![]() While there is no requirement for a pilot to be able to identify every cloud type by name and classification, basic knowledge can mean the difference between a comfortable flight, and a dangerous one.Clouds are visible indications of atmospheric processes which provide clues on frontal activity and general weather patterns.This means that one can get low cloud over the Tibetan plateau, for example, because we are using there the same IFS model levels to divide up cloud layers that we use the over open ocean. * strictly pressure levels are not used, but actually the IFS model levels that correspond to the given pressure levels in a standard atmosphere. The degree of randomness in the overlap is dependant upon distance between layers. But note: the Total Cloud Cover (TCC) is cloud layers integrated from the top of the atmosphere down to the surface with overlap assumptions based upon global observations.Cloud integrated from 800hPa* down to the surface. Cloud integrated from 450hPa* down to 800hPa*. Cloud integrated from top of the atmosphere down to 450hPa*. The low, medium and high and total cloud cover for each grid column are calculated from the profile of the predicted cloud fraction using assumptions about the overlap between the subgrid clouds in the vertical (whether the layers of cloud are stacked above one another in the vertical, or whether they are displaced relative to one another).įig2.1.21: Example of Assessment of Cloud Cover. In contrast, the precipitation from the large scale cloud scheme has a finite fall speed and can be blown laterally by the wind across grid boxes during descent. However, the main part of the precipitation from the core of the updraught is treated diagnostically in the convection scheme, with the assumption that all the precipitation falls out within the grid column in a timescale less than the model timestep. The convection "detrains" cloud and precipitation to the large-scale cloud scheme, representing convective anvils and the precipitation associated with the more stratiform part of the convective cell. due to large-scale ascent or radiative cooling), but the two schemes are connected and represent different parts of the cloud and precipitation in a grid column. This is important for the “life history” of falling precipitation (from level-with-cloud to level-with-clear-sky and vice-versa) and this process may occur several times during the descent of the IFS model precipitation.Ĭonvection processes (due to subgrid-scale convective updraughts) are calculated separately from larger scale cloud processes (e.g. A cloud-overlap algorithm calculates the relative placement of clouds across IFS model levels. ![]() Users should check the analysed cloud against observations as far as possible in these circumstances (see also model boundary layer).įig2.1.20: Schematic diagram to illustrate the parameterised processes for precipitation and clouds within a single grid box. This has a corresponding effect on radiation balance at the surface and consequently also upon near-surface temperatures. Often there is uncertainty regarding the cloud extent, phase, thickness or persistence. One of these is stratiform cloud beneath an inversion, especially subsidence inversions in high pressure situations, which can be difficult for atmospheric models to both analyse and forecast. There are some meteorological situations that are more challenging to forecast than others. Only rain or snow is produced by the precipitation scheme and hail is not considered nor developed in the IFS model convection scheme, no matter how unstable is the IFS model atmosphere. convection limited to lower troposphere with stable moist layer above). Cloud processes such as condensation, evaporation, glaciation and precipitation formation in convective and stratiform clouds are all taken into account with physically-based equations.Ĭloud is parameterised within a grid box as stratiform or convective according to the stability or instability of the IFS model atmosphere but it is possible to have both types where convection does not extend throughout the IFS model troposphere (e.g. The IFS predicts the three-dimensional cloud field with three variables for each grid box cloud fraction, cloud liquid water and cloud ice.
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