Weather 101 and beyond Edward J. Hopkins Dept. of Atmospheric & Oceanic Sciences Univ. of Wisconsin-Madison Midwest Hot Air Balloon Safety Seminar “Hot Aireventure” Oshkosh 3 March 2001

Concerns of Balloonists The Weather The Terrain (or Surface)

Quiz Ballooning (Fair) Weather is associated with High or Low Pressure? Which way do winds blow around: High pressure? Low pressure?

WIND What is Wind? Why the wind? Review of basic concepts

ASOS Wind Instruments Wind Vane (left) & Cup Anemometer (right)

Aerovane Measures wind speed & direction

BEAUFORT WIND FORCE SCALE [Modern version, Source: Federal Meteorological Handbook I]

BEAUFORT WIND FORCE SCALE (con’t.)

The wind responds to a Difference in air pressure

BASIC CONCEPTS Air Pressure (con’t.)

Explaining Differences in Air Pressure Low Pressure High Pressure

Display of Pressure Differences on a Weather Map - Isobars

Isobars - - lines of equal barometric pressure - use sea level corrected pressure

AIR PRESSURE in the Vertical (con’t.)

As a Sidebar… Altimetry Since pressure decreases at a “reasonably” known rate of 1 mb decrease per 10 meter rise or 0.01 inch of Hg per 10 feet, then… pressure altimeters are barometers made to read in altitude. But...

Pressure Change with height depends upon Temperature of column - (It is really the density!)

WHY THE WIND? (con’t.) Reasons for Atmospheric Motions: Buoyancy Effects or Dynamic Effects

Daily Heating Heat Gain Heat Loss Daylight Nighttime

January Temperatures - Madison, WI (1981-90) Nighttime Daylight Nighttime

January Wind Speeds - Madison, WI (1981-90) Nighttime Daylight Nighttime

July Temperatures - Madison, WI (1981-90) Daylight Nighttime Nighttime

July Wind Speeds - Madison, WI (1981-90) Daylight Nighttime Nighttime

ENERGY TRANSPORT: CONVECTION

LAPSE CONDITIONS Temperature decreases with height

ISOTHERMAL CONDITIONS Temperature remains constant with height

INVERSION CONDITIONS Temperature increases with height

U.S. STANDARD ATMOSPHERE See Fig. 1.9 Moran & Morgan (1997) Thermosphere Mesopause Mesosphere Stratopause Stratosphere Tropopause Troposphere

WHY THE WIND? (con’t.) Reasons for Atmospheric Motions: Buoyancy Effects or Dynamic Effects

Air Converging Aloft

Air Diverging Aloft

The Surface The “Obvious” The Surface and the Winds Obstacles to take-off and landing (e.g., trees, power lines, animals) The Surface and the Winds Affects the Boundary Layer wind flow Can produce local wind regimes

Boundary Layer Where we live Extends from surface to approximately 3000 ft. (1000 m) Consists of Surface Boundary Layer (30 to 60 ft. & includes Anemometer Level) Ekman or Spiral Layer (above 60 ft. to Free Atmosphere)

Relative Surface Roughness Source: Stull, 1995

B. EXPLANATIONS of ATMOSPHERIC MOTION Practical Problems Historical Concepts Forces of Motion & Newton's Laws

An example of an equation of motion NASA

PRESSURE GRADIENT FORCE

PRESSURE GRADIENT FORCE (con’t.)

ASSUMPTIONS For convenience, assume that: Winds are nearly horizontal; Atmosphere is in nearly “hydrostatic balance” i.e., air parcels do not accelerate upward or downward;

HYDROSTATIC BALANCE CONCEPT See Fig. 9.11 Moran & Morgan (1997)

HORIZONTAL PRESSURE GRADIENT FORCE (con’t HORIZONTAL PRESSURE GRADIENT FORCE (con’t.) Direction is from High to Low pressure!

HORIZONTAL PRESSURE GRADIENT FORCE (con’t. ) See Fig. 9 HORIZONTAL PRESSURE GRADIENT FORCE (con’t.) See Fig. 9.1 Moran & Morgan (1997) Magnitude depends on isobar spacing!

LOCAL WINDS FLOW RESPONDING TO PRESSURE GRADIENT FORCE - LOCAL WINDS Assumptions: Only Pressure gradient force operates; Results from temperature differences Acts for short time & short distances. Examples: Sea-Land Breeze Circulation Mountain-Valley Breeze Circulation City-Country Circulation

Sea (Lake) Breeze (Graphics from UIUC WW2010)

VERTICAL PRESSURE GRADIENTS - Dependency on density (temperature)

Sea (Lake) Breeze (con’t.)

Sea (Lake) Breeze (con’t.)

Sea (Lake) Breeze (con’t.)

Sea (Lake) Breeze (con’t.)

Sea (Lake) Breeze (con’t.)

Sea (Lake) Breeze (con’t.)

Sea (Lake) Breeze (con’t.) See Fig. 12.2 A Moran & Morgan (1997)

Land Breeze

Land Breeze (con’t.)

Land Breeze (con’t.)

Land Breeze (con’t.) See Fig. 12.2 B Moran & Morgan (1997)

Mountain Breeze See Fig. 12.14 Moran & Morgan (1997)

Valley Breeze See Fig. 12.14 Moran & Morgan (1997)

Larger Scale Flow Observation:

Right with Height

PRESSURE GRADIENT FORCE

Reason for the Problem Because the earth turns:

CORIOLIS EFFECT or FORCE (con’t.)

Geostrophic Adjustment

Geostrophic Wind See Fig. 9.12 Moran & Morgan (1997)

Flow in Friction Layer

Variation of Friction Effects with Height

Right with Height

Varying effects of Surface Roughness

Curved Flow

Features in a Surface Low (Convergence & Ascent)

Features in a Surface High (Sinking & Divergence)

Numerical Weather Prediction

Numerical Weather Prediction

Numerical Weather Prediction

My office: Dept. of Atmospheric & Oceanic Sciences hopkins@meteor.wisc.edu

UNSTABLE CONDITIONS Compare Environment with DALR Warmer parcel continues upward