1.6 – Atmospheric variations exist on a large range of scales:br /ulliplanetary: features on the scales of continents and oceans/lilisynoptic: variations on a scale that is resolved by a traditional, station based, observation system – roughly features on 100-1000 kilometers/lilimeso: waves, eddies and jets with scales 10s-100s of kilometers, fronts, squall systemsbr //lilismall: anything smaller – individual storms and smaller/li/ul1.6.1 – When longitudinally averaged around the globe, the zonal (east-west) winds are typically an order of magnitude stronger than the meridional (north-south) winds. In both hemispheres, there are jets in the mid-latitudes at around 10km, approximately at the tropopause “discontinuity” between tropics and extra-tropics.br /br /1.6.2 – Tropospheric winds at middle and high latitudes.br /Tend to blow parallel to the isobars, with low pressure on the left in the NH – geostrophic balance.br /Around 500mb, the climatological isobars are slope upwards towards the poles, leading to a prevailing westerly throughout the middle and high latitudes. Near the surface, the circulation becomes more complicated, with a number of closed loops.br /br /1.6.3 – Tropospheric winds at low latitudes.br /Tropical winds generally blow more steadily from day to day. Over the Atlantic and Pacific, the flow is dominated by the Easterly on the equatorial flank of the subtropical highs at ~30^o.br /br /Superposed upon the planetary scale flows is a spectrum of synoptic scale waves which cause nourth/south fluctuations in the direction of this wind – Easterly Waves. Also tropical cyclones – intense circular vortices.br /br /Within the lowest km, the winds are steady and directed partly equatorwards, meeting in a norrow belt called the ITCZ (Inter-Tropical Convergence Zone), usually located a few degrees north of the equator, characterized by strong upwards motion and heavy rainfall.br /br /There is also a strong seasonal dependence – Monsoon.