Weather and Climate exam #1 (Chapter 3)
Albedo refers to the fraction of radiation reflected by an object An increase in the albedo reduces the amount of energy available to heat the atmosphere Clouds have a high albedo Cloud cover affects daily temperature range: Clear days are warmer than cloudy, clear nights are cooler than cloudy At night, clouds absorb outgoing radiation and emit a portion back down to the surface making it warmer Cloud cover affects monthly mean temperatures: Ex: Myanmar has highest monthly means because the summer months have extensive cloud cover which reduces incoming radiation Influence of Snow and Ice: Snow and ice covered surfaces have high albedo Mountain glaciers don't melt in the summer because daytime maxes on a sunny day are cooler than they otherwise would be because the energy is being reflected and not absorbed into the land Shrinking Sea Ice: The area of the Arctic Ocean covered by sea ice is shrinking These zones are now less reflective and more absorptive The lowering of the albedo of the area is contributing to rising temperatures
Albedo Variations
If mountains are high enough they can stay snow covered year round, even if they're in the tropics Ex: Guayaquil and Quito, Quito is high in the Andes and has a lower mean that Guayaquil even though they are relatively close to each other and both near the equator High altitude places are warmer than the calculate value using normal lapse rate because of the absorption and re-radiation of solar energy by the ground surface
Altitude
Average of the 12 monthly means
Annual mean termperature
The highest and lowest mean temperatures do not coincide with the periods of maximum and minimum incoming solar radiation Indicating that the amount of solar radiation received is not the only factor determining the temperature at a particular location
Annual temperature cycles
Finding the difference between the warmest and coldest monthly mean temperatures
Annual temperature range
Temperature that a person perceives
Apparent temperature
Amount of power required to cool Determined each day by subtracting 65 degrees F from the daily mean January 1 through December 31 Meaning the accumulation since January 1 of that year
Cooling degree days
Determined by averaging the 24 hour readings by adding the maximum and minimum temperatures for a 24 hour period and dividing by 2
Daily mean temperature
The minimum temperature occurs at about sunrise An energy surplus that built up lasts for several hours in the afternoon and contributes significantly to the lag of the maximum When the input of solar energy no longer exceeds the rate of energy lost by Earth, the temperature cools In dry regions, the maximum temperature occurs quite late in the afternoon In humid regions, there is a shorter time lag for the maximum temperature
Daily temperature cycle
Finding the difference between the maximum and minimum
Daily temperature range
Different land surfaces reflect and absorb varying amounts of incoming solar energy Greatest contrast is between land and water Land heats more rapidly heats more rapidly and to higher temperatures than water Land cools more rapidly and to lower temperatures than water Water bodies warm and cool more slowly than land With no marine influence, there are greater temperature extremes Northern hemisphere is covered by less water than the Southern hemisphere which means that the Southern hemisphere has smaller annual temperature ranges
Differential heating of land and water
Thermistor(thermal resistor): its resistance to current flow varies with temperature As temperature increases so does resistance reducing the flow current As temperature decreases so does resistance increasing the flow current It is used as a temperature sensor or an electrical thermometer
Electrical thermometers
1. Water is highly mobile. Convection distributes the heat through a considerably larger mass. Heat does not penetrate deeply into soil or rock. Land uses conduction. A thick layer of water is heated to a moderate temperature and a thin layer of land is heated to higher temperatures 2. Heat is only absorbed at the surface of the land. Water allows more solar radiation to penetrate to a further depth 3. The specific heat of water is more than three greater than that of land 4. Evaporation from water bodies is greater than from land surfaces.
Factors responsible for differential heating of land and water
A coastal location where wind blows from the ocean onto shore (windward) experiences considerably different temperatures than a coastal location with winds blowing from land toward the ocean (leeward) Windward coasts have cool summers and mild winters The leeward coast winds do not carry the ocean's influence onshore Ex: NYC is leeward, so warmer Ex: Eureka is windward, so colder Ex: Seattle and Spokane, mountains acting as barriers Seattle experiences marine influence and Spokane is typically more continental The mountains cut Spokane off from the moderating influence of the Pacific Ocean
Geographic position
Used in agriculture to determine the approximate date when crops will be ready for harvest Difference between the daily mean temperature and the base temperature of the crop Starting with the onset of the growth season
Growing degree days
High humidity contributes significantly Evaporation of perspiration reduces body temperature but humidity retards evaporation Heat (stress) index: as relative humidity increases the apparent temperature and heat stress increases as well Length of exposure to direct sunlight, wind speed and general health affect the amount of stress
Heat stress
Evaluates the energy demand and consumption Each degree of temperature below 65 degrees F is counted as 1 heating degree The amount of required is proportional to the total heating degree days Can estimate differences in seasonal fuel consumption July 1 through June 30
Heating degree days
A line that connects points on a map that have the same temperature Usually a 5-10 degree difference is used Can use any interval though Makes temperature distribution clearly visible Closely spaced together means a rapid rate of temperature change Widely spaced out means a more gradual rate of change
Isotherm
The delay of the maximum until mid to late afternoon
Lag of the maximum
Meniscus: the movement of the end of the "thread" Liquid in glass: temperature rises and the liquid expands, a thin "thread" of liquid is forced up the capillary tube and when the temp falls the liquid contract Maximum thermometer: has a narrowed passage called a constriction, when temp falls the constriction doesn't allow the mercury to return to the bulb and the top of the mercury stays at the highest point Minimum thermometer: a low density liquid like alcohol is used, a dumbbell shaped index is placed at top of the column, when temp drops the index is pulled towards the bulb, when the temp rises past the index it stays at the lowest temp recorded Bimetal strip: two thin strips of metal are bonded together and have widely different expansion properties, with temp changes the metals expand or contract unequally which corresponds to temp changes Thermograph: uses the curve of the bimetal strip to move the pen arm that records the weather data, less accurate than reading obtained from a mercury in glass thermometer
Mechanical thermometers
Adding together the daily means for each day of the month and dividing by the number of days in the month
Monthly mean temperature
Energy is passed from moving air to the water through friction Major horizontal movements of surface waters are closely related to the circulation of the atmosphere Surface ocean currents have an important effect on climate Net gain of energy happens in lower latitudes, net loss of energy happens in higher latitudes *The transfer of heat by winds and ocean currents equalizes these latitudinal energy imbalances* The North Atlantic Drift keeps wintertime temperatures in Great Britain and much of Western Europe than would be expected for their latitudes Warm ocean currents like the Gulf Stream are felt most during the winter and cold currents exert their greatest influence in the tropics or during the summer months in the middle latitudes
Ocean currents
The amount of heat needed to raise the temperature of one gram of a substance by one degree Celsius
Specific heat
Any factor that causes temperatures to vary from place to place and from time to time
Temperature control
Amount of temperature change per unit of distance
Temperature gradient
Based on the use of reference points or fixed points Fahrenheit: the zero point was the lowest temperature able to be obtained with a mixture of ice, water and salt, second fixed point was the human body temperature. Ice point: 32, steam point: 212 Celsius: melting point of ice is 0 degrees and the boiling point is 100 degrees, a celsius degree is larger than a fahrenheit degree by a factor of 1.8 Kelvin (absolute) scale: similar to celsius, with 100 degrees separating the melting point of ice and boiling point of water, ice point is 273 K and steam point is 373 K, the zero point represents the temperature at which all molecular motion is presumed to have ceased (absolute zero)
Temperature scales
An instrument that continuously records temperature Minimum: sunrise Maximum: Between 2 PM and 5 PM Declines until sunrise the following day
Thermograph
Latitude Differential heating of land and water Ocean currents Altitude Geographic position Albedo variations
Types of temperature control
Locational factors and/or local weather conditions influences this Four common examples: 1. The daily temperature range experienced during a day in the high latitudes is small because of low sun angle all day 2. A windward coast is likely to experience only modest variations 3. Overcast days flatten the daily temperature curve. Nighttime temperatures are warmer than they otherwise would be because of cloudy nights 4. The amount of water vapor in the air affects this. Clear and dry means heat readily escapes at night and temperatures fall rapidly. Humid air absorbs outgoing radiation and slows nighttime cooling making the temperature not fall as fast Over a period of several weeks, random variations will occur and they are usually caused by the passage of atmospheric disturbances (weather systems) These circumstances can cause the max and min to be any time during the day or night
Variations in daily temperature range
Cooling by evaporation is heightened and the wind is acting to carry heat away from the body Windchill Temperature: how the wind and cold feel on human skin
Windchill
The effectiveness of incoming solar radiation in heating Earth's surface and the atmosphere above it is largely a function of latitude The added effect of the differential heating of land and water is clearly reflected on the January and July temperatures Warmest and coldest temperatures are found over land The north-south migration of isotherms is greater over the continent Warm currents cause isotherms to be deflected toward the poles Cold currents cause an equatorward bending The annual temperature range increases with an increase in latitude Outside the tropics the annual range will increase with an increase in continentality The tropics clearly experience small annual temperature variations Annual temperature ranges in the ocean dominated Southern hemisphere are much smaller than in the Northern Hemisphere with its large continents
World distribution of temperatures
