not as warm as that moving northward in advance of it. A  warm  core  low  decreases  intensity  with  height  or completely   disappears   and   are   often   replaced   by anticyclones aloft. The heat lows of the southwestern United States, Asia, and Africa are good examples of warm  core  lows.  Newly  formed  waves  are  generally warm core because of the wide-open warm sector. DYNAMIC LOW Systems   that   retain   their   closed   circulations   to appreciable   altitudes   and   are   migratory   are   called dynamic    lows    or    highs.    A    dynamic    low    is    a combination  of  a  warm  surface  low  and  a  cold  upper low  or  trough,  or  a  warm  surface  low  in  combination with a dynamic mechanism aloft for producing a cold upper  low  or  trough.  It  has  an  axis  that  slopes  toward the  coldest  tropospheric  air.  (See  figure  3-22.)  In  the final stage, after occlusion of the surface warm low is complete, the dynamic low becomes a cold low with the axis of the low becoming practically vertical. DYNAMIC HIGH The  dynamic  high  is  a  combination  of  a  surface cold high and an upper-level warm high or well-developed  ridge,  or  a  combination  of  a  surface cold   high   with   a   dynamic    mechanism    aloft   for producing high-level anticyclogenesis. Dynamic highs have  axes  that  slope  toward  the  warmest  tropospheric air. (See fig. 3-22.)   In the final stages of warming the cold  surface  high,  the  dynamic  high  becomes  a  warm high with its axis practically vertical. REVIEW QUESTIONS Q3-11.     What is the term that defines the formation of an  anticyclone  or  the  intensification  of  an existing anticyclone? Q3-12. What is the direction of the windflow around a cyclone? Q3-13. How  do  temperatures  change  within  a  cold core low? Q3-14. Low pressure due to intense heating over the southwestern United States is an example of which type of low-pressure system? TERTIARY CIRCULATION LEARNING  OBJECTIVE:  Define  tertiary circulation and describe how tertiary circulations   affect   local   weather   and   wind direction and speed. Tertiary   (third   order)   circulations   are   localized circulations directly attributable to one of the following causes  or  a  combination  of  them:  local  cooling,  local heating,  adjacent  heating  or  cooling,  and  induction (dynamics). Many   regions   have   local   weather   phenomena caused  by  temperature  differences  between  land  and water surfaces or by local topographical features. These weather  phenomena  show  up  as  circulations.  These tertiary circulations can result in dramatic local weather conditions and wind flows. The most common tertiary circulations are discussed in this lesson. However, there are numerous other circulations and related phenomena in existence around the world. MONSOON WINDS The  term  monsoon  is  of  Arabic  origin  and  means season.  The  monsoon  wind  is  a  seasonal  wind  that blows from continental interiors (or large land areas) to the  ocean  in  the  winter;  they  blow  in  the  opposite direction  during  the  summer.  The  monsoon  wind  is most  pronounced  over  India,  although  there  are  other regions with noticeable monsoon winds. Monsoon winds are a result of unequal heating and cooling  of  land  and  water  surfaces.  During  winter  a massive  area  of  cold  high  pressure  develops  over  the extensive  Asiatic  continent.  This  high  pressure  is  due primarily  to  cold  arctic  air  and  long-term  radiation cooling. To the south, the warm equatorial waters exist and,  in  contrast,  the  area  has  relatively  lower  surface pressures. The combination of high pressure over Asia 3-20 L L H H LEGEND: UPPER AIR SURFACE AG5f0322 Figure 3-22.—Vertical slope of low -pressure systems.