Search Results
You are looking at 1 - 2 of 2 items for :
- Author or Editor: Ankur R. Desai x
- Journal of Climate x
- Refine by Access: All Content x
Abstract
A relationship between midlatitude cyclone (MLC) tracks and snow-cover extent has been discussed in the literature over the last 50 years but not explicitly analyzed with high-resolution and long-term observations of both. Large-scale modeling studies have hinted that areas near the edge of the snow extent support enhanced baroclinicity because of differences in surface albedo and moisture fluxes. In this study, the relationship between snow-cover extent and midlatitude disturbance (MLD) trajectories is investigated across North America using objectively analyzed midlatitude disturbance trajectories and snow-cover extent from the North American Regional Reanalysis (NARR) for 1979–2010. MLDs include low-level mesoscale disturbances through midlatitude cyclones. A high-resolution MLD database is developed from sea level pressure minima that are tracked through subsequent 3-h time steps, and a simple algorithm is developed that identified the southern edge of the snow-cover extent. A robust enhanced frequency of MLDs in a region 50–350 km south of the snow-cover extent is found. The region of enhanced MLD frequency coincides with the region of maximum low-level baroclinicity. These observations support hypotheses of an internal feedback in which the snow-cover extent is leading the disturbance tracks through surface heat and moisture fluxes. Further, these results aid in the understanding of how midlatitude disturbance tracks may shift in a changing climate in response to snow-cover trends.
Abstract
A relationship between midlatitude cyclone (MLC) tracks and snow-cover extent has been discussed in the literature over the last 50 years but not explicitly analyzed with high-resolution and long-term observations of both. Large-scale modeling studies have hinted that areas near the edge of the snow extent support enhanced baroclinicity because of differences in surface albedo and moisture fluxes. In this study, the relationship between snow-cover extent and midlatitude disturbance (MLD) trajectories is investigated across North America using objectively analyzed midlatitude disturbance trajectories and snow-cover extent from the North American Regional Reanalysis (NARR) for 1979–2010. MLDs include low-level mesoscale disturbances through midlatitude cyclones. A high-resolution MLD database is developed from sea level pressure minima that are tracked through subsequent 3-h time steps, and a simple algorithm is developed that identified the southern edge of the snow-cover extent. A robust enhanced frequency of MLDs in a region 50–350 km south of the snow-cover extent is found. The region of enhanced MLD frequency coincides with the region of maximum low-level baroclinicity. These observations support hypotheses of an internal feedback in which the snow-cover extent is leading the disturbance tracks through surface heat and moisture fluxes. Further, these results aid in the understanding of how midlatitude disturbance tracks may shift in a changing climate in response to snow-cover trends.
Abstract
Expansion of agricultural lands and inherent variability of climate can influence the water cycle in the Amazon basin, impacting numerous ecosystem services. However, these two influences do not work independently of each other. With two once-in-a-century-level droughts occurring in the Amazon in the past decade, it is vital to understand the feedbacks that contribute to altering the water cycle. The biogeophysical impacts of land cover change within the Amazon basin were examined under drought and pluvial conditions to investigate how land cover and drought jointly may have enhanced or diminished recent precipitation extremes by altering patterns and intensity. Using the Weather Research and Forecasting (WRF) Model coupled to the Noah land surface model, a series of April–September simulations representing drought, normal, and pluvial years were completed to assess how land cover change impacts precipitation and how these impacts change under varied rainfall regimes. Evaporative sources of water vapor that precipitate across the region were developed with a quasi-isentropic back-trajectory algorithm to delineate the extent and variability that terrestrial evaporation contributes to regional precipitation. A decrease in dry season latent heat flux and other impacts of deforestation on surface conditions were increased by drought conditions. Coupled with increases in dry season moisture recycling over the Amazon basin by ~7% during drought years, land cover change is capable of reducing precipitation and increasing the amplitude of droughts in the region.
Abstract
Expansion of agricultural lands and inherent variability of climate can influence the water cycle in the Amazon basin, impacting numerous ecosystem services. However, these two influences do not work independently of each other. With two once-in-a-century-level droughts occurring in the Amazon in the past decade, it is vital to understand the feedbacks that contribute to altering the water cycle. The biogeophysical impacts of land cover change within the Amazon basin were examined under drought and pluvial conditions to investigate how land cover and drought jointly may have enhanced or diminished recent precipitation extremes by altering patterns and intensity. Using the Weather Research and Forecasting (WRF) Model coupled to the Noah land surface model, a series of April–September simulations representing drought, normal, and pluvial years were completed to assess how land cover change impacts precipitation and how these impacts change under varied rainfall regimes. Evaporative sources of water vapor that precipitate across the region were developed with a quasi-isentropic back-trajectory algorithm to delineate the extent and variability that terrestrial evaporation contributes to regional precipitation. A decrease in dry season latent heat flux and other impacts of deforestation on surface conditions were increased by drought conditions. Coupled with increases in dry season moisture recycling over the Amazon basin by ~7% during drought years, land cover change is capable of reducing precipitation and increasing the amplitude of droughts in the region.
