The effects of storm surge and sea-level rise have become topics of everyday conversation in the days and weeks following Hurricane Sandy's catastrophic landfall along the mid-Atlantic coast.
Ongoing research by professor John Brubaker of the Virginia Institute of Marine Science is throwing light on another, less-familiar component of sea-level variabilitythe "intra-seasonal" changes that occupy the middle ground between rapid, storm-related surges in sea level and the long-term increase in sea level due to global climate change.
"These are cases when the water is just 'running high,'" says Brubaker, "but not from an obvious direct cause of a storm. It isn't necessarily windy, it's just an elevated water level without a clear cause."
Intra-seasonal variabilitywhich Brubaker says takes place on time-scales of 10 to 90 days and can add or detract a foot or more from the predicted tideis likely due to shifts in oceanic currents and large-scale movements of water masses along the coast. It often goes unacknowledged in discussions of sea-level trends, but can play an important role in water-level forecasts, coastal activities, and ecosystem health.
"Intra-seasonal variability has significant impacts," says Brubaker. "For instance, being aware of these non-tidal, non-storm anomalies is very important for forecasting. If you're experiencing a relative high during the approach of a storm, with water levels already elevated by a foot or more above predicted tides, that could make a big difference in terms of storm surge and coastal flooding."
Brubaker, who teams with researchers John Boon and David Forrest on the Tidewatch Forecast system at VIMS, says the Tidewatch forecasts account for at least some part of intra-seasonal variability by using as their starting point a moving average of the most recent 30 days of sea-level measurements. Other forecasts use mean sea level, a tidal datum that NOAA defines as the average measur
|Contact: David Malmquist|
Virginia Institute of Marine Science