The eastward component of the wind in the lower troposphere (850 hPa) simulated by an atmospheric model with roughly 50km horizontal grid.
(1 frame/6 hours for one full year, starting in January)
To help introduce myself, I’m starting with a post on a topic that I’ve been working on recently: the simulation of tropical cyclones in global atmospheric models.
Climate models are gradually moving to finer spatial resolution. Our lab is actively developing global atmospheric climate models with roughly 50 and 25 km grid spacing (even finer models are being run very experimentally), and there are a number of related efforts around the world. (In comparison, horizontal resolutions in most of the global atmospheric models referenced in the IPCC’s 4th assessment are of the order of 100-300km). The animation above is from a 50km model, and shows the lower tropospheric winds over a year of simulation. More precisely, it shows the east-west component of the wind vector (white => westerly –that is, from the west; black=> easterly) in the lower troposphere, on a constant pressure surface as is customary in meteorology. The actual surface protrudes above this level in places, especially the Tibetan plateau, and in those areas we use the near-surface wind instead, to avoid having to mark the data as missing in the animation. I like plotting the east-west (zonal) component like this, with a gray scale — it gives one the feeling of looking at a 3d contour map of sea-level pressure, lighted from the south in the Southern Hemisphere and from the north in the Northern Hemisphere (because the east-west component of the winds is closely related to the north-south gradient of the pressure).
I want to focus here, not on the dominant mid-latitude waves that are associated with the highs and lows and jet stream meanders familiar from weather maps, but the small isolated vortices that form in the tropics. These seem to develop in a variety of ways and have sizes that are not well-resolved by the grid. Do they correspond with anything in the real world?