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- Mitchell, Jonathan L., et al.
(författare)
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Locally enhanced precipitation organized by planetary-scale waves on Titan
- 2011
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Ingår i: Nature Geoscience. - : Springer Science and Business Media LLC. - 1752-0894 .- 1752-0908. ; 4:9, s. 589-592
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Tidskriftsartikel (refereegranskat)abstract
- Saturn's moon Titan exhibits an active weather cycle that involves methane(1-8). Equatorial and mid-latitude clouds can be organized into fascinating morphologies on scales exceeding 1,000 km (ref. 9). Observations include an arrow-shaped equatorial cloud that produced detectable surface accumulation, probably from the precipitation of liquid methane(10). An analysis of an earlier cloud outburst indicated an interplay between high-and low-latitude cloud activity, mediated by planetary-scale atmospheric waves(11). Here we present a combined analysis of cloud observations and simulations with a three-dimensional general circulation model of Titan's atmosphere, to obtain a physical interpretation of observed storms, their relation to atmosphere dynamics and their aggregate effect on surface erosion. We find that planetary-scale Kelvin waves arise naturally in our simulations, and robustly organize convection into chevron-shaped storms at the equator during the equinoctial season. A second and much slower wave mode organizes convection into southern-hemisphere streaks oriented in a northwest-southeast direction, similar to observations(9). As a result of the phasing of these modes, precipitation rates can be as high as twenty times the local average in our simulations. We conclude that these events, which produce up to several centimetres of precipitation over length scales exceeding 1,000 km, play a crucial role in fluvial erosion of Titan's surface.
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| 2. |
- Pithan, Felix, et al.
(författare)
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Role of air-mass transformations in exchange between the Arctic and mid-latitudes
- 2018
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Ingår i: Nature Geoscience. - : Springer Science and Business Media LLC. - 1752-0894 .- 1752-0908. ; 11:11, s. 805-812
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Forskningsöversikt (refereegranskat)abstract
- Pulses of warm and moist air from lower latitudes provide energy to the Arctic and form its main energy source outside of the summer months. These pulses can cause substantial surface warming and trigger ice melt. Air-mass transport in the opposite direction, away from the Arctic, leads to cold-air outbreaks. The outbreaks are often associated with cold extremes over continents, and extreme surface heat fluxes and occasional polar lows over oceans. Air masses advected across the strong Arctic-to-mid-latitude temperature gradient are rapidly transformed into colder and dryer or warmer and moister air masses by clouds, radiative and turbulent processes, particularly in the boundary layer. Phase changes from liquid to ice within boundary-layer clouds are critical in these air-mass transformations. The presence of liquid water determines the radiative effects of these clouds, whereas the presence of ice is crucial for subsequent cloud decay or dissipation, processes that are poorly represented in weather and climate models. We argue that a better understanding of how air masses are transformed on their way into and out of the Arctic is essential for improved prediction of weather and climate in the Arctic and mid-latitudes. Observational and modelling exercises should take an air-mass-following Lagrangian approach to attain these goals.
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| 3. |
- Shaw, T. A., et al.
(författare)
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Storm track processes and the opposing influences of climate change
- 2016
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Ingår i: Nature Geoscience. - 1752-0894 .- 1752-0908. ; 9:9, s. 656-664
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Forskningsöversikt (refereegranskat)abstract
- Extratropical cyclones are storm systems that are observed to travel preferentially within confined regions known as storm tracks. They contribute to precipitation, wind and temperature extremes in mid-latitudes. Cyclones tend to form where surface temperature gradients are large, and the jet stream influences their speed and direction of travel. Storm tracks shape the global climate through transport of energy and momentum. The intensity and location of storm tracks varies seasonally, and in response to other natural variations, such as changes in tropical sea surface temperature. A hierarchy of numerical models of the atmosphere-ocean system - from highly idealized to comprehensive - has been used to study and predict responses of storm tracks to anthropogenic climate change. The future position and intensity of storm tracks depend on processes that alter temperature gradients. However, different processes can have opposing influences on temperature gradients, which leads to a tug of war on storm track responses and makes future projections more difficult. For example, as climate warms, surface shortwave cloud radiative changes increase the Equator-to-pole temperature gradient, but at the same time, longwave cloud radiative changes reduce this gradient. Future progress depends on understanding and accurately quantifying the relative influence of such processes on the storm tracks.
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