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Atmospheric dynamics explainers, with live forecasts
The diagnostics behind this site's circulation and stratosphere products, each explained with its equations and shown with its current forecast. They are written for meteorologists and students who want to know what a chart is measuring before trusting it.
- Eliassen–Palm flux and E–P flux divergence
What the Eliassen–Palm (E–P) flux and its divergence measure, how to read an E–P cross-section, and a live 15-day AIFS-ENS forecast of E–P flux and wave driving of the zonal-mean flow.
- Mountain torque and friction torque
How mountain and friction torques exchange angular momentum between the solid Earth and the atmosphere, the equations, how to read torque maps, and live AIFS-ENS forecasts of both torques by mountain range.
- Atmospheric angular momentum (AAM)
What atmospheric angular momentum measures, why it tracks El Niño and the length of day, the Global Wind Oscillation phase space, and a live AIFS-ENS forecast of relative AAM for the globe and each hemisphere.
- Wave activity flux (Takaya–Nakamura)
What the Takaya–Nakamura wave activity flux shows about Rossby wave packets, downstream development and blocking, the equation, and a live member-averaged AIFS-ENS forecast at 250 hPa.
- 100 hPa eddy heat flux
Why the zonal-mean poleward eddy heat flux at 100 hPa measures planetary waves entering the stratosphere, how its 40-day mean leads the polar vortex, and a live member-by-member AIFS-ENS forecast for both hemispheres.
- Sudden stratospheric warmings and the polar vortex
What a sudden stratospheric warming is, split and displacement events, how SSWs reach the surface, a catalogue of every major SSW since 1980 from MERRA-2, and a live AIFS-ENS polar vortex forecast.
- Hadley cell and the mean meridional mass streamfunction
How the zonal-mean meridional mass streamfunction describes the Hadley, Ferrel and polar cells, how cell strength and edges are measured, and a live AIFS analysis of the overturning against ERA5 1991–2020.
- Dynamic tropopause and potential vorticity (2 PVU)
What the dynamic tropopause is, how to read potential temperature on the 2-PVU surface, isentropic potential vorticity on 330 and 350 K, and live AIFS forecast maps to day 10.