Climatology of cloud-to-ground lightning in Georgia, USA, 1992-2003

A 12-year climatology of lightning cloud-to-ground flash activity for Georgia revealed the existence of three primary regions of high lightning activity: the area surrounding the Atlanta Metropolitan Statistical Area, east-central Georgia along the fall line, and along the Atlantic coast. Over 8.2 million ground flashes were identified during the climatology. July was the most active lightning month and December was the least active. Annual, seasonal, and diurnal distributions of cloud-to-ground flashes were also examined. These patterns illustrated the interacting effects of land cover, topography, and convective instability in enhancing lightning activity throughout Georgia. A synoptic analysis of the ten highest lightning days during the summer and winter revealed the importance of frontal boundaries in organizing convection and high lightning activity during both seasons. The prominence of convective instability during the summer and strong dynamical forcing in the winter was also found to lead to outbreaks of high lightning activity

Synoptic evolution of midwestern U.S. extreme dew point events

Eight Midwestern extremely high dew point events were examined with respect to their synoptic characteristics and evolution. Individual and composite analyses of events suggest that there exists three predominant features associated with extreme dew point events. In nearly all cases, the evolution of the synoptic environment includes the development and propagation of low pressure from the high plains through the upper Great Lakes. The low pressure increases and backs the surface winds acting to advect low-level moisture from eastern Nebraska, Iowa, Missouri eastward into Illinois and Indiana. The progression of the low pressure and attendant frontal boundaries also acts to modulate the length of the extreme low-level dew point event. Healthy crops and sufficient soil moisture content throughout this large agricultural region were also evident during the periods of extreme low-level moisture. Finally, the vertical thermal profile of the atmosphere during extreme dew point events supports previous findings and highlights the importance of restricted low-level mixing as instrumental in allowing near-surface moisture to become trapped and increased

Climatological Radar Delineation of Urban Convection for Atlanta, Georgia

The distribution of warm season (June through August) thunderstorm activity surrounding Atlanta, Georgia from 1997 to 2006 was determined utilizing composite reflectivity data obtained from the network of National Weather Service radars. The radar data, at 2 km and 5 min spatial and temporal resolutions, allows for high resolution analyses of urban convective trends when grid averaged over a 10-year period. Maxima of medium- to high-reflectivity episodes were identified to the north of and within downtown Atlanta and immediately east of the primary urban expansion of the central business district (CBD). Additional enhanced, high-reflectivity areas are found in southern Fulton and Clayton counties, located south of downtown Atlanta. These regions are also collocated with high-density urban expansion south of the Atlanta CBD. The research presented is the most comprehensive spatial and temporal analysis of grid averaged composite reflectivity data for urban convection conducted to date

Connectivity in coastal systems: Barrier island vegetation influences upland migration in a changing climate

Due to their position at the land–sea interface, barrier islands are vulnerable to both oceanic and atmospheric climate change-related drivers. In response to relative sea-level rise, barrier islands tend to migrate landward via overwash processes which deposit sediment onto the backbarrier marsh, thus maintaining elevation above sea level. In this paper, we assess the importance of interior upland vegetation and sediment transport (from upland to marsh) on the movement of the marsh–upland boundary in a transgressive barrier system along the mid-Atlantic Coast. We hypothesize that recent woody expansion is altering the rate of marsh to upland conversion. Using Landsat imagery over a 32 year time period (1984–2016), we quantify transitions between land cover (bare, grassland, woody vegetation, and marsh) and the marsh–upland boundary. We find that the Virginia Barrier Islands have both gains and losses in backbarrier marsh and upland, with 19% net loss from the system during the timeframe of the study and increased variance in marsh to upland conversion. This is consistent with recent work indicating a shift toward increasing rates of landward barrier island migration. Despite a net loss of upland area, macroclimatic winter warming resulted in 41% increase in woody vegetation in protected, low-elevation areas, introducing new ecological scenarios that increase resistance to sediment movement from upland to marsh. Our analysis demonstrates how the interplay between elevation and interior island vegetative cover influences landward migration of the boundary between upland and marsh (a previously underappreciated indicator that an island is migrating), and thus, the importance of including ecological processes in the island interior into coastal modeling of barrier island migration and sediment movement across the barrier landscape

Concurrent cloud-to-ground lightning and precipitation enhancement in the Atlanta, Georgia (USA) urban region

This study explores how the Atlanta, Georgia (United States), urban region influences warm-season (May through September) cloud-toground lightning flashes and precipitation. Eight years (1995–2003) of flashes from the National Lightning Detection Network and mean accumulated precipitation from the North American Regional Reanalysis model were mapped under seven different wind speed and direction combinations derived from cluster analysis. Overlays of these data affirmed a consistent coupling of lightning and precipitation enhancement around Atlanta. Maxima in precipitation and lightning shifted in response to changes in wind direction. Differences in the patterns of flash metrics (flash counts versus thunderstorm counts), the absence of any strong urban signal in the flashes of individual thunderstorms,and the scales over which flashes and precipitation enhancement developed are discussed in light of their support for land-cover- and aerosol-based mechanisms of urban weather modification. This study verifies Atlanta’s propensity to conjointly enhance cloud-to-ground lightning and precipitation production in the absence of strong synoptic forcing. However, because of variability in aerosol characteristics and the dynamics of land use change, it may be a simplification to assume that this observed enhancement will be persistent across all scales of analysis

Geomorphology and earth system science

Earth system science is an approach to obtain a scientific understanding of the entire Earth system on a global scale by describing how its component parts and their interactions have evolved, how they function, and how they may be expected to continue to evolve on all time-scales. The aim of this review is to introduce some key examples showing the role of earth surface processes, the traditional subject of geomorphology, within the interacting Earth system. The paper considers three examples of environmental systems in which geomorphology plays a key role: (i) links between topography, tectonics, and atmospheric circulation; (ii) links between geomorphic processes and biogeochemical cycles; and (iii) links between biological processes and the earth’s surface. Key research needs are discussed, including the requirement for better opportunities for interdisciplinary collaboration, clearer mathematical frameworks for earth system models, and more sophisticated interaction between natural and social scientists