Spatial Dependence of Floods Shaped by Spatiotemporal Variations in Meteorological and Land-Surface Processes

With in situ observations using acoustic Doppler current profilers (ADCPs) and numerical experiments using the Finite Volume Coastal Ocean Model (FVCOM), this study investigates atmospheric cold front induced exchange of water between Lake Pontchartrain Estuary and coastal ocean through multiple inlets. Results show that the sub-tidal hydrodynamic response is highly correlated with meteorological parameters. Northerly and westerly winds tend to push water out of Lake Pontchartrain, while south and east winds tend to produce currents flowing into it. For most cases, the sub-tidal water level is inversely correlated with the east wind, with the correlation coefficient being ∼ 0.8. The most important finding of this work is that, contrary to intuition, the cold front induced remote wind effect has the greatest contribution to the overall water level variation, while the local wind stress determines the surface slope inside the estuary. It is found that wind driven flow is roughly quasi-steady state: the surface slope in the north-south direction is determined by the north-south wind stress, explaining ∼ 83% of the variability but less so in the east-west direction (∼ 43%). In other words, the north-south local wind stress determines the water level gradient in that direction in the estuary while the overall water level change is pretty much controlled by the open boundary which is the "remote wind effect", a regional response that can be illustrated only by a numerical model for a much larger area encompassing the estuary.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2017JC012977

Cold Front Driven Flows Through Multiple Inlets of Lake Pontchartrain Estuary

This article describes results from a new four-year (2009–2012) radar-based precipitation climatology for the southeastern United States (SE USA). The climatology shows that a size-based classification between mesoscale precipitation features (MPF) and isolated precipitation reveals distinct seasonal and diurnal variability of precipitation. On average, from 70 to 90% of precipitation is associated with MPF, generally less in the summertime and in southern coastal regions. MPF precipitation has a relatively small seasonal cycle except in Florida and the warm offshore waters of the Gulf Stream. In contrast, isolated precipitation has a dramatic seasonal cycle that outlines the SE USA coastline whereas the MPF precipitation does not, consistent with a thermodynamic mechanism for onshore isolated storms in coastal regions. In summer, the isolated precipitation preferentially forms offshore at night, and dramatically ‘flips’ inland by early afternoon. In contrast, MPF precipitation has no clear diurnal variations except in the southern coastal region in the summer, likely associated with sea breeze convection organized on the mesoscale. These results suggest that the MPF versus isolated precipitation system framework provides a useful basis for future studies of large-scale and local controls on precipitation and resulting implications for long-range predictability of precipitation.

A seasonal and diurnal climatology of precipitation organization in the southeastern United States

Atmospheric mechanisms leading to the formation of very strong turbulent air–sea heat fluxes in the North Atlantic are analyzed using the National Centers for Environmental Prediction (NCEP...

/pdf/association-of-the-north-atlantic-surface-turbulent-heat-5emrz6jt0e.pdf

Association of the North Atlantic Surface Turbulent Heat Fluxes with Midlatitude Cyclones

Large-magnitude pressure signatures associated with a wide range of atmospheric phenomena (e.g., mesoscale gravity waves, convective complexes, tropical disturbances, and synoptic storm systems) are examined using a unique set of surface pressure sensors deployed as part of the National Science Foundation EarthScope USArray Transportable Array. As part of the USArray project, approximately 400 seismic stations were deployed in a pseudogrid fashion across a portion of the United States for 1–2 yr, then retrieved and redeployed farther east. Surface pressure observations at a sampling frequency of 1 Hz were examined during the period 1 January 2010–28 February 2014 when the seismic array was transitioning from the central to eastern continental United States. Surface pressure time series at over 900 locations were bandpass filtered to examine pressure perturbations on three temporal scales: meso- (10 min–4 h), subsynoptic (4–30 h), and synoptic (30 h–5 days) scales.Case studies of strong pressure pe...

Central and Eastern U.S. Surface Pressure Variations Derived from the USArray Network

The seasonal and interannual variability of the structure, evolution, and propagation of midlatitude cyclones in the southeast United States are studied using a composite analysis. In the upper levels, the composites show that the axis of the wintertime upper-level trough remains north–south oriented and propagates eastward along 40°N, while the summertime upper-level trough has a much slower propagation at a farther north latitude and an axis that is tilted in the northeast–southwest direction. Upper-level circulation changes are consistent with a shift from wintertime “cyclonic behavior” to summertime “anticyclonic behavior” midlatitude cyclones. Significant changes in the low-level structure and precipitation patterns of midlatitude cyclones ensue from these upper-level changes. While the winter composite is characterized by eastward-propagating midlatitude cyclones that extend deep into the subtropics, the summer composite is characterized by semistationary midlatitude troughs that only briefl...

http://myweb.ecu.edu/rickenbacht/Ferreira_etal_JClim_2013.pdf

A Climatology of the Structure, Evolution, and Propagation of Midlatitude Cyclones in the Southeast United States

Midlatitude cyclones that affected the Southeast (SE) United States between 1998 and 2010 were classified into five types according to their region of origin: (1) Continental United States, (2) Canadian, (3) Gulf Low, (4) Hatteras Low, or (5) Stationary. A composite analysis was used to examine differences in the structure, evolution, and propagation of these cyclones during boreal winter, when the largest number of cyclones affect the SE United States. Most of the midlatitude cyclones that affect the SE in the wintertime formed within the continental United States (∼11 events/winter), followed by Gulf Lows (∼4 events/winter) and Canadian cyclones (∼4 events/winter). Hatteras Lows were relatively rare (∼1 events/winter), and Stationary events did not occur during winter. While Canadian and Continental US cyclones occurred year-round the frequency of Gulf Low events peaked in the boreal winter when the upper-level jet was strongest and located further south. Hatteras Lows peaked in the boreal fall and winter, and Stationary events occurred almost exclusively during the boreal summer. Overall, Gulf Low and Continental US cyclones were the only cyclones that brought wintertime precipitation to the SE United States. When integrated over the season, Continental US cyclones made the largest contribution to the wintertime precipitation in the SE United States. On a per-event basis, however, Gulf Lows were the biggest wintertime precipitation makers in the SE United States while Canadian cyclones and Hatteras Lows did not bring much precipitation to the SE United States. Gulf Lows were more common during El Nino than La Nina years and tended to occur back-to-back with either another Gulf Low or with a Hatteras Low.

Linwood Earl Hall

Papers

A Climatology of the Structure, Evolution, and Propagation of Midlatitude Cyclones in the Southeast United States

Midlatitude cyclones in the southeastern United States: frequency and structure differences by cyclogenesis region