Download Synoptic Map

Weather Systems, Hurricanes,
etc…
Nili Harnik
DEES, Lamont-Doherty Earth Observatory
[email protected]
Coriolis Force
The Coriolis Force On Earth
Coriolis force
Cloud types, as a function of height
Tropical cyclones (or hurricanes or
typhoons)
Tropical cyclone, also called hurricane and typhoon, is the names
given to an intense low pressure region that forms and migrates in
the tropical ocean regions and is associated with intense winds and
a very strong convection activity which brings thunderstorms and
large amounts of rainfall
Tropical cyclones (or hurricanes or
typhoons)
Hurricane Vertical Cross Section
•The massive disturbances that
sometimes grow in a time frame of
a week or so, need specific and
favorable conditions to occur, such
as high sea surface temperatures
(at lease 26°C) and weak vertical
wind shears. Once they do, they
spreads over a radius of a few
hundred kilometers.
•Hurricanes are surrounded by
rings of towering thunder clouds
spiraling up to a small circle at the
center of the storm, with a radius of
30-40 km. Here the winds can
reach a speed of 100 km/hour and
more and the most intense rainfall
occurs. Inside this ring lies the eye
of the storm, where the air is still
and the convection is suppressed
by slow downward motion
(subsidence).
Regions of Hurricane Activity
•Hurricanes are active in the "trade
wind" belts - the regions just north
or south of the equator where the
winds blow quite steadily from east
to west (easterlies).
•Here tropical disturbances
generally form, initiated by weak
pressure perturbations that exist all
the time in the tropics. They move
west with the trade winds in a
steady, relatively slow motion (1020 km/hour). During this phase they
intensify mainly through the release
of latent heat in the surrounding
clouds and a small percentage
reach full hurricane intensity.
•Hurricanes tracks curve eastward
and they speed up north of ~30°N
Hurricane watch
• http://www.hwn.org/
• Satellite loop:
http://www.hwn.org/atlantic/ir-loop.htm
• http://hurricane.terrapin.com/
Mid Latitudes
The rule of the Coriolis force….
Geostrophic balance
Geostrophic Balance: f u = - (∆ p / ∆ y) / ρ
Pressure Gradient Force (PGF) = Coriolis Force (CF)
Geostrophic flow and friction
This means that a new balance is achieved in which friction and
Coriolis forces together counter the pressure gradient force.
Geostrophic flow and friction
That is why low pressure systems generally bring
stormy weather, while high pressure systems bring
sun.
Isobars
strong gradient
strong gradient
weak gradient
Midlatitude weather systems /Fronts.
In the middle latitudes the flow is broken into sequences of low and
high pressure cells moving from west to east. As we discussed
above, these lows and highs affect the local vertical motion
through convergence and divergence induced by surface friction.
They also sweep air masses of different temperature from north
and south bringing alternations in temperature to the regions they
pass by in their eastward procession. The moving air masses
collide and at their boundaries fronts are created in the low
pressure centers.
A passage of a front indicates an imminent change of temperature
and also a change in weather. There are two kinds of fronts:
Warm fronts and cold fronts.
Synoptic Map
•This segment taken from a
synoptic (weather) map of
surface pressure shows
isobars (contours of equal
pressure in mb) and small
flags, depicting the wind
direction (the flags fly in the
direction of the wind) and
speed (each full flag bar is 10
knots and half a bar is 5 knots
with 1 knot = 1/2 m/s).
•The flow is very close to
geostrophic balance
everywhere with a small
tendency to flow across
isobars towards the low
pressure center - a result of
the friction effect close to the
surface.
Midlatitude weather systems /Fronts.
Warm fronts and cold fronts.
Midlatitude Weather Systems
Midlatitude weather systems
/Fronts.
•
Cold fronts.
Life Cycle of Midlatitude Cyclones
Dynamic Meteorology
The Coriolis Force / geostrophic flow