quiz 1 Flashcards
wildfires + ch 1
brief description of wildfires
- they are a natural part of the Earth’s ecosystem
- they are a threat to society because they can spread from forests and grasslands to our homes and businesses
- smoke is hazardous
when did fires begin on earth?
- A big part of earth’s history we did not have oxygen, wildfires need oxygen
- Only about 300 million years the earth got up to present day levels of oxygen
what is the source of earth’s oxygen?
by product of photosynthesis
what is fire?
- Rapid oxidation of a material (the fuel) in the exothermic chemical process of combustion, releasing heat, light, and various reaction products.
- At the ignition point, flames are produced.
- The flame is the visible portion of the fire.
- Flames consist primarily of carbon dioxide, water vapor, oxygen, and nitrogen.
fire ingredients (fire triangle)
- Fuel (organic materials) ex: wood, dead materials, etc
- Oxygen
- Heat
- When you put water on a fire you are helping to eliminate oxygen and heat
- Water has a high heat capacity → meaning it takes a lot to heat it
- Knowing history of humidity and type of fuel can help us predict fires
- Weather can affect the severity of a fire → is it raining? How windy is it?
wildfire and climate
- 3 types of climates
wildfires are most common where there are wet and dry seasons in the same region
1. monsoonal climate
2. mediterranean climate
3. grassland
monsoonal climate
- Traditionally a seasonal reversing wind accompanied by corresponding changes in precipitation
- Now it is a seasonal changes in atmospheric circulation and precipitation associated with annual latitudinal oscillation of the Intertropical Convergence Zone (ITCZ) between its limits to the north and south of the equator
→ the ITCZ appears as a band of clouds, usually thunderstorms, that encircle the globe near the equator - most monsoonal zone fires are now intentionally set for agricultural purposes
- About 100,000 monsoonal zone fires a year can be seen from space
mediterranean climates
- comes from the Latin word mediterraneus “midland, surrounded by land, in the midst of an expanse of land”
- Generally areas of very dry summers and wet winters (ex. California)
grasslands
generally along the borders of monsoonal and temperate regions with marginal rainfall
ignition source of wildfires
- two variations
- Natural:
- Lightening → some thunderstorms in mountains have very little rain “dry thunderstorms”
- Spontaneous combustion of rotting vegetation - Human-caused:
- Fallen power lines
- Trains and cars
- Campfires
- Cigarettes
- Arson
fire spread (6)
- Type of fuel
- Moisture content of fuel
- Vertical arrangement of fuel
- WIND
- TEMPERATURE
- RELATIVE HUMIDITY
ground fires
-duff layer
- Burn mostly in decayed roots below ground and in the duff layer
—>Duff layer is made up of compacted dead plant materials such as leaves, bark, needles, and twigs
surface fires
- Burn loose needles, moss, lichen, herbaceous vegetation, shrubs, small trees, and saplings that are at or near the surface of the ground, mostly by flaming combustion
- Surface fires spread in surface fuels dictate much of a fire’s expansion
crown fires
Crown fires burn forest canopy fuels, which include live and dead foliage/branches, lichens in trees, and tall shrubs that lie well above the surface fuels. They are usually ignited by a surface fire.
—> considered most destructive because burns through the tree canopy and hard to stop
anatomy of a fire
- convection
- Convection confines fire but can produce ember or firebrands
- Around the fire hot air rises and creates convection cells
- Air from the sides will replace the air that is going up
→ convection cells constrain the fire
types of heat transfer (3)
- Conduction: heat transfer through direct contact between objects (ex burning your hand on a hot frying pan)
- Radiation: heat transfer through electromagnetic waves
- Convection: heat transfer through the movement of a fluid
Earth emits infrared radiation back to space
→ convection is important in wildfires, next is radiation
wet fuel doesn’t burn easily
Water has a high heat capacity:
- Amount of heat to be supplied to an object to produce a unit change in its temperature
- For wet material, thermal energy will be used to raise temperature of water, stops fuel from getting hot
Water has a high heat of vaporization:
- Takes a lot of energy to evaporate water
- For wet material, thermal energy will be used to evaporate water, stops fuel from getting hot
Vaporized water can starve the fire of oxygen
why it isn’t only rain that matters
- what is a characteristic of wood?
- define relative humidity
- Wood is hygroscopic
—> Hygroscopy: the phenomenon of attracting and holding water molecules via either absorption or adsorption from the surrounding environment, which is usually at normal or room temperature - At high relative humidity, fuels are wet
→ relative humidity: percent of water vapor saturated air
High temperature lowers relative humidity and dries wood
wind role in fires
- supplies more oxygen
- carries firebrands downwind
Santa Ana Winds
- Strong, extremely dry katabatic winds that originate inland and affect coastal Southern California and northern Baja California
- They originate from cool, dry high-pressure air masses in the Great Basin
Katabatic wind
- originates from
- are due to
- Originates from the difference of density of two air masses located above a slope
- This density difference usually comes from temperature and humidity difference (dry air is heavier than wet air)
- Most katabatic winds are due to radiative cooling. This cools the higher air, making more dense
- The slope surface cools down radiatively after sunset, which cools down the air near the slope. This cooler air layer than flows down in the valley
- Everything emits electromagnetic radiation (type of heat). Over high areas with a dry atmosphere the radiation escapes to space.
fire forecasting
- what do you need estimates of
- Complicated but necessary to plan proper use of fire fighting and evacuation planning
- Need estimates of: fuel abundance, fuel water content, lightning probability, winds, and temperature
firefighting
- direct vs indirect
- To let burn or try to control?
- Depends on likelihood of spread and direction
- Direct control:
–>Water
–>Chemical retardants
–>Ground and aircraft deployed - Indirect:
–>Firebreak
aerial firefighting
- Dump water on fires, normally get water from lakes
- Also use chemical retardants
smokejumpers
Often are dispatched to wildfires in remote areas, inaccessible to other firefighters
firebreak
- Make a line where you get rid of the burnable material
- Convection will suck air back into the fire, start a fire on the other side of the break which will burn back into the original fire
- On the other side of the break put chemical retardant
some earth history
The earliest time for the origin of life on Earth is at most 3.5 billion years ago - not long after the oceans formed 4.5 billion years ago and after the formation of the Earth 4.54 billion years ago.
temperature and pressure
- Temperature and pressure are critical properties in meteorology
- Variations in temperature and pressure along the horizontal surfaces and with altitude define the HEAT ENGINE which is the atmosphere
- It is this ENGINE which responds to solar energy input and black-body heat loss which sets up the temperature and pressure gradients that makes the wind blow, moving heat and water through the atmosphere
- It is this ENGINE which evaporates water from the Earth’s surface and cause clouds to forms and precipitation to fall
- It is this ENGINE that causes weather
pressure
Force applied perpendicular to the surface of an object per unit area over which that force is distributed
force
- An influence that can cause an object to change its velocity unless counterbalanced by other forces
- The concept of force makes the everyday notion of pushing or pulling mathematically precise
- Because the magnitude and direction of a force are both important, force is a vector quantity
- In 1687, Newton published, Philosophiae Naturalis Principia Mathematica. In this work Newton set out three laws of motion that have dominated the way forces are described in physics to this day.
atmospheric pressure
- Atmospheric pressure is caused by the weight of the air above the measurement point
- MKS: meters, kilograms, seconds
tangent about the origins of science
- The origins of modern science can be traced to the 6th century BC as can democracy in Miletus, a city of Ionia (in modern-day Turkey)
- Anaximander was an early proponent of science and tried to observe and explain different aspects of the universe, claiming that nature is ruled by laws, which can be deduced from observations of nature.
- Did not rely on supernatural explanations
another foundation of modern science: falsifiability
- Falsifiability: is a deductive standard of evaluation of scientific theories and hypotheses
- A theory or hypothesis is falsifiable if it can be logically contradicted by an empirical test
- Falsifiability is a key notion in the separation of science from non-science and pseudoscience.
temperature
- latitude
- longitude
- Physical quantity that quantitatively expresses the attribute of hotness or coldness. It is a measure of the motion of atoms and molecules.
- Latitude: measure of the number of degrees from the equator to the poles
- Longitude: the distance east and west of the Prime Meridian, which runs through Greenwich, England
temperature scales (3)
- Celsius: the degree celsius is the unit of temperature on the celsius temperature scale (originally known as the centigrade scale outside Sweden)
- Kelvin: is the base unit for temperature in the internal system of units (SI). The kelvin scale is an absolute temperature scale that starts at the lowest possible temperature (absolute zero), taken to be 0 K.
- Fahrenheit: The Fahrenheit scale is a temperature scale based on one proposed in 1724 by the European physicist Daniel Gabriel Fahrenheit (1686-1736). It uses the degree Fahrenheit as the unit.
temperature conversions
Celsius to Kelvin: K=C+273.15
Celsius to fahrenheit: F=(Cx 9/5)+32
layers of earths atmosphere
troposphere
tropopause
stratosphere
troposphere
- nearest the Earth’s surface, with T decreasing as altitude increase
- This is where almost all weather occurs
tropopause
just above the troposphere, with temperatures remaining nearly constant with altitude, possibly increasing slighting
stratosphere
- above the tropopause with temperatures increasing with increasing altitude
- The increase of temperature with altitude is a result of the absorption of the Sun’s ultraviolet (UV) radiation by the ozone layer
temperature and pressure: you should know
1. how temperature varies with altitude
2. major atmospheric layers based on temperature
3. how pressure varies with altitude
- temperature generally decreases with increasing altitude
- troposphere, tropopause, stratosphere
- atmospheric pressure declines as altitude increases
atmosphere is similar to a heat engine
1. what is the source of heat for the atmosphere?
2. how is heat lost from the atmosphere?
3. what is the work done?
- Sun
- radiation to space
- circulation of atmosphere and ocean
what makes the atmosphere an ocean circulate?
Differences in pressures due to changes in temperature and density
why we care about atmospheric moisture
- Source of precipitation
- Major part of atmosphere energy budget
—-> Energy used to evaporate water
—-> Energy released during condensation - Clouds effect radiation balance
—-> Can absorb and reflect radiation - Water is most important greenhouse gas → absorbs infrared that Earth is trying to send back to space
- Moderates temperatures
—-> Water, in particular the ocean can absorb and store a lot of energy, thus moderates coastal temperatures and Earth’s heating
two useful concepts
- heat index: What the temperature feels like to the human body when relative humidity is combined with the air temperature
- windchill: What the air temperature feels like to the human skin due to the combination of cold temperatures and winds blowing on exposed skin
heat index
- When the body gets too hot, it begins to perspire or sweat to cool itself off
- Evaporation is a cooling process
- When the atmospheric moisture content (i.e relative humidity) is high, the rate of evaporation from the body decreases
- If the perspiration is not able to evaporate, the body cannot regulate its temperature
- In other words, the human body feels warmer in humid conditions
windchill
- As wind blows across our bodies it takes the heat we naturally emit and blows it away from our bodies
- The faster the wind speed the faster our body heat is taken away and the colder it feels
Hydrologic Cycle was one of the first scientific explanations of nature
- Anaximander; (c. 610- c. 546 BC) was a pre-Socratic Greek philosopher who lived in Miletus, a city of Ionia (in modern-day Turkey)
- According to available historical documents, he is the first philosopher known to have written down his studies
- Anaximander was an early proponent of science and tried to observe and explain difference aspects of the universe, with a particular interest in its origins, claiming that nature is ruled by laws
- Anaximander’s realization that Earth floats free without falling and does not need to be resting on something has been indicated by many as the first cosmological revolution and the starting point of scientific thinking
science is not static
- Anaximander, who first describes the hydrologic cycle, studied and analyzed the ideas of his teacher but also questioned them. This questioning leads to advances in science.
- All scientific explanations are open to questioning and revision
- Good scientific explanations are just the best explanations at a given time
clouds and climate
- how do clouds affect the radiation budget?
- Reflection of sunlight
- Absorption of emitted radiation
how about water vapor?
- Water vapor is a greenhouse gas
- Greenhouse gasses absorb infrared radiation and act like a thermal blanket warming Earth’s surface
blackbody radiation
- All objects above absolute zero emit radiation (light)
- Earth emits mostly infrared radiation
- Greenhouse gasses absorb or trap infrared radiant energy
phase changes (6)
- Gas to liquid: condensation
- Liquid to vapor: evaporation
- Liquid to solid: freezing
- Solid to liquid: melting
- Solid to gas: sublimation
- Gas to solid: deposition
- Energy is required to change phases
- The energy is needed to break the hydrogen bonds
hydrogen bonds
an electrostatic force of attraction between a hydrogen (H) atom which is covalently bonded to a more electronegative “donor” atom or group (e.g., oxygen), and another electronegative atom bearing a lone pair of electrons. Glue that holds liquid and solid water molecules together
evaporation and condensation
- controlled by?
- rates controlled by?
- Direction (evaporation or condensation) is controlled by water vapor saturation
- Rates are controlled by how far from saturation the air is.
what is “saturation”?
In meteorology, saturation refers to a condition where the air is holding the maximum amount of moisture possible in the form of water vapor. This corresponds to a relative humidity level of 100%
Key Parameters to understanding water vapor saturation
- Air temperature determines the maximum amount of water vapor that air can contain without condensation happening. I.E. saturated air (relative humidity 100%)
- When saturation is exceeded we see dew on surfaces and cloud or fog in air
- The saturation vapor pressure is set the by air or surface temperature
Over what altitude range does most weather occur?
Most weather occurs in the troposphere which is at an average altitude of 6-7.5 miles above sea level
Why does temperature increase with height in the stratosphere?
because of the absorption of ultraviolet (UV) radiation by the ozone layer
What atmospheric variable controls how much moisture the atmosphere can hold?
The higher the temperature, the more water vapor a volume of air can hold, and the higher the saturation vapor pressure
water vapor saturation
- Direction and rate depend on saturation state of air
→ rate of vaporization = rate of condensation - Water vapor pressure vs temp graph is an exponential function
- Undersaturated, supersaturated, saturated
→ saturation is what we need to get rain, fog, snow, etc - As air goes up temperature goes down, air goes up relative humidity increases
What are the main ways air is forced up to form storms
- Cold fronts and warm fronts
- Cold air and warm air collide and warm air is pushed up and becomes saturated
vapor pressure
the pressure of a vapor in contact with its liquid or solid form.
saturation vapor pressure
the pressure exerted by a vapor when it is in equilibrium with its liquid phase at a given temperature
dew point temperature
The temperature that you have to lower or drop to get saturation
relative humidity
The ratio of the actual pressure of water vapor to the saturation (or equilibrium) vapor pressure of water times 100
atmosphere composition
- Water vapor → 0-3%
- Nitrogen (N2) → approximately 80%
- Oxygen (O2) → approximately 20%
- Carbon dioxide (CO2) → approximately 420 ppm
- CH4 (methane) → 1.7 ppm
- CO2 gone from 280 to 420 over the last 200 years → that increase due to human activity especially fossil fuels
Based on the approximately 1.5 C increase in global temperature, about how much has atmospheric water vapor changed over the past 170 years?
Approximately 10% water vapor increase
