For my master’s thesis, I conducted research
on large-scale regime change and its effect on Northeast precipitation in the
cool season under the advisement of Dr. Lance Bosart and Dr. Dan Keyser. This work contributed to the CSTAR project, a cooperative
research effort of the University
at Albany and the Northeast
offices of the National Weather Service.
Research Summary:
Regimes and Northeast Precipitation
Northeast
precipitation, on average, is above normal during persistent (7 days or longer)
negative PNA regimes and persistent positive NAO regimes (graph).
Results also indicate that the PNA is often in a positive phase when
major 24-h cool-season precipitation events occur.
Regime Transitions and Northeast
Precipitation
Key
statistical results indicate that Northeast precipitation tends to be above
normal during cool-season transitions from a positive to negative North Atlantic
Oscillation (NAO) regime and, to a lesser extent, during cool-season
transitions from a negative to positive Pacific-North American (PNA)
regime. In addition, the probability of
a major 24-h cool-season precipitation event in the Northeast is enhanced during
these types of regime transitions.
Results also suggest that the NAO index typically decreases and the PNA
index typically increases surrounding the most significant cool-season
Northeast precipitation events. A
decreasing NAO index can be physically interpreted as a weakening of the
Composite analyses suggest that
surface cyclones associated with major Northeast precipitation events can
influence a change in the large-scale flow pattern from a positive to negative
NAO regime. Such cyclones track poleward
from the Northeast, transporting warm air to high latitudes over the North Atlantic. This process results in the eruption of a
ridge (blocking) near Greenland, a flow regime closely correlated to the
negative phase of the NAO pattern.