@article{14779, abstract = {The presence of a developed boundary layer decouples a glacier's response from ambient conditions, suggesting that sensitivity to climate change is increased by glacier retreat. To test this hypothesis, we explore six years of distributed meteorological data on a small Swiss glacier in the period 2001–2022. Large glacier fragmentation has occurred since 2001 (−35% area change up to 2022) coinciding with notable frontal retreat, an observed switch from down‐glacier katabatic to up‐glacier valley winds and an increased sensitivity (ratio) of on‐glacier to off‐glacier temperature. As the glacier ceases to develop density‐driven katabatic winds, sensible heat fluxes on the glacier are increasingly determined by the conditions occurring outside the boundary layer of the glacier, sealing the glacier's demise as the climate continues to warm and experience an increased frequency of extreme summers.}, author = {Shaw, Thomas E. and Buri, Pascal and McCarthy, Michael and Miles, Evan S. and Ayala, Álvaro and Pellicciotti, Francesca}, issn = {1944-8007}, journal = {Geophysical Research Letters}, keywords = {General Earth and Planetary Sciences, Geophysics}, number = {11}, publisher = {American Geophysical Union}, title = {{The decaying near‐surface boundary layer of a retreating alpine glacier}}, doi = {10.1029/2023gl103043}, volume = {50}, year = {2023}, } @article{10653, abstract = {Squall lines are known to be the consequence of the interaction of low-level shear with cold pools associated with convective downdrafts. Also, as the magnitude of the shear increases beyond a critical shear, squall lines tend to orient themselves. The existing literature suggests that this orientation reduces incoming wind shear to the squall line, and maintains equilibrium between wind shear and cold pool spreading. Although this theory is widely accepted, very few quantitative studies have been conducted on supercritical regime especially. Here, we test this hypothesis with tropical squall lines obtained by imposing a vertical wind shear in cloud resolving simulations in radiative convective equilibrium. In the sub-critical regime, squall lines are perpendicular to the shear. In the super-critical regime, their orientation maintain the equilibrium, supporting existing theories. We also find that as shear increases, cold pools become more intense. However, this intensification has little impact on squall line orientation.}, author = {Abramian, Sophie and Muller, Caroline J and Risi, Camille}, issn = {1944-8007}, journal = {Geophysical Research Letters}, number = {1}, publisher = {Wiley}, title = {{Shear-convection interactions and orientation of tropical squall lines}}, doi = {10.1029/2021GL095184}, volume = {49}, year = {2022}, } @article{12107, abstract = {The sensitivity of coarse-grained daily extreme precipitation to sea surface temperature is analyzed using satellite precipitation estimates over the 300–302.5 K range. A theoretical scaling is proposed, linking changes in coarse-grained precipitation to changes in fine-scale hourly precipitation area fraction and changes in conditional fine-scale precipitation rates. The analysis reveals that the extreme coarse-grained precipitation scaling with temperature (∼7%/K) is dominated by the fine-scale precipitating fraction scaling (∼6.5%/K) when using a 3 mm/h fine-scale threshold to delineate the precipitating fraction. These results are shown to be robust to the selection of the precipitation product and to the percentile used to characterize the extreme. This new coarse-grained scaling is further related to the well-known scaling for fine-scale precipitation extremes, and suggests a compensation between thermodynamic and dynamic contributions or that both contributions are small with respect to that of fractional coverage. These results suggest that processes responsible for the changes in fractional coverage are to be accounted for to assess the sensitivity of coarse-grained extreme daily precipitation to surface temperature.}, author = {Roca, Rémy and De Meyer, Victorien and Muller, Caroline J}, issn = {1944-8007}, journal = {Geophysical Research Letters}, number = {24}, publisher = {Wiley}, title = {{Precipitating fraction, not intensity, explains extreme coarse-grained precipitation Clausius-Clapeyron scaling with sea surface temperature over tropical oceans}}, doi = {10.1029/2022GL100624}, volume = {49}, year = {2022}, } @article{12588, abstract = {The thinning patterns of debris-covered glaciers in High Mountain Asia are not well understood. Here we calculate the effect of supraglacial ice cliffs on the mass balance of all glaciers in a Himalayan catchment, using a process-based ice cliff melt model. We show that ice cliffs are responsible for higher than expected thinning rates of debris-covered glacier tongues, leading to an underestimation of their ice mass loss of 17% ± 4% in the catchment if not considered. We also show that cliffs do enhance melt where other processes would suppress it, that is, at high elevations, or where debris is thick, and that they contribute relatively more to glacier mass loss if oriented north. Our approach provides a key contribution to our understanding of the mass losses of debris-covered glaciers, and a new quantification of their catchment wide melt and mass balance.}, author = {Buri, Pascal and Miles, Evan S. and Steiner, Jakob F. and Ragettli, Silvan and Pellicciotti, Francesca}, issn = {1944-8007}, journal = {Geophysical Research Letters}, keywords = {General Earth and Planetary Sciences, Geophysics}, number = {6}, publisher = {American Geophysical Union}, title = {{Supraglacial ice cliffs can substantially increase the mass loss of debris‐covered glaciers}}, doi = {10.1029/2020gl092150}, volume = {48}, year = {2021}, } @article{12604, abstract = {Glaciers in the high mountains of Asia provide an important water resource for millions of people. Many of these glaciers are partially covered by rocky debris, which protects the ice from solar radiation and warm air. However, studies have found that the surface of these debris-covered glaciers is actually lowering as fast as glaciers without debris. Water ponded on the surface of the glaciers may be partially responsible, as water can absorb atmospheric energy very efficiently. However, the overall effect of these ponds has not been thoroughly assessed yet. We study a valley in Nepal for which we have extensive weather measurements, and we use a numerical model to calculate the energy absorbed by ponds on the surface of the glaciers over 6 months. As we have not observed each individual pond thoroughly, we run the model 5,000 times with different setups. We find that ponds are extremely important for glacier melt and absorb energy 14 times as quickly as the debris-covered ice. Although the ponds account for 1% of the glacier area covered by rocks, and only 0.3% of the total glacier area, they absorb enough energy to account for one eighth of the whole valley's ice loss.}, author = {Miles, Evan S. and Willis, Ian and Buri, Pascal and Steiner, Jakob F. and Arnold, Neil S. and Pellicciotti, Francesca}, issn = {1944-8007}, journal = {Geophysical Research Letters}, keywords = {General Earth and Planetary Sciences, Geophysics}, number = {19}, pages = {10464--10473}, publisher = {American Geophysical Union}, title = {{Surface pond energy absorption across four Himalayan Glaciers accounts for 1/8 of total catchment ice loss}}, doi = {10.1029/2018gl079678}, volume = {45}, year = {2018}, } @article{9148, abstract = {Several observational studies have shown a tight relationship between tropical precipitation and column‐integrated water vapor. We show that the observed relationship in the tropics between column‐integrated water vapor, precipitation, and its variance can be qualitatively reproduced by a simple and physically motivated two‐layer model. It has previously been argued that features of this relationship could be explained by analogy with the theory of continuous phase transitions. Instead, our model explicitly assumes that the onset of precipitation is governed by a stability threshold involving boundary‐layer water vapor. This allows us to explain the precipitation‐humidity relationship over a broader range of water vapor values, and may explain the observed temperature dependence of the relationship.}, author = {Muller, Caroline J and Back, Larissa E. and O'Gorman, Paul A. and Emanuel, Kerry A.}, issn = {0094-8276}, journal = {Geophysical Research Letters}, keywords = {General Earth and Planetary Sciences, Geophysics}, number = {16}, publisher = {American Geophysical Union}, title = {{A model for the relationship between tropical precipitation and column water vapor}}, doi = {10.1029/2009gl039667}, volume = {36}, year = {2009}, }