Introduction to G410

transcript

Introduction to G410Daily telemetry observationsGo to www.nwac.us and click on Weather and Snowpack Information.

Go to Alpental and make a table in your notebook that records the following data. Next go to Snoquamlie Pass, record 300’ data only.

Date 5400’ Tmin/max

4300’ Tmin/max

3120’ Tmin/max

RH 5420’

RH 3120’

Wind avg/max

Wind Dir.

Hr prec3120’

Tprec3120’

24 hr snow

Introduction to G410Daily weather and avalanche forecasts

Go to www.nwac.us and click on Forecasts

Read weather and avalanche forecast on a daily basis.

Add notes that help explain your telemetry data

Introduction to G410MOUNTAIN WEATHER FORECAST FOR THE OLYMPICS WASHINGTON CASCADES AND MT HOOD AREANORTHWEST WEATHER AND AVALANCHE CENTER SEATTLE WASHINGTON340 PM PST MON JAN 5 2009...corrected

WEATHER SYNOPSIS FOR MONDAY AND TUESDAYStrong and moist post frontal flow continues Monday afternoon. However the westerly flow is producing widely varying precipitation patterns with the concentration of the heavy precipitation in the north central Cascades, especially Stevens and Snoqualmie Passes where heavy precipitation has been occurring since the warm front passes early Monday morning.

Introduction to G410BACKCOUNTRY AVALANCHE FORECAST FOR THE OLYMPICS WASHINGTON CASCADES AND MT HOOD AREANORTHWEST WEATHER AND AVALANCHE CENTER SEATTLE WASHINGTON915 AM PST MON JAN 5 2009

ZONE AVALANCHE FORECASTSCASCADE PASSES, STEVENS, SNOQUALMIE AND WHITE PASSES-

AVALANCHE WARNING FOR MONDAY THROUGH TUESDAY....

Monday morning: HIGH avalanche danger below 7000 feet. Monday afternoon: HIGH avalanche danger above 4000 feet and CONSIDERABLE below.Monday night: Slowly decreasing HIGH avalanche danger above 4-5000 feet and CONSIDERABLE below.Tuesday and Tuesday night: Significantly increasing danger Tuesday morning becoming EXTREME above 4000 feet and HIGH below.

Introduction to G410

Bring to class1) Textbook – Avalanche handbook2) Calculator3) Pencil and eraser4) Lecture 7:30 pm – 9:30 pm

Bring to field1) Backpack2) Transceiver3) Shovel4) Probe5) Warm clothing -- see list on web site.

Mountain Weather and Energy Flux

Four factors that affect the formation and release of avalanches

Variations in solar heating create our dynamic atmosphere

Reasons Snow Important

•10% of the Earth's surface is covered by glacial ice, with snow covering the glacial ice.

* Small changes in climate can have very large effects on precipitation as snow, the amount of water stored as snow, and the timing and magnitude of snowmelt runoff.

Hydrologic Cycle

10% of the Earth's surface is covered by glacial ice, with snow covering the glacial ice.

Small changes in climate can have very large effects on precipitation as snow, the amount of water stored as snow, and the timing and magnitude of snowmelt runoff.

Phase diagram – H20

The phase diagram is divided into three regions, each of which represents a pure phase.

The line separating any two regions indicates conditions under which these two phases can exist in equilibrium.

Phase diagram – H20 Lets change pressure, and see how the boiling point and freezing (melting), point of water deviate from normal magnitudes.

Here we change the phase of a material without a change in temperature

General Circulation

Unequal heating between equator and pole causes circulation cells

Location of cells correspond to alternating belts of high and low pressure regions.

Cells also correspond to wind.Easterly winds from equator to 30° latitude (trade winds) and 60° to poles.

Westerly winds from 30° to 60°.

Jet Streams

Strong air currents produced by pressure gradient between poles and equator.

Location, strength and orientation vary with season and day to day.

Summer and Winter positions

Jet Streams

Air Masses

Regional scale volume of air with horizontal layers of uniform temperature and humidity.

Form during episodes of high pressure

Location name = origin

M = maritime

C = continental

T = tropical

P = polar

A = Arctic

Air Masses and Fronts

m = maritimec = continentalT = tropicalA = arctic P = polar

Mountain Climates of Western North America

• Four mountain ranges parallel west coast of North America

Coast Ranges Alaska Range Cascades Range Sierra Nevada

• Ranges - perpendicular to the prevailing westerly winds of the mid-latitudes

Coast Range: Elevation varies from N to S. Olympic Mtns are highest portion of Coast Range in the USA

Cascades: Highest peaks are volcanoes. The mean crest elevation is considerably below the elevations of these isolated volcanoes.

North Cascades- somewhat higher elevations and heavy winter snowfalls produce extensive glaciation

Each mountain range varies w/respect to elevation

• Significant barriers to maritime air masses moving into the continent from the Gulf of Alaska and northern Pacific

• Moist air carried inland from the Pacific Ocean is lifted:

• First over the Coast Range• Then over the Cascades

• Low precipitation or rain shadows on the lee side of mountain ranges

West slope of Olympic Mts: 150” (381cm)Sequim, WA = 16 “ (41 cm)

•Supports different ecosystem, semi-arid

shrub/steppe.

Coast Mountains: 2.3 SWE (1-7-2007; Hurricane Ridge, Olympic National Park, Washington)

Cascades Crest: 2.85 SWE (1-7-2007; Alpental Ski Area, Washington)

Eastern Washington: 0.12 SWE (1-7-2007; Mission Ridge Ski Area, Washington)

Winter

• Storms develop in the area of the Aleutian Low & bring near continuous drizzle, rain and moderate coastal winds along the west coast of N. America

• Southwestery winds to the south of low pressure storm systems bring the heaviest precipitation

•Maritime influence moderates the temperatures

Spring

• Pacific High moves northward and intensifies

• Milder, drier weather to the Coast and Cascades Ranges

• Clockwise circulation exposes the coast to winds out of the NW

• High pressure suppresses cloudiness and precipitation

Synoptic (large-scale) weather systems• Monsoons• High & low pressure centers• Fronts

Introduction to the Atmosphere

Composition

A. Three gasesNitrogen (78%)Oxygen (21%)Argon (1%)

B. Other gases• Water vapor (0 - 4% vol)• Carbon dioxide (0.034% vol)

Water vapor and CO2 absorb radiation emitted by the Earth’s surface and reradiate it back towards the Earth

C. Aerosols: natural or man-made• Rain, snow, ice, dust, pollen,• Carbon, Acids

Affect transmission of light - visibilityServes as a nuclei for condensation of

water vapor

D. Humidity• Water content varies

over time and space• Amount of water vapor

depends on air temperature

• Warm air holds more water vapor than cooler air

• High humidity areas are found in warm equatorial regions

Relative humidity

Ratio of actual water content of air to the water vapor content of saturated air at the same temperature

e = actual water vapor pressure

es= water vapor pressure that would have if it were saturated at its current temperature

RH =100e

Relative Humidity• Percentage value• Water vapor content at

saturation rises with T, but actual vapor content does not

• Diurnal variations are present

• Relative humidity reaches max just before sunrise when temp is lowest.

• Relative humidity reaches min in mid-afternoon, when temp is highest.

Latent HeatLatent Heat: the amount of heat energy released or absorbed when a substance changes phases (ice to vapor, or rain to ice)

Introduction Atmospheric Structure

Vertical structure, exponential decrease of air density and pressure with height.

Air pressure: Mass per unit volume of atmosphere

• Millibars or pounds/sq inch

• Air pressure is the measure of weight of a column of air above that level

• Temperature, density, and pressure are closely related.Gas laws exponential decrease of air density and pressure

with height.

P = ρRT P = pressure

= air density

R = gas constant

T = absolute temperature

Atmospheric stability resistance to vertical motion.

• Stable atmosphere = horizontal clouds

• Unstable atmosphere = vertical clouds

In general, clouds form as a result of warm air rising, cooling, and expanding

Unstable atmosphere = vertical motions & vertical clouds

These types of layered clouds are called cumulus clouds

Stable atmosphere = horizontal clouds

These types of layered clouds are called stratus clouds

Air Parcel

• We used the term “parcel” when talking about moving air up or down in the atmosphere– Just a balloon-like volume of air that does not mix

with the surrounding air• New term: Adiabatic - a process in which no heat is

exchanged between an air parcel and the surrounding environment.

– If it rises, the air inside expands and cools– If it sinks, the air inside compresses and warms

Adiabatic Process

• The rate at which a parcel cools as it rises or warms as it sinks depends on whether or not the air is saturated

• Average rate = 6.5º C per 1000 m

• If the air is unsaturated (RH<100%), this rate is 10º C per 1000 m is is called the dry adiabatic lapse rate

Adiabatic change in the atmosphere as a parcel of air rises or sinks.

Moist Adiabatic Lapse Rate• If an unsaturated parcel of air rises and

cools, it will eventually cool to its dew point where it will be saturated (RH=100%)

• Further cooling results in condensation– This is when a cloud begins to form– Also, condensation represents a phase change

of water from a gas to a liquid. Latent heat is released

So if the air still continues to rise, will it still cool at the dry adiabatic rate?

Moist Adiabatic Lapse Rate

No, the rate will be less due to the release of latent heat So, rising saturated air does not cool as

quickly as rising unsaturated air In fact, it cools at an average rate of 6ºC

per 1000 m which is called the moist adiabatic lapse rate

Lapse Rates

RH < 100%

RH = 100%

RH < 100%1000 m

Surface

2000 m

3000 m

Determining Stability

• If a parcel rises and cools, and is then colder than the surrounding air, it will sink back to its original position – stable

• If the parcel is warmer than the surrounding air, it will continue to rise - unstable

Review:Cloud Development and Stability

4 major ways air is forced to rise and produce clouds1) Heating at the surface (convection)

2) Topography (mountains, hills, etc.)

3) Convergence of surface air (air flows come together)

4) Uplift along fronts

Cloud Development and Stability

Convection Hot surface heats air Warm air rises Cooler air from above

sinks to replace it

• If the condensation level is low:

• One thermal may cause a cumulus cloud

• If high:• May take several

thermals

Sinking air at sides causes lots of blue sky in between clouds

Surface Energy Budget

Amount of heat and moisture transferred between the lower atmosphere & Earth’s surface.

Net solar and terrestrial radiation (R) at the Earth’s surface must be transformed into:Latent heat flux (L) used to evaporate or condense waterGround heat flux (G), used to warm or cool the groundSensible heat flux (H), used to warm or cool the atmosphere

Heat Definitions

Latent HeatLatent Heat: the amount of heat energy released or absorbed when a substance changes phases (ice to vapor, or rain to ice)

Sensible HeatSensible Heat: the heat that is transported to a body that has a temperature different than it’s surroundings (the heat difference you can “feel” or “sense”)

Net all-wave radiation term, RAll objects emit radiation.

The wavelength depends on the temperature of the radiating body

The Sun (6,000°C) emits most radiation in the wavelength range of .015-3 micrometers.

Human vision responds to the visible spectrum (0.36-0.75 micrometers).

Terrestrial objects have much lower temperatures and radiate energy at 3-100 micrometer wavelength.

Hot objects emit at short wavelengths

Cold objects emit at long wavelengths

Radiation from the Sun is called shortwave radiation.

Radiation emitted from objects or gases at normal terrestrial temperatures are called longwave radiation.

Longwave Radiation (LWR): heat you can’t see

Shortwave radiation (SWR):

visible light

Net radiation, RBoth short wave and long wave radiation can be directed

upward from the ground or downward from the atmosphere

Four components of the net all-wave radiation term Ra) incoming short wave radiationb) outgoing short wave radiation (fraction of the incoming shortwave

radiation)c) incoming long wave radiation emitted by gases and clouds in the

atmosphered) outgoing long wave radiation emitted by the Earth’s surface and

objects on it.

Diurnal Variations in R

Both solar terms begin at sunrise and end at sunset.

Short wave R peaks at midday

At night, short wave R is zero

Why the lag between svr and T?

Processes affected by energy exchanges

Snow formation in the atmosphere

Snowpack metamorphism Surface hoar formation Near-surface facet formation Temp regimes and gradients

Introduction to G410

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