Annual and Seasonal Surface Circulation over the Mid Atlantic Bight
Continental Shelf Derived from a Decade of High Frequency Radar
Observations
Abstract
A decade (2007-2016) of hourly 6 km resolution maps of the surface
currents across the Mid Atlantic Bight (MAB) generated by a
regional-scale High Frequency Radar network are used to reveal new
insights into the spatial patterns of the annual and seasonal mean
surface flows. Across the 10-year time series, temporal means, inter-
and intra-annual variability are used to quantify the variability of
spatial surface current patterns. The 10-year annual mean surface flows
are weaker and mostly cross shelf near the coast, increasing in speed
and rotating to more alongshore directions near the shelf break, and
increasing in speed and rotating to flow off-shelf in the southern MAB.
The annual mean surface current pattern is relatively stable year to
year compared to the hourly variations within a year. The ten-year
seasonal means exhibit similar current patterns, with winter and summer
more cross-shore while spring and fall transitions are more alongshore.
Fall and winter mean speeds are larger and correspond to when mean winds
are stronger and cross-shore. Summer mean currents are weakest and
correspond to a time when the mean wind opposes the alongshore flow.
Again, intra-annual variability is much greater than interannual, with
the fall season exhibiting the most interannual variability in the
surface current patterns. The extreme fall seasons of 2009 and 2011 are
related to extremes in the wind and river discharge events caused by
different persistent synoptic meteorological conditions, resulting in
more or less rapid fall transitions from stratified summer to well-mixed
winter conditions.