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Creators/Authors contains: "Smith, James A."

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  1. Abstract

    Understanding the recent history of Thwaites Glacier, and the processes controlling its ongoing retreat, is key to projecting Antarctic contributions to future sea-level rise. Of particular concern is how the glacier grounding zone might evolve over coming decades where it is stabilized by sea-floor bathymetric highs. Here we use geophysical data from an autonomous underwater vehicle deployed at the Thwaites Glacier ice front, to document the ocean-floor imprint of past retreat from a sea-bed promontory. We show patterns of back-stepping sedimentary ridges formed daily by a mechanism of tidal lifting and settling at the grounding line at a time when Thwaites Glacier was more advanced than it is today. Over a duration of 5.5 months, Thwaites grounding zone retreated at a rate of >2.1 km per year—twice the rate observed by satellite at the fastest retreating part of the grounding zone between 2011 and 2019. Our results suggest that sustained pulses of rapid retreat have occurred at Thwaites Glacier in the past two centuries. Similar rapid retreat pulses are likely to occur in the near future when the grounding zone migrates back off stabilizing high points on the sea floor.

  2. Abstract

    Recent climate modeling studies point to an increase in tropical cyclone rainfall rates in response to climate warming. These studies indicate that the percentage increase in tropical cyclone rainfall rates often outpaces the increase in saturation specific humidity expected from the Clausius-Clapeyron relation (~7% °C−1). We explore the change in tropical cyclone rainfall rates over all oceans under global warming using a high-resolution climate model with the ability to simulate the entire intensity spectrum of tropical cyclones. Consistent with previous results, we find a robust increase of tropical cyclone rainfall rates. The percentage increase for inner-core tropical cyclone rainfall rates in our model is markedly larger than the Clausius-Clapeyron rate. However, when the impact of storm intensity is excluded, the rainfall rate increase shows a much better match with the Clausius-Clapeyron rate, suggesting that the “super Clausius-Clapeyron” scaling of rainfall rates with temperature increase is due to the warming-induced increase of tropical cyclone intensity. The increase of tropical cyclone intensity and environmental water vapor, in combination, explain the tropical cyclone rainfall rate increase under global warming.

  3. Abstract. Catchment-scale hydrological studies on drylands are lacking because of thescarcity of consistent data: observations are often available at the plotscale, but their relevance for the catchment scale remains unclear. Adatabase of 24 years of stream gauge discharge and homogeneoushigh-resolution radar data over the eastern Mediterranean allows us to describe the properties of floods over catchments spanning from desert toMediterranean climates, and we note that the data set is mostly of moderateintensity floods. Comparing two climatic regions, desert and Mediterranean,we can better identify specific rainfall-runoff properties. Despite the large differences in rainfall forcing between the two regions, the resulting unitpeak discharges and runoff coefficients are comparable. Rain depth andantecedent conditions are the most important properties to shape floodresponse in Mediterranean areas. In deserts, instead, storm core propertiesdisplay a strong correlation with unit peak discharge and, to a lesser extent,with runoff coefficient. In this region, an inverse correlation with meancatchment annual precipitation suggests also a strong influence of localsurface properties. Preliminary analyses suggest that floods in catchmentswith wet headwater and dry lower section are more similar to desertcatchments, with a strong influence of storm core properties on runoffgeneration.