Hans in stormy weather

(the Onsala superconducting gravimeter has Hans as a nickname)

Two examples: A storm in the Norwegian Sea Sep. 08-10, 2009, and a storm sequence on the North Atlantic first week in November, 2009.

We show: a running spectrum of microseims between 512 and 2 seconds period to the left. To the right you see Significant Waveheight (ECMFW Wavemodel Analysis), blue indicating high waves.
During the period of the first days in November 2009 (3 to 9) storms were particularly active in the North Atlantic, patterns repeating as the wave height region moves from south of Greenland into the Bay of Biscaya. The microseimic level rises when the wavefield hits the shelf west or southwest of Ireland. The small charts show the wavefields at the synoptic times UT 0:00 6:00 12:00 and 18:00 each day, the larger-size charts the situation at noon each day, except at 0:00 on the first and at 18:00 on the last day. The storm-generated microseisms seem to go up in peak frequency when the waves progress into shallower water.
(Eventual stripes with spectral energy concentrated around 20 s are due to earthquakes).

This diagram shows the signal RMS (tides and barometric effects subtracted and short-period signal enhanced with a simple difference filter)

Norwegian Sea 2009-09-08 -- 10

The dip around noon Sep. 9: This was "my first storm", so before identifying the reason for the large increase of the noise I suspected malfunction of the gravimeter. During a few hours I turned he feedback amplification down, which caused a more sluggish response, attenuating the high