ATS/ESS 452: Synoptic MeteorologyFriday 08 January 2016

• Review Material• Overview of Maps

• Equations of Motion• Advection• Continuity

What is Synoptic Meteorology?

Definition: Synoptic meteorology is the study of the structure and evolution of weather systems on spatial scales of order 1000+ km

Synoptic means “view together” or “view at a common point.”

In this course, you’ll learn to view different parameters of the atmosphere together in order to examine/analyze the weather.

What do YOU expect to get out of this course?

This course will help you to begin thinking like a meteorologist.

BUT…this is not a weather forecasting course…instead you’ll begin to learn how the weather “works.”

Quick Map Introduction & What’s Down the Road

What is this?

What type of map is this? What important information is shown?

Notice how the winds flow with respect to the isoheights.

What happened here?

Heavy rain is forecasted for the TN Valley

Relate the location of the upper-level low and it’s associated vorticity to our forecast.

Much more goes into making a local forecast, but what’s happening at 500 mb can tell you a lot and is very important on the synoptic scale!

Corresponding 60-hour 300mb forecast chart. What does this chart show?

The information on this chart (jet level dynamics) will later be important for the ageostrophic wind equation. In general, lift/vertical motion is enhanced in the right-rear and left-front quadrants of jets

Notice in this case, the upper-level low is vertically stacked. This isn’t always the case, and in fact, is not good for a developing cyclone. Want to see a westward tilt with height for a developing cyclone – more on this later

Later forecast… the previous shortwave that was affecting us is forecasted to move into New England

Highly amplified trough pattern has developed over the mid-US

Check out the air pouring out of Canada POLAR air mass

What do would you expect after the trough passes the TN Valley?

Now… notice how there is a westward tilt with height of the cyclone

Also, very strong cold air advection.

Scales of MotionScale Approximate

Length ScaleApproximate Time

ScaleTypes of Phenomena

Planetary > ~ 6000 km > 1 week

Synoptic Scale

1000 – 6000 km 1 day – 1 week

Mesoscale 1 – 1000 km 1 hour – 1 day

Microscale < 1 km < 1 hour

This information is important for simplifying the equations that describe our atmosphere through a process known as scale analysis

**Determine which physical processes are most important and which can you neglect.

Jet Stream, Trade Winds, Longwave pattern

Shortwaves, Fronts, Jet Streaks

Thunderstorms, Sea Breezes

Turbulence, Boundary Layer Phenomena

Variables, Coordinates, & Units• Cartesian coordinate system (x, y, z) is the most typical coordinate system used in

meteorology- x: zonal (East-West) direction; positive towards the east- y: meridional (North-South) direction; positive to the north- z: vertical (up-dpwn) direction; positive upward

• What other coordinate system do you think we will use?- Pressure coordinates

Quantity Unit SI units and notationLength Meter M

Time Second S

Mass Kilogram Kg

Temperature Kelvin K

Velocity Meter/Second m s-1

Force Newton N (kg m s-2)

Pressure (force/area) Pascal Pa (N m-2 or kg m-1 s-2)

Energy or work Joule J (N m or kg m2 s-2)

Variables, Coordinates, & UnitsWind velocity are based on the time rate of change in the distance along its respective coordinate axes following the airflow

zonal wind:

meridional wind:

vertical wind:**start to refer to directions using these names

The Coriolis parameter (f) is related to the spin of the Earth and is given by:

where φ is the latitude and Ω is the rate of Earth’s rotation (7.292 x 10-5 rad s-1)

Synoptic Scale Governing EquationsFrames of reference:

• Eulerian – object is fixed in space; it doesn’t move; changes due to air moving through the object; Referred to as the local derivative in equations

• Lagrangian – object is allowed to move with the air; Referred to as the total derivative in equations

• What is cold air advection (CAA)? What is warm air advection (WAA)?

• Cold air advection is the process in which the wind blows from a region of cold air to a region of warmer air

• Warm air advection is the process in which the wind blows from a region of warm air to a region of cooler air

CAA WAA

Temperature Advection

Temperature Advection

Where’s the Temp Advection?

Where’s the Temp Advection?

Geostrophic Wind**A scale analysis of the *horizontal* governing equations reveals that only the pressure gradient force and Coriolis are important on the synoptic scale

The resulting balance between these terms is called geostrophic balance, which yields the geostrophic wind

**At the synoptic scale, in the Northern hemisphere, the geostrophic wind blows parallel to isobars (isoheights) with low pressure (low heights) to the left.

Geostrophic balance allows the governing equations to be simplified considerably and allows the development of quasi-geostrophic theory (chapter 2)

Notice how wind in this 500mb map is flowing west to east, generally paralleling the isoheights geostrophic balance

Geostrophic balance does not always apply surface

Vertical Momentum Equation

Which terms are left if you perform a scale analysis on this equation?

All that remain are the vertical PGF and gravity.

The balance between these two terms is called hydrostatic balance.

**Synoptic scale motions are largely in hydrostatic balance in the vertical direction

If we are to assume hydrostatic balance, then are we assuming no vertical air motion (i.e. no vertical acceleration)?NO… they’re just very small compared to the vertical PGF and gravity

Vertical acceleration

Vertical PGF Coriolis gravity friction

Continuity Equation• This relation is based on the conservation of mass (in a closed system, mass will not

change).

• The kinematic method uses the continuity equation to estimate vertical motion- Not very accurate- Errors in actual wind observations will lead to very large errors in the vertical

motion estimate

• Convergence of winds at the surface leads to vertical motion

• What do you think convergence aloft leads to? Divergence of winds aloft?(sinking air)(rising air)

• Being able to correctly diagnose and forecast divergence and convergence aloft is an important component of this course

Most 700mb charts show negative values of “omega”…. Realize the differences between w and ω