HW 3 - Q1 a. Normally P > 0 in the northern hemisphere. Instabilities result if P < 0. Discuss the two types of instability releases that may occur when P < 0 in a table. Indicate in this table, for each type, the force that destabilizes the air (units m s -2 ) (equation only) the flow direction that results to restore stability the time scale of oscillation (if the atmosphere is stable), expressed as an equation the magnitude of this time scale, using typical values in the troposphere. the typical length scale (distance) of the unstable flow, if instability is present (hint: think about regions where the instability occurs, in the convective BL, in the troposphere, on the equatorward side of the jet … Note that to a first order, the width of the eddies scales with this length scale)

effect of friction on PV curl of friction force

PV banners in lee of complex terrain

example: PV banners in Idaho under NW wind 290 K potential vorticity (filled colors: PVU) 288 K potential vorticity 26 Nov 2005, 18 Z. Source: Andretta and Geerts 20xx

300 mb pvu PVU Note the shear vorticity, suggesting that the PV is generated by friction along orography Some PV is not generated but advected down from UL in downslope wind storm (note slope of isentropes) PV banners in the lee of the Alps

Q1.c If the P anomaly resulting from terrain interaction in the boundary layer (schematic above) is negative, and larger in magnitude than the background P, then what kind of instability (of the two mentioned in (a)) would be released in this case? Explain