Aerosol-precipitation interactions in the southern Appalachian Mountains

Abstract. There are many uncertainties associated with aerosol-precipitation interactions, particularly in mountain regions where a variety of processes at different spatial scales influence precipitation patterns. Aerosol-precipitation linkages were examined in the southern Appalachian Mountains, guided by the following research questions: (1) how do aerosol properties observed during precipitation events vary by season (e.g., summer vs. winter) and synoptic event type (e.g., frontal vs. non-frontal); and (2) what influence does air mass source region have on aerosol properties? Precipitation events were identified based on regional precipitation data and classified using a synoptic classification scheme developed for this study. Hourly aerosol data were collected at the Appalachian Atmospheric Interdisciplinary Research (AppalAIR) facility at Appalachian State University in Boone, NC (1110 m a.s.l., 36.215°, −81.680°). Backward air trajectories provided information on upstream atmospheric characteristics and source regions. During the warm season (June to September), greater aerosol loading dominated by larger particles was observed, while cool season (November to April) precipitation events exhibited overall lower aerosol loading with an apparent influence from biomass burning particles. Aerosol-induced precipitation enhancement may have been detected in each season, particularly during warm season non-frontal precipitation.

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Synoptic classification of 2009–2010 precipitation events in the southern Appalachian Mountains, USA

Climate Research ◽

10.3354/cr01116 ◽

2012 ◽

Vol 55 (1) ◽

pp. 1-15 ◽

Cited By ~ 11

Author(s):

GM Kelly ◽

LB Perry ◽

BF Taubman ◽

PT Soulé

Keyword(s):

Appalachian Mountains ◽

Synoptic Classification ◽

Southern Appalachian Mountains ◽

Southern Appalachian ◽

Precipitation Events

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Investigation of Atmospheric Rivers Impacting the Pigeon River Basin of the Southern Appalachian Mountains

Weather and Forecasting ◽

10.1175/waf-d-17-0060.1 ◽

2018 ◽

Vol 33 (1) ◽

pp. 283-299 ◽

Cited By ~ 8

Author(s):

Douglas K. Miller ◽

David Hotz ◽

Jessica Winton ◽

Lukas Stewart

Keyword(s):

North Carolina ◽

River Basin ◽

Large Scale ◽

Large Fraction ◽

Appalachian Mountains ◽

Warm Season ◽

Atmospheric Rivers ◽

Southern Appalachian Mountains ◽

Low Level ◽

Southern Appalachian

Abstract Rainfall observations in the Pigeon River basin of the southern Appalachian Mountains over a 5-yr period (2009–14) are examined to investigate the synoptic patterns responsible for downstream flooding events as observed near Knoxville, Tennessee, and Asheville, North Carolina. The study is designed to address the hypothesis that atmospheric rivers (ARs) are primarily responsible for the highest accumulation periods observed by the gauge network and that these periods correspond to events having a societal hazard (flooding). The upper 2.5% (extreme) and middle 33% (normal) rainfall events flagged using the gauge network observations showed that half of the heaviest rainfall cases were associated with an AR. Of those extreme events having an AR influence, over 73% had a societal hazard defined as minor-to-major flooding at the USGS river gauge located in Newport, Tennessee, or flooding observations for locations near the Tennessee and North Carolina border reported in the Storm Data publication. Composites of extreme AR-influenced events revealed a synoptic pattern consisting of a highly amplified slow-moving positively tilted trough, suggestive of the anticyclonic Rossby wave breaking scenario that sometimes precedes hydrological events of high impact. Composites of extreme non-AR events indicated a large-scale weather pattern typical of a warm season scenario in which an anomalous low-level cyclone, cut off far from the primary upper-tropospheric jet, was located in the southeastern United States. AR events without a societal hazard represented a large fraction (75%–88%) of all ARs detected during the study period. Synoptic-scale weather patterns of these events were fast moving and had weak low-level atmospheric dynamics.

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On High Winds and Foehn Warming Associated with Mountain-Wave Events in the Western Foothills of the Southern Appalachian Mountains

Weather and Forecasting ◽

10.1175/2008waf2007096.1 ◽

2009 ◽

Vol 24 (1) ◽

pp. 53-75 ◽

Cited By ~ 7

Author(s):

David M. Gaffin

Keyword(s):

Source Region ◽

Appalachian Mountains ◽

Return Flow ◽

Mountain Wave ◽

Mountain Waves ◽

Southern Appalachian Mountains ◽

Low Level ◽

Southern Appalachian ◽

Wave Induced ◽

High Winds

Abstract Extremely high winds of 40–49 m s−1 [90–110 miles per hour (mph)] were reported across the western foothills of the southern Appalachian Mountains on 22–23 December 2004, 17 October 2006, 24–25 February 2007, and 1 March 2007. The high winds in all four of these events were determined to be the result of mountain waves, as strong southeast winds became perpendicular to the mountains with a stable boundary layer present below 750 hPa and a veering wind profile that increased with height. Adiabatic warming of the descending southeasterly winds was also observed at the Knoxville airport during all four events (although of varying intensities), with the 850-hPa air mass immediately upwind of the Smoky Mountains determined to be the source region of these foehn winds. An interesting similarity among these four events was the location of the strongest 850-hPa winds northwest of the region, with a rapidly decreasing speed gradient observed over the mountains. These 850-hPa winds northwest of the mountains were also stronger than the 700-hPa winds in the region. It was hypothesized that strong low-level divergence developed in the foothills, as the stronger 850-hPa winds on the western side accelerated away from the mountains while the mountains prevented a rapid return flow from the eastern side. This low-level divergence likely helped to further strengthen the mountain-wave-induced mesolow and high winds in the western foothills. A 12-yr climatology of high wind events induced by mountain waves at Cove Mountain was also constructed. This climatology revealed that these events occurred primarily at night between November and March. Composite maps of mountain-wave events that produced warning-level and advisory-level winds revealed that an axis of stronger 850-hPa winds was typically located west of the mountains (away from the foothills). This finding (using reanalysis data instead of model data) further suggested that low-level divergence normally contributed to the intensity of mountain-wave-induced mesolows and winds in the western foothills of the southern Appalachian Mountains.

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