw-signals indicates limits of infrasound detection capability (mw: VT{gw} < 10 m/s; mb: VT{gw} < 20 m/s).

The data of all infrasound stations, especially those which are linked to the peri-Antarctic belt, should to be analyzed on a broad frequency range including gw-signals (50 – 500 s).

Conclusions II


Neumayer III research base

L*W*H 68*25*28 m3

height above snow 6 m

weight 2400 t

floor space 1900 m2

‘life-span’ 25 a

Neumayer III

L*D 120*9 m2 [2x]

depth below snow -5 → 15 m

floor space 2000 m2

‘life-span’ 16 a

Neumayer


Relocation of I27DE in 2008/09

• Neumayer III will be built ~5 km to south of the current Neumayer research base

• the construction work for the new research base will be started this year

• a close schedule has to be kept (note, vessels call at the station only twice a year)

• cables for power supply of I27DE will be laid out this Antarctic summer

• I27DE will be relocated 2008/2009 (if the PTS will hopefully realize that Neumayer is not just around the corner)


Electric Power Supply at Neumayer III

• 3 * 30-kW horizontal axis wind turbines (< 100 dB aerodynamic noise)• 3 blades, 30 rpm, 15 m tower height, and 5 m blade radius, BPH=1.5 Hz

catabatic winds: ~180°, wind speed ~ 4 m/seasterly winds: ~90°, wind speed ~ 6 m/s

58 dB

54 dB

infrasound technology workshop – tokyo, november 2007 1 listen to the sounds of the antarctic...

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