Fog!                                                            4/6

     1.  Please explain question #35 on the last exam which dealt with the location and fragment direction of
         breaking windows in a severe windstorm.
                  Bernoulli's principle tells us that, other things being equal, the lowest pressures in a moving fluid occur where the
                 fluid speed is highest.  Hence a blowing wind will create the lowest pressures on the sides of the building which align
                 with the wind direction with higher pressures occurring on the building sides facing into or away from the wind where
                 eddies will occur and speeds will be lower.  Thus a west wind will create the lowest pressures on the north and south
                 faces of a building and that's where the windows will break, outward because the pressure will be greater in the still
                 air inside the building.

     2.  In a general sense what happens in low and high pressure areas?
                     At the surface, low pressure causes convergence.  The effects of this convergence depend upon the scale of the
                 phenomenon.  On a global scale the monsoonal flows which converge on continental regions in the summer and the
                 convergence of the trade winds towards the equator are a consequence of low pressure and ensuing convergence.
                 At the synoptic scale both middle latitude cyclones and tropical cyclones are regions of convergence wherein the
                 converging air rises, cools, and the water vapor therein condenses to form clouds and possibly precipitation.  On a
                 mesoscale, small regions of low pressure are associated with the circulation in a forming thunderstorm, the influx of
                 air towards a tornado funnel and the gentle circulation patterns of the sea breeze and mountain and valley breezes.
                 At the microscale, eddies such a dust devils and other small eddies such as are experienced in the vicinity of buildings
                 on a windy day, are a result of microscale pressure gradients associated with pressure variations.  The low pressure
                 regions which are identified by an "L" on a weather map are synoptic-scale features.  The cloud mass and
                 precipitation intensity (if there is any) associated with such a feature depend on factors such as the strength of the low,
                 the moisture content of the air in which it forms and the vertical structure in the temperature profile.
                    High pressure at the surface is associated with divergence and subsidence.   Such regions usually have minimal
                 clouds aloft, but at the surface haze and fog may occur if conditions are right.  As with low pressure regions, the effects
                 of highs depend upon scale.  Global scale high pressure is associated with the winter offshore winds of certain
                 continental monsoons, polar easterlies and the tracks followed by tropical cyclones as they are steered around
                 subtropical highs.  Circulation about subtropical highs drives the oceanic gyres.  On a synoptic scale (the scale of the
                 weather map "H"), highs are associated with (usually) clear, sunny skies.  On the mesoscale and microscale, the
                 pressure gradients which arise from the interaction between highs and lows are responsible for the wide variety of
                 circulation patterns which occur as mentioned in the preceding paragraph.
                    Lows and highs aloft are usually unclosed structures called troughs and ridges rather than closed features as they
                 often are at the surface.  Because of the Coriolis force, in the absence of appreciable friction, the flow patterns aloft
                 seldom converge directly on troughs or diverge directly from ridges, rather, subtle patterns of divergence and
                 convergence develop in the winds aloft, often triggering the formation or degradation of surface lows and highs
                 below.

     3.  Could you explain the temperature and wind patterns of the different levels in the atmosphere.
                    The atmospheric layers with which we have dealt in this course, the troposphere, the stratosphere, the mesosphere
                 and the thermosphere are defined by the reversals in the vertical temperature gradient. The troposphere normally has
                 a decreasing temperature as altitude increases, the stratosphere has an inverted gradient where the temperature
                 which increases with altitude.  The sense of the gradient in the mesosphere is the same as in the troposphere and
                 another gradient reversal produces an inversion in the thermosphere.  Winds in the troposphere are mixed and
                 variable, but usually increase with altitude, reaching maximum values in the tropopause.  Above that, winds are
                 minimal all the way through the thermosphere.