within this range on which we could expect the normal or  mean  temperature  to  occur.  This  study  could  be broken  down  further  into  hours  of  the  day,  etc.,  as required. REVIEW QUESTIONS Q6-6.    If one adds all the daily high temperatures for the week and divides by 7, what climatological parameter would be determined by this calculation? Q6-7. A temperature of 124 degrees Fahrenheit was the  highest  temperature  ever  recorded  at  a particular station. What type of climatological parameter was determined? Q6-8. What is a degree-day? CLASSIFICATION OF CLIMATE LEARNING OBJECTIVE: Recognize climatic zones and climatic types as they relate to the classification of climate. The   climate   of   a   given   region   or   locality   is determined by a combination of several meteorological elements and not by just one element. For example, two regions may have similar temperature climates but very different precipitation climates. Their climatic difference,  therefore,  becomes  apparent  only  if  more than one climatic factor is considered. Since the climate of a region is composed of all of the  various  climatic  elements,  such  as  dew,  ice,  rain, temperature,   wind   force,   and   wind   direction,   it   is obvious that no two locations can have exactly the same climate. However, it is possible to group similar areas into what is known as a climatic zone. CLIMATIC ZONES The  basic  grouping  of  areas  into  climatic  zones consists  of  classifying  climates  into  five  broad  belts based on astronomical or mathematical factors. Actually they are zones of sunshine or solar climate and include  the  torrid  or  tropical  zone,  the  two  temperate zones,  and  the  two  polar  zones.  The  tropical  zone  is limited on the north by the Tropic of Cancer and on the south by the Tropic of Capricorn, which are located at 23  1/2°  north  and  south  latitude,  respectively.  The Temperate Zone of the Northern Hemisphere is limited on the south by the Tropic of Cancer and on the north by the Arctic Circle located at 66 1/2° north latitude. The Temperate    Zone    of    the    Southern    Hemisphere    is bounded on the north by the Tropic of Capricorn and on the  south  by  the  Antarctic  Circle  located  at  66  1/2° south latitude. The two polar zones are the areas in the Polar  Regions  which  have  the  Arctic  and  Antarctic Circles as their boundaries. Technically, climatic zones are limited by isotherms rather than by parallels of latitude (fig. 6-1). A glance at any chart depicting the isotherms over the surface  of  the  earth  shows  that  the  isotherms  do  not coincide with latitude lines. In fact, at some places the isotherms parallel the longitude lines more closely than they  parallel  the  latitude  lines.  The  astronomical  or light zones therefore differ from the zones of heat. CLIMATIC TYPES Any  classification  of  climate  depends  to  a  large extent on the purpose of the classification. For instance, a   classification   for   the   purpose   of   establishing   air stations where favorable flying conditions are important   would   differ   considerably   from   one   for establishing the limits of areas that are favorable for the growing  of  crops.  There  are  three  classifications  that merit  particular  attention.  They  are  the  classifications of   C.   W.   Thornthwaite,   W.   Köppen,   and   G.   T. Trewartha. Thornthwaite’s  classification  of  climates  places  a great    deal    of    emphasis    on    the    effectiveness    of precipitation.  Effectiveness  of  precipitation  refers  to the relationship between precipitation and evaporation at  a  certain  locality.  Thornthwaite  classified  climates into   eight   main   climatic   groups;   five   groups   give primary  emphasis  to  precipitation  and  the  other  three groups are based on temperature. Köppen’s classification includes five main climatic types.  They  are  tropical  rain,  dry,  warm  temperate rainy,  cool  snow  forest  (boreal),  and  polar  climates. These  main  types  are  further  divided  into  climatic provinces.  The  Köppen  classification  is  based  mainly on  temperature,  precipitation  amount,  and  season  of maximum  precipitation.  Numerical  values  for  these elements constitute the boundaries of the above types, which were selected primarily according to their effect on plant growth. Figure 6-2, shows Köppen’s climatic types. 6-6