The role of cyclone activity in snow accumulation on Arctic sea ice.

Identifying the mechanisms controlling the timing and magnitude of snow accumulation on sea ice is crucial for understanding snow's net effect on the surface energy budget and sea-ice mass balance. Here, we analyze the role of cyclone activity on the seasonal buildup of snow on Arctic sea ice using model, satellite, and in situ data over 1979-2016. On average, 44% of the variability in monthly snow accumulation was controlled by cyclone snowfall and 29% by sea-ice freeze-up. However, there were strong spatio-temporal differences. Cyclone snowfall comprised ~50% of total snowfall in the Pacific compared to 83% in the Atlantic. While cyclones are stronger in the Atlantic, Pacific snow accumulation is more sensitive to cyclone strength. These findings highlight the heterogeneity in atmosphere-snow-ice interactions across the Arctic, and emphasize the need to scrutinize mechanisms governing cyclone activity to better understand their effects on the Arctic snow-ice system with anthropogenic warming.

Mammography screening: how far is too far?

INTRODUCTION: This study answers the question: 'How far must a Canadian woman travel before the risk of a motor vehicle accident (MVA) outweighs the benefits of mammography screening?'. METHODS: Numbers needed to screen and false positive rates were extracted from information in the breast screening guidelines from the Canadian Task Force on screening for breast cancer. Motor vehicle accidents per billion vehicle kilometres were extracted from Transport Canada. The charts of women undergoing screening mammograms were reviewed to determine the average number of extra trips generated from a false positive mammogram. A formula was devised to determine when the distance travelled and risk of MVA outweighed the benefits of mammogram screening. RESULTS: How far a woman would need travel before the risk of that travel outweighed the benefits of screening mammography is determined by the province in which she lives (location) and her age. The distance of a round trip before the risk of travel outweighed the benefit of screening mammography varied from 65 km to 1151 km, according the patient's age and location. CONCLUSION: Travel risk is rarely discussed in recommending screening examinations. Nevertheless the benefits of screening can be outweighed by the risk of travel. Knowledge of travel risk is essential before recommending screening procedures.