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ERTH 1030 Notes: Chapter 3

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School
Dalhousie University
Department
Earth Sciences
Course
ERTH 1030
Professor
Dr.Anne- Marie Ryan
Semester
Winter

Description
Geography  1030  Notes       Chapter  4:  Humidity  and  the  Water  Circulation  Patterns       Water  and  the  Hydrosphere     the  hydrosphere  counts  as-­‐oceans,     ice  sheets  +  glaciers-­‐the  fresh  part  of  water  freezes   surface  water-­‐wetlands,  rivers,  lakes,  etc.       The  Hydrologic  Cycle   Water  moves  among  the  ocean,  atmosphere,  and  land   -­‐evaporation   -­‐precipitation   -­‐transpiration:  evaporation  off  plants     -­‐evapotransportation     -­‐run  off     -­‐sinks  into  soil   -­‐recharge  of  groundwater  (refill)-­‐rain,  snow     World  Patterns  of  Air  Temperature   Three  main  things  effect  air  temperature  patterns  around  the  globe;  latitude,  maritime-­‐continental   contrast,  and  elevation   Isotherm:  a  line  on  a  map  drawn  through  all  points  with  equal  temperatures     Temperature  gradient:  the  rate  of  temperature  change  along  a  selected  line  or  direction         The  Temperature  Record  and  Global  Warming   Several  methods  can  be  used  to  find  out  climate  from  olden  times:   -­‐tree  rings   -­‐glacier  cores  (ice  core  in  general)   -­‐ancient  sediment     -­‐coral  reef  coring     the  crystalline  structure  of  ice,  concentrations  of  salt  and  acids,  pollen,  amounts  of  each  trapped   atmospheric  gases  all  reveal  information  pertaining  to  long  term  climate  change  patterns       some  past  climate  variation  is  due  in  part  to  volcanic  eruptions     Humidity     Amount  of  water  vapour  (humidity)  in  the  air     Maximum  humidity  if  a  mass  of  air  increases  sharply  with  rising  temperature     Air  at  room  temperature  (20degrees)  holds  3x  the  water  vapour  as  freezing  air  (0  degrees)   Low  humidity  and  heat▯  desert       High  humidity  and  heat  ▯  very  vegetative  (tropics)   100%  humidity=  rain,  fog,  mist.       Relative  Humidity  (RH)   Compares  the  amount  of  water  vapour  present  to  the  maximum  amount  that  can  hold  at  that   temperature     Expressed  as  a  percentage     Air  holding  half  its  capacity  has  an  RH  of  50%       Can  change  in  two  ways:   Air  gains  or  loses  moisture     Air  changes  temperature▯  drop  results  in  rainy  weather     Specific  humidity:  maximum  amount  of  air  can  hold  a  t  a  given  temperature  (highest  in  central  latitudes,   measured  in  g/kg)   -­‐most  often  found  in  higher  temperature  areas,  but  not  always     Dew  Point   The  temperature  at  which  air  at  a  given  humidity  will  reach  saturation  web  cooled  without  changing  its   pressure   Dew-­‐drop  in  temp  with  enough  moisture  condensed  out  onto  the  ground   Frost-­‐drop  in  temp  (below  zero)  moisture  condenses  and  freezes  on  ground     What  happens  as  air  is  cooled  below  the  dew  point  temperature  at  temperature s  above  freezing?  Frost.     Variables  in  Relation  to  Humidity     Temperature   Pressure     Adiabatic  Processes   as  a  parcel  of  air  rises,  atmospheric  pressure  drops,  the  parcel  expands  and  cools   No  horizontal  movement  occurs.   No  wind.  Not  much  anyway     As  air  cools  to  the  dew  point,  clouds  form  (dew  point~  condensation)   Adiabatic  processes-­‐processes  in  which  the  temperature  of  a  parcel  if  air  changes  in  response  to  a   change  in  atmospheric  pressure  only   -­‐that  is,  just  by  rising  and  falling       the  Dry  Adiabatic  Rate  (lapse  rate):   the  rate  at  which  rising  air  cools  or  descending  air  warms  when  no  condensation  is  occurring  (fig.  3.10)   dry  lapse  rate  is  10°C/  1000m   air  is  dry,  not  saturated     The  Moist  Adiabatic  Rate   The  rate  at  which  rising  air  is  cooled  by  expansion  when  c ondensation  is  occurring:  ranging  from  4-­‐9°C   per  1000m     Water  takes  longer  to  cool  than  air   The  moist  adiabatic  lapse  rate  is  less  for  moist  air       Clouds  and  Fog   Clouds  consist  of  water  droplets,  ice  crystals,  or  both   Fog-­‐low  lying  clouds     Condensation  nucleus-­‐a  tiny  bit  of  solid  matter  (aerosols)  is  the  atmosphere,  on  which  water  vapour   condenses  to  form  a  tiny  water  droplet     Clouds
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