The Generation of Global Rotational Flow by Steady Idealized Tropical Divergence

Asymmetry of the winter extra-tropical teleconnections in the Northern Hemisphere associated with two types of ENSO

“…In the same way, a CP El Niño (La Niña) case is defined when the normalized EMI is greater (less) than 0.8 (−0.8) and also greater than Niño3 index. Thus, six CP El Niño (1968, 1977, 1994, 2002) and seven CP La Niña (1973, 1983, 1988, 1998, 1999 cases are chosen through this approach.…”

“…To answer this question, the Rossby wave source (RWS) is diagnosed according to Sardeshmukh and Hoskins (1988), which represents the generatioin of vorticity forcing. It is calculated from the barotropic vorticity equation at 200 hPa and the equation is as follows:…”

Large‐scale context for the UK floods in summer 2007

“…Therefore, it is possible for such a wave pattern to exist in the absence of any forcing (a free mode). However, stationary Rossby waves can be generated by a number of processes: by large-scale divergence in the upper troposphere associated with condensation and latent heating (Sardeshmukh and Hoskins, 1988) and by mountains and temperature contrasts along the ground (e.g., land/sea contrasts) (Hoskins and Karoly, 1981). If a wave source switches on, the stationary wave pattern will grow, with wave energy radiating away from the source at the group velocity.…”

Slow oceanic teleconnections linking the Antarctic Circumpolar Wave with the tropical El Niño‐Southern Oscillation

“…This anomalous divergence must be balanced by anomalous convergences and subsidence elsewhere in the upper troposphere, and this has often been thought to occur uniformly over the western and central Pacific. However, observational evidence now shows that this compensation tends to be localized [Sardeshmukh and Hoskins, 1988] and can be described in terms of a regional Hadley cell with anomalous meridional circulations [Rasmusson, 1991]; these provide extraequatorial vorticity sources for the forcing of tropospheric planetary waves that communicate ENSO signals to higher latitudes. In the South Pacific the poleward limb of the seasonally dependent regional Hadley cell is centered over an area north of New Zealand [Rasmusson, 1991].…”