If a hurricane dies in the middle Atlantic, does it make a sound?

Desperate de jour – trying to locate unreported hurricanes prior to the satellite era by looking through old seismometer records in an attempt to prop up the imagined “global warming equals more hurricanes” connection….which we know doesn’t exist and has been debunked time and again. Most recently is was falsified  yesterday with FSU’s ACE graph, showing hurricane levels at a 30 year low.

From a Geological Society of America press release:

Seismic Noise Unearths Lost Hurricanes

Boulder, CO USA – Seismologists have found a new way to piece together the history of hurricanes in the North Atlantic – by looking back through records of the planet’s seismic noise. It’s an entirely new way to tap into the rich trove of seismic records, and the strategy might help establish a link between global warming and the frequency or intensity of hurricanes.

“Looking for something like hurricane records in seismology doesn’t occur to anybody,” said Carl Ebeling, of Northwestern University in Evanston. “It’s a strange and wondrous combination.”

The research is attempting to address a long-standing debate about whether the warming of sea-surface waters as a result of climate change is producing more frequent or more powerful hurricanes in the North Atlantic. It’s a tough question to answer.

Before satellite observations began in the 1960s, weather monitoring was spotty. Ships, planes, and land-based monitoring stations probably missed some hurricanes, which tend to last for about a week or so, Ebeling said. This type of uncertainty poses a problem for scientists, who can’t identify trends until they know what the actual numbers were.

To fill in the historical blanks, Ebeling and colleague Seth Stein are looking to seismic noise, an ever-present background signal that bathes the surface of the Earth. Seismic noise derives its energy from the atmosphere and then gets transmitted through the oceans into the solid earth, where it travels as waves. Seismometers record the noise as very low-amplitude wiggle patterns with much larger, obvious signals that come from earthquakes. Subtle changes in seismic noise frequency and amplitude have long been ignored.

Ebeling and Stein analyzed digital seismograms dating back to the early 90s from two monitoring stations: one in Harvard, Mass., and one in San Juan, Puerto Rico. For this study, the researchers looked at seismograms recorded during known hurricanes in an attempt to see whether patterns produced during hurricanes look predictably different from patterns produced during regular storms or when there are no storms at all.

Their preliminary results suggest that hurricanes do indeed produce recognizable patterns, and the waves generated by hurricanes travel large distances. The Harvard station recorded signals from Hurricane Andrew more than a thousand kilometers away.

“There’s definitely something there that shows this can be workable,” Ebeling said. “This is something new and interesting.”

At least one major hurdle remains before scientists will be able to pull together a complete hurricane history out of the seismic records. For most of the 20th century, seismograms recorded data on rolls of paper. Those records, which contain hundreds of thousands of hours of data, will need to be digitized. Ebeling is looking for an efficient way to do that.

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ABSTRACT:

View abstract at http://gsa.confex.com/gsa/2009AM/finalprogram/abstract_161903.htm.

EXTENDING THE NORTH ATLANTIC HURRICANE RECORD USING SEISMIC NOISE

EBELING, Carl W. and STEIN, Seth, Earth and Planetary Sciences, Northwestern University, 1850 Campus Drive, Evanston, IL 60208-2150, carl@earth.northwestern.edu

An ongoing debate within the climatological community centers on whether rising sea-surface temperatures due to global warming are changing the frequency or energy of North Atlantic hurricanes. The historical record makes it difficult to answer this question because before the advent of satellite-based observations in the 1960s, storms that did not make landfall may have gone unobserved, making an undercount likely.

To address this issue, we are developing a methodology to improve the record of the number and energy of North Atlantic hurricanes by analyzing their signals on decades of historical seismograms. Seismic noise—signals derived from natural sources and not related to earthquakes—is generated by atmospheric energy and so has been used as a proxy for oceanic wave climate and an indication of decadal-scale climate variability. Hence seismic noise should be usable to detect hurricanes that may have gone unobserved and to estimate their energy. As a first step in developing such a methodology, we are using digital data from the HRV (Harvard, MA) and SJG (San Juan, PR) seismic stations to calibrate seismic noise signals correlated with maximum wind speeds of well-characterized North Atlantic hurricanes and investigate the development of a hurricane discriminant.

Preliminary analysis of seismic noise power shows a variation by about two orders of magnitude between the low noise levels of the summer and the high noise levels between late September and May. Although a hurricane signature is not apparent in raw HRV power data, band-pass filtering of data recorded during hurricane Andrew (August 1992) reveals a signal correlatable with Andrew’s maximum storm wind speed. Because non-hurricane storms also generate signals in this band, we are investigating a discrimination algorithm combining data from the two distant sites.