The seasonal evolution of albedo across glaciers and the surrounding landscape of Taylor Valley, Antarctica

The McMurdo Dry Valleys (MDVs) of Antarctica are a polar desert ecosystem consisting of alpine glaciers, ice-covered lakes, streams, and expanses of vegetation-free rocky soil. Because average summer temperatures are close to 0 ∘C, the MDV ecosystem in general, and glacier melt dynamics in particular, are both closely linked to the energy balance. A slight increase in incoming radiation or change in albedo can have large effects on the timing and volume of meltwater. However, the seasonal evolution or spatial variability of albedo in the valleys has yet to fully characterized. In this study, we aim to understand the drivers of landscape albedo change within and across seasons. To do so, a box with a camera, GPS, and shortwave radiometer was hung from a helicopter that flew transects four to five times a season along Taylor Valley. Measurements were repeated over three seasons. These data were coupled with incoming radiation measured at six meteorological stations distributed along the valley to calculate the distribution of albedo across individual glaciers, lakes, and soil surfaces. We hypothesized that albedo would decrease throughout the austral summer with ablation of snow patches and increasing sediment exposure on the glacier and lake surfaces. However, small snow events (<6 mm water equivalent) coupled with ice whitening caused spatial and temporal variability of albedo across the entire landscape. Glaciers frequently followed a pattern of increasing albedo with increasing elevation, as well as increasing albedo moving from east to west laterally across the ablation zone. We suggest that spatial patterns of albedo are a function of landscape morphology trapping snow and sediment, longitudinal gradients in snowfall magnitude, and wind-driven snow redistribution from east to west along the valley. We also compare our albedo measurements to the MODIS albedo product and found that overall the data have reasonable agreement. The mismatch in spatial scale between these two datasets results in variability, which is reduced after a snow event due to albedo following valley-scale gradients of snowfall magnitude. These findings highlight the importance of understanding the spatial and temporal variability in albedo and the close coupling of climate and landscape response. This new understanding of landscape albedo can constrain landscape energy budgets, better predict meltwater generation on from MDV glaciers, and how these ecosystems will respond to changing climate at the landscape scale.

The seasonal evolution of albedo across glaciers and the surrounding landscape of the Taylor Valley, Antarctica

The McMurdo Dry Valleys (MDVs) of Antarctica are a polar desert ecosystem consisting of alpine glaciers, ice-covered lakes, streams, and expanses of vegetation-free rocky soil. Because average summer temperatures are close to 0 °C, glacier melt dynamics in particular, but the Dry Valley ecosystem in general, are closely linked to the energy balance. A slight increase in incoming radiation or change in albedo can have large effects on the timing and volume of melt water. However, we have yet to fully characterize the seasonal evolution or spatial variability of albedo in the valleys. In this study, we aim to understand the drivers of landscape albedo change within and across seasons. To do so, we used a camera, gps, and short wave radiometer from a helicopter-based platform to fly transects 4–5 times a season along Taylor Valley over three seasons. We coupled these data with incoming radiation measured at 6 meteorological stations distributed along the valley to calculate the distribution of albedo across individual glaciers, lakes, and the soil surfaces. We hypothesized that albedo would decrease throughout the austral summer with ablation of snow patches and ice and increasing sediment exposure on the glacier and lake surfaces. However, small snow events (

Comments on initial conditions for the Abraham–Lorentz(–Dirac) equation

An accelerating electric charge coupled to its own electromagnetic field both emits radiation and experiences the radiation's reaction as a (self-)force. Considering the system from an Effective Field Theory perspective, and using the physical initial conditions of no incoming radiation can help resolve many of the problems associated with the often considered "notorious" Abraham–Lorentz/Abraham–Lorentz–Dirac equations.

Changes in seed weight in response to different sources: sink ratio in oilseed rape

Little knowledge exists about the degree of source, sink and source: sink limitations on mean seed weight in oilseed rape (Brassica napus L.). The objective of this work was to analyze the nature and magnitude on seed weight response to assimilate availability during the effective seed-filling period in oilseed rape. Three Argentinean varieties, Eclipse, Impulse, and Master, were grown under field conditions, and at the beginning of the effective seed filling period, a broad range of source: sink manipulation combinations were produced. Source manipulations consisted of two incoming radiation (R) level reductions: 0% (Rn) and ~50% (Rs) combined with three different sources: sink treatments were applied: C, control; PR, ~50% pod removal, and D, 100% defoliation. Rs significantly reduced yield (15%) and MSW (12%) with respect to Rn, without significant effects on the rest of the sub yield components. Source:sink manipulation treatments significantly affected all yield components. PR diminished yield by 29%, reducing ca. 40% seeds pl-1 by reductions pods pl-1 (41%) with respect to Rn, whereas PR increased MSW by 19%, counterbalancing the reduction in seeds pl-1 and thereby in yield. When considering different seed positions along the main raceme, Rs reduced MSW by 12% independently of seed positions onto the raceme. On the contrary, PR increased MSW in average 17% with respect to C. Results reported here suggest that oilseed rape has source: sink co-limitation during the effective seed filling period, which is apparently higher than wheat and lower than maize. DOI: http://dx.doi.org/10.3329/ijarit.v4i1.21091 Int. J. Agril. Res. Innov. & Tech. 4 (1): 44-52, June, 2014