The coupling between clouds and circulation has long been recognised both as an essential aspect of tropical circulations as the circulations that accompany clouds are also known to play a role in their spatial organization. For example, mesoscale circulations driven by the heating contrast between convecting and non-convecting regions can drive moisture aggregation in the convecting...
Mesoscale Convective Systems (MCS) are common over Europe during the warm season (Morel and Senesi, 2002b) and are able to produce severe weather such as extreme precipitation leading to flash floods (Fiori et al., 2014). Studies analyzing the climatological characteristics of MCS over Europe are rare and were often based on only a few years of data or were focused on a limited area of Europe....
Land surface conditions can influence the onset and strength of convective systems. This is because sharp gradients in land surface properties result in differential latent and sensible heat fluxes, which leads to the development of mesoscale atmospheric circulations similar to the circulations present in land-sea breezes. These mesoscale circulations play an important roll in controlling the...
Increases in atmospheric water vapor holding capacity with temperature (7% K−1–8% K−1, CC-rate) can lead to increasing extreme precipitation (EP). Observations show that tropical EP has increased during the last five decades with a rate higher than in the extratropics. Global climate models (GCM's) diverge in the magnitude of increase in the tropics, and cloud-resolving models (CRM's) indicate...
Studies on the self-aggregation of convection have identified key physical mechanisms which drive and then maintain aggregation in a range of idealised radiative-convection equilibrium (RCE) models. These models are typically run without any land, rotation, variation in sea-surface temperatures (SSTs), or a diurnal cycle. Therefore, a key recurring question is how these convective processes...
Mixed-phase clouds play an important role in the Arctic climate system. However, accurate climate projections are seriously hampered due to uncertainties in representing these clouds. Understanding their dynamical behavior based on first principles is a challenging task which requires the disentanglement of mixed-phase micro-physical complexities and a multitude multitude of...
Mesoscale convective systems (MCSs) are organized clusters of thunderstorms spanning more than 100 km horizontally, persisting often for multiple hours. They are known to be the dominant source of rainfall in the tropics, and the longest-lived MCSs are shown to be largely responsible for tropical extreme precipitation [Roca and Fiolleau, 2020]. Globally, the most extreme storms tend to be...
It has been suggested that larger coldpool radii can delay the onset of convective self-aggregation. We demonstrate that coldpool characteristics can differ between 5 of the commonly microphysical schemes used by the WRF-model. We systematically increase/decrease coldpool size by changing the evaporation of rain to observe the impact on organization. One complication in interpreting these...
With a resolution of 2.5km, HARMONIE-AROME is a NWP model that roughly resolves deep convection. It is not clear if such a model should be capable of resolving open cell convection, as can be observed above sea under unstable conditions (e.g. during a cold air outbreak). However, especially the rain associated with this type of convection, can be important if it occurs with temperatures around...
Cold-air outbreaks off of the eastern US seaboard provide dramatic visual examples of cloud morphological transitions from closed-cell to more open-celled circulations. Space-based lidar and radar indicate the transitions typically involve mixed-phase clouds and precipitation, but may also remain liquid-only at times. Because the air flow moves over the Gulf Stream, significant surface...
Squall lines are the consequence of the interaction of low-level shear with cold pools associated with convective downdrafts, and beyond a critical shear, squall lines tend to orient themselves. It has been shown that this orientation has the effect of reducing the incoming wind shear to the squall line and maintains equilibrium between wind shear and cold pool spreading (Abramian et al...
A new generation of operational atmospheric models operating at horizontal resolutions in the range 200 m up to ~ 2 km is becoming increasingly popular for operational use in numerical weather prediction and climate applications. Such grid spacings are becoming sufficiently fine to resolve a fraction of the turbulent transports. Here we analyze LES results of a convective boundary layer...
CoMorph is a new mass-flux convection scheme, developed at the Met Office as part of the ParaCon programme. We report on the organisation that results with this scheme across a range of scales and forcings, and the key controls on the emergent structures that form.
