Influence of the North Atlantic Subtropical High on wet and dry sea-breeze events in North Carolina, United States

Nicholas T Luchetti,Rosana Nieto Ferreira,Joel D Mcauliffe,Thomas M Rickenbach,Mark R Nissenbaum

doi:10.14198/ingeo2017.68.01

Nicholas T Luchetti, Rosana Nieto Ferreira + Show 3 more

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https://doi.org/10.14198/ingeo2017.68.01

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Abstract

The sea-breeze (SB) is an important source of summertime precipitation in North Carolina (NC, southeast United States). However, not all SB events produce precipitation. A climatology of wet and dry SB events in NC is used to investigate the conditions that are conducive to precipitation associated with the sea breeze. Radar imagery was used to detect 88 SB events that occurred along the NC coast between May-September of 2009-2012. The majority (85%) of SB events occurred during offshore flow (53%) or during flow that was parallel to the coast (22%). SB events were separated into dry (53%) and wet (47%) events and differences in the dynamic and thermodynamic parameters of the environment in which they formed were analyzed. Significant differences in dynamic and thermodynamic conditions were found. SB dry events occurred under stronger winds (6.00 ± 2.36 ms-1) than SB wet events (4.02 ± 2.16 ms-1). Moreover, during SB wet events larger values of convective available potential energy and lower values of convective inhibition were present, conditions that favor precipitation. Overall, the SB wet events accounted for 20-30% of the May-September precipitation along the NC coastal region. The position of the North Atlantic Subtropical High (NASH) controls both moisture availability and winds along the NC coast, thus providing a synoptic-scale control mechanism for SB precipitation. In particular, it was shown that when the NASH western ridge is located along the southeast coast of the United States, it causes a moist southwesterly flow along the NC coast that may favor the occurrence of SB wet events.

Highlights

Located in the subtropics along the east coast of the United States, North Carolina (NC, southeast United States) has a humid subtropical climate with mild winters and hot summers (e.g., Gil Olcina and Olcina Cantos, 2017)
The location of the North Atlantic Subtropical High (NASH) western ridge may be the overarching parameter that controls precipitation in the NC SB. Results from this SB climatology suggest that an interplay of optimal thermodynamic and synoptic-dynamic conditions must be present for a NC SB front to induce precipitation on any given SB day
This study shows that the best conditions for the NC SB to induce precipitation would occur with enhanced early morning instability, minimal stable air aloft and synoptic scale winds that are from the W-SW at about 4 ms-1

Summary

Introduction

Located in the subtropics along the east coast of the United States (figure 1), North Carolina (NC, southeast United States) has a humid subtropical climate with mild winters and hot summers (e.g., Gil Olcina and Olcina Cantos, 2017). The state is flanked by the Blue Ridge Mountains to the west and by the warm waters of the Gulf Stream to the east and is naturally divided into three major geographic regions: Mountains, Piedmont and Coastal Plains (figure 1). This geography creates significant east-west differences in the annual precipitation regimes of the mountainous west, central Piedmont and Coastal Plains (figure 2). Snow amounts vary from 25 mm (liquid equivalent) per year at the coast, to 250 mm in the Piedmont and 400 mm in the Mountains region with some high mountain peaks accumulating over 1200 mm of snowfall Its geographic location, protruding into the warm waters of the Gulf Stream and into the track of Atlantic tropical cyclones, makes North Carolina the state with the second highest number of tropical cyclone strikes in the country, right behind Florida (e.g., Larson, Zhou and Higgins, 2005; Shepherd, Grundstein and Mote, 2007)

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