The weather and climate of planet Earth is driven by energy exchanges.

      The prime driver is energy (solar radiation) coming from the sun.  This varies with time of year (creating the cycle of the seasons), time of day (giving the day/night cycle), and latitude (the seasonal cycle is small at the equator, and increases towards the poles)

    Ch.2:

     especially 44-50

                     53-59

Spring  in the NC Mountains

Because of our latitude and location we experience marked seasonal changes in incoming solar radiation.  There is a great amount in summer, but much less - albeit still plenty compared to many other places on earth - in the winter.

     Much of this solar radiation is absorbed by the earth's surface where it causes heating. (The proportion of incoming energy absorbed is determined by the albedo of the surface - snow has a high albedo, water has a low one).

     In mid-latitudes, there is a major seasonal cycle, resulting in contrasts between land and water - the continentality effect.  Continental interiors heat fast and to high temperatures in spring/summer, oceanic areas are much slower to heat and do not get too hot.  In winter continental interiors are cold, oceans are cool.

    Ch.4, 

    especially 93-99

Snow on the mountains

    The energy absorbed by the surface must eventually be sent back to space, otherwise there would be rapid climate changes.  Ultimately, only longwave, terrestrial radiation can be emitted to space.  This radiation is first emitted by the surface of the earth. Some goes straight out to space, some is absorbed by the greenhouse gases, which then re-radiate the terrestrial radiation both back to earth (where the emission and absorption cycle starts again) or out to space.

     The greenhouse effect occurs because greenhouse gases allow incoming solar radiation to pass virtually without absorption, but absorb the outgoing terrestrial radiation.  This is a natural effect, but human actions are increasing the concentration of some gases and the effect is increasing.  This, it is believed, is likely to lead to an overall warming of the planet.

    Ch.4: 

       especially 100-108

    Ch.10: 

       especially 289-295

The greenhouse effect in not the only climatic 'problem'.  The death of trees on the highest mountain peaks has also been connected with human impacts on the atmosphere

      The greenhouse effect is connected with global warming, but we do not yet have any clear idea how this will translate into changes on a continental - let alone a state - scale.

     We do know that over the last few decades North Carolina, along with the southeast in general, has cooled very slightly.

     Not all the absorbed solar energy is sent from the surface as terrestrial radiation.  Some heats the ground (in summer) or comes from the ground to the surface (in winter).  Some flows into the air directly as sensible heat (heat you can feel).  Some evaporates water, leading to cloud & precipitation.  All together they constitute the energy budget, and the balance between them determines temperatures

   Ch.4:

   especially 92-98, 

                  103-106

A layered look to the atmosphere of the Piedmont, created by the decrease in the sensible and latent heat flow into the atmosphere as the day draws to a close. 

     The various energy flows have an influence not only on the temperatures, but also on the mode of cloud formation, on the amount of haze (or pollution) in the air.  

    The Sandhills region of the state, being very well drained, has rather little latent heat flow (evaporation), and as a result the energy balance acts to warm the area rapidly in the spring - giving ideal peach growing condiitons.

    All cities are also 'dry' like the Sandhills. Although we have relatively little information about conditions in our major cities, it has been shown that downtown Chapel Hill is warmer than the suburbs.

  Actual temperatures at any point  depend on the energy balance at that point at that time.  This gives an infinite variety of temperatures.  However, we can generalize the results to say that temperature is determined largely by:

(a) latitude; (b) continentality; (c) altitude; (d) local factors.

   Ch. 5, 

   especially 120-121

                   122-127

                   128-137

A weather observing station in the mountains

Our global position (latitude and the location on the east side of a continent, with wind blowing over us off that continent much of the time) dictates that we have warm to hot summers and cool winters.

   The south coast tends to be warmest, the northern mountains the coolest.

   However, there are many local effects. Valley bottoms, for example, are frequently cooler than the valley sides - or in some cases even the valley tops - because cold air tends to drain downwards.

Some of the evaporated water vapor will form clouds - much will simply contribute to humid conditions  For clouds, the air must become saturated, usually by cooling the air.  This commonly involves vertical motions: (a) orographic; (b) convergence (including frontal uplift); or (c) convective.  The cloud types we see depend on the process for this lifting. 

      In many cases the type and intensity of the precipitation created also depends on the type of uplift.  

  Ch.7: 

  especially 187-191 

                  197-199

Evening mist on a western lake

      For North Carolina as  whole, it is possible to say in general terms that during the winter virtually all of the precipitation we get comes as the result of convergence associated with the passage for storm systems. Most of that precipitation is rain, these is a snow 'gradient', with some in virtually every winter in the mountains, the possibility each year in the Piedmont, with snow on the Coastal Plain being a rather rare event.  In summer we also get this widespread, steady and long-lived convergence rainfall, but on average we get about an equal amount of localized, intense showery rain from convective (thunder-)storms.  However, amounts from summer to summer are much more variable than in winter.

     Nevertheless, we do have, on average a fairly even distribution of precipitation through the year, with about 40" on the Piedmont, rather more (say 50") on the Coastal Plain, and commonly much more (about 60") in the mountains.  The mountains are the area for the orographic effect - very wet in places, very dry in others.

    Ch.6

    especially: 150-155

                    155-165

A stormy, windy day near the coast with a Nor'easter in the area

    North Carolina is dominated by winds having a westerly component.  Much of the state, however, has rather low average wind speeds - although they are higher in winter than in summer.  The mountain peaks are exceptions - wind commonly increases with altitude.  So are the coasts - there is less friction to slow the wind over the oceans.

    Sometimes, especially in summer, we may have days of virtually calm conditions, when a high pressure area (the Bermuda High) sits overhead.  During these times sea breezes near the coast can be very apparent.

    At other times, with some storms, and especially with hurricanes, wind speeds may be very high.

    As a result of the global pressure distribution, the mid-latitudes are the area of the "Westerlies" - a belt of air moving generally from west to east.  This can be compared to a river - a somewhat meandering main line of relatively fast-moving airflow, with adjacent calmer areas to north and south.  Positions vary somewhat randomly, and in a more predictable fashion, with the seasons.

      The calmer regions are the source regions for 'air masses', while the main flow represents the areas dominated by the jet streams at high level, while the wave cyclones (frontal depressions) occur over a deeper layer and extend down to the surface.

  Ch 8, 

  especially 211-214; 

                  221-227 

                  233-241

  Our day-to-day weather is a mixture of air masses and storms.  In summer the mT - hot, humid, often cloudy, hazy - air mass dominates, while in winter it alternates with the cP - cold, dry, cloudless, clear - air mass

    Depressions, bringing changing conditions, but usually involving clouds and rain, come at any time in the year.  In winter they tend to give more widespread cloud and prolonged rain than in summer, where frontal uplift is most likely to create our precipitation.