lecture 4 weather forecasting. what makes the weather? our earth’s surface consists of land and...
Post on 21-Dec-2015
215 views
TRANSCRIPT
Lecture 4
Weather forecasting
What Makes the Weather?
Our earth’s surface consists of Land and
Water, with Water being thermally stable
substance ( inverse Land ) and weather over
water tends to be more Predictable and stable
than over land.
Equatorial regions receive more solar heat than
Polar Regions
Heat must be transfer to redistributed over
the whole earth’s surface
1
2
On regions 1 and 2 in the previous
figure the winds are not strong
because air motion is vertical, and
horizontal temperature differences on
the surface are slight.
Predicting the Earth’s Complex atmospheric
interactions is a combination of ART and
SCIENCE.
Good analysis and predictions depend upon
a sound grasp of meteorological concepts
weather operates through multiple levels
of TIME and SPACE.
Scale Example Duration
Global ( Rossby waves, 50o-120o longitude)
Jet Stream Weeks to months
Synoptic ( short waves, less than 50o longitude)
Air masses, High- and Low-pressure system
Days / weeks
Mid-latitude and tropical
Surface troughs and ridges, Hurricanes, typhoons, monsoon troughs
week or less
Meso ( intermediate ) Squall lines Several hours / day
Small Thunderstorms, hailstorms A few hours or less
Micro Donwbursts, waterspouts, tornadoes
Less than an hour
Scales of weather development
To analyze and forecast weather
properly, one must begin looking
at the Earth’s atmosphere as a
whole, not only Micro / Meso /
Synoptic, or others.
Upper-level waves are characterized by
undulations in upper atmosphere’s wind flow
with north-south axes,
results from the cold air in northern latitudes
moving south and warm air from southern
latitudes moving north,
and its shape effected by the amount of warm
and cold air with the topography underlying.
On average, there are three to seven Rossby
waves circling the Earth at any given time, in
response to the continuous north-south
movement of warm and cold air within the
Earth’s atmosphere.
Rossby waves have their greatest influnce in
Mid-latitudes, 30o to 60o degrees north and
south.
Embedded within the long Rossby waves a
smaller synoptic scale ( short-wave troughs )
, which extend over large areas and exist a
few days to about a week.
Synoptic-scale waves control the development
and movement of surface high- and low-
pressure systems.