Incubation Data Climatology: Bird, Reptile Incubation Data Climatology, v4386

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102 Pages
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of the atmosphere is greater in winter than in summer because of the greater differences in temp. in winter. Large bodies of water tend to stabilize air temps. much more than land masses do. On land, heat penetrates very little - most of the heat is at or near the surface. In water, however, the heat penetrates deeper because of water's translucence. Also, turbulence in water tends to distribute the heat more evenly. The evaporation at the surface requires heat from water. All these factors tend to keep water temps. more nearly constant. Physical properties of air Heating or cooling of air (by expansion or compression) occurs without any exchange of heat with the outside. This is called adiabatic change, and is thermally isolated. Any air that rises, expands; it is compressed when it descends. Movement of air occurs so rapidly that it is considered adiabatic (no transfer of heat). The capacity of air to hold water vapor decreases rapidly as the air is cooled. Precipitation occurs with the cooling of moist air. Boyle's Law - for a constant temp., the volume of dry gas varies inversely as the pressure. Charles' Law - for a constant pressure, the volume of dry gas is directly proportional to the absolute temp. Expanding mass of air is cooled to the extent of the increase in volume. A contracting mass of air is heated by the work of compression performed on it. Temperature changes are considerable under these conditions. For example: an air mass expanded to 1/2 its initial pressure reduces the absolute temp. by 18%
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(~50°C. in cooling from room temp.) The dry adiabatic rate of change in temp. with increase in elevation is -1°C. for 10,293 cm. This is often rounded off to -1°C. / 100 meters, or -5.4°F./1000 ft. The maximum effect of water vapor as a gas (un-saturated) [illegible] is to decrease the rate of cooling very slightly (~1 meter). Under saturated conditions, latent heat is released at condensation of water vapor (saturation adiabatic change). This adds heat to the dry adiabatic rate. As air rises, it expands and cools until saturation and finally condensation occurs. At that point, heat is released at condensation, so there is a slower rate of cooling with more expansion. Adiabatic heating and cooling is reversible as long as no water is removed from the air by condensation. If all the water vapor is removed by condensation, the air cools according to the dry adiabatic rate, so it returns to the surface at a higher temp. than when it ascended. The greater the temp., the more condensation can be released if the air is cooled. Example: cooling from 40°C. to 20°C. can release much more condensation than cooling from 20°C. to 0°C., even though the temp. difference is the same in both cases (it is not a straight line function). Lapse rate is the actual observed readings of temp. as altitude changes. It may or may not be the same as dry adiabatic rate. Lapse rate is considered positive if the temp. decreases with height. In the lower atmosphere the lapse rate usually but not always is positive. If temp. increases with rise in elevation, it
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is called a negative lapse rate (inversion). If an air particle is warmer than its surroundings, its density will be less, so it will accelerate upward. If the particle is cooler than its surroundings, it will accelerate downward. The rate is determined by the difference in temp. of the air particle and its surroundings. All vertical motions in the atmosphere tend to be accelerated in the same direction because of the increasing temp. difference between the particle and its surroundings. At the wet adiabatic rate the difference is increased even more than at the dry adiabatic rate. Therefore, acceleration is greater in moist than in dry air. Air Stability Conditions 1. Stable equilibrium -- this occurs when the prevailing lapse rate is less than the wet adiabatic rate (thus, the air particle is always colder than its surroundings). This occurs when the ground surface is colder than the air above. This happens in winter over the continents in middle and high latitudes, and over the oceans in summer. Winds are free of vertical turbulence, so there is little or no precipitation. 2. Conditionally stable (or unstable) equilibrium -- the lapse rate is greater than the wet adiabatic rate, but less than the dry adiabatic rate. It is a stable condition for unsaturated air, but unstable for saturated air. It occurs when the ground surface is warmer than the air. It occurs mostly in low latitudes, over continents in summer and over the ocean in winter in mid-latitudes. This condition produces turbulent storms, with lots of precipitation when the air is near or at saturation.
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3. Neutral equilibrium - the lapse rate equals the dry adiabatic rate. Under these conditions, saturated air is unstable whereas unsaturated air is stable. This situation almost never occurs. 4. Unstable equilibrium - the lapse rate is greater (steeper) than the dry adiabatic rate for either saturated or unsaturated air. The air particle is warmer than its surroundings. Therefore, it continues to rise. This condition occurs less frequently than #1 & 2. It is restricted to the lower atmosphere (2-3 kilometers) in arid or semi-arid continental areas during periods of maximum heating of the surface. This condition produces local thunderstorms in summer, but doesn't produce any widespread storms. 5. Auto-convective equilibrium - the lapse rate exceeds -3.42°C./100 meters (-19°F./1000 feet). This is a rare occurrence. It results from a shallow layer of air above a strongly heated surface (sand, pavement, etc.). It is very local in extent. It produces an overturn of air without any outside source of energy. It represents extreme instability, and produces such things as "dust devils". Any layer of air of a particular thickness will expand to a greater thickness or be compressed to a lesser thickness. A sinking layer of air spreads horizontally, while a lifted layer of air is exposed to vertical stretching. A sinking and horizontally spreading layer increases air stability (the top of air layer is heated more than the bottom of the layer by adiabatic heating). Lifting air decreases stability, since the bottom of the layer
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Condensation can not occur in air that is throughly free of all impurities. Water molecules must have particles of some sort on which to condense (condensation nuclei). Such things as dust, smoke, soot, industrial pollution (smog), sea salt from ocean spray (most common hygroscopic material in the air) are often utilized by water particles. Large particles of water are formed by the addition of other small particles. This is produced by strong vertical motion of the air. Under these conditions ice crystals form very quickly. As they fall, they melt, thereby forming a rain drop. Saturation is produced by cool or cold air being brought over a warm surface. This brings about saturation very quickly, producing visible steaming (fog over sweet Lakes, Arctic "smoke", etc.). Saturation also is produced when cooling air with a given water content is cooled to a low enough temp. that saturation vapor pressure is reached. This is the more important of these 2 processes. Condensation occurs on a solid surface that is colder than the dew point of the air to which it is exposed. Example: dew forms on a cold night, but if the temp. is below the freezing point, frost occurs. There are four processes by which air is cooled below dew point: 1) Cooling by conduction of heat to a cold surface 2) Direct radiational cooling of air 3) Mixing of warm and cold masses of saturated air 4) Cooling by adiabatic expansion In hilly areas, cold air drains to low spots in the valleys at night, producing inversions in such places.
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11. lows, counterclockwise around highs). Cells are usually in mid-ocean or mid-continent, not at the boundary between. Sub-polar oceans strengthen lows in winter due to the higher temperature of water relative to near-by land masses (ex: Alaska). Strong highs occur over sub-tropic oceans in summer for the reverse reason. Over continents there is a reversal of pressures in the change of seasons. Sub-tropical highs exist over large ocean areas throughout the year. The Aleutian low in the north Pacific and the Icelandic low in the north Atlantic are the major lows of the northern hemisphere. Types of fronts 1. Secondary fronts are formed orographically when a mountain barrier is lying across a strong wind. This creates a ridge of slightly higher pressure on the windward side, a slightly lower pressure on the lee side. This is a relatively unimportantant type of front. It may be important in the amount of precipitation that falls, but changes in pressure is not the cause (ex: east of Rockies, east of Appalachians, east of Sierra Nevada). No real front present. 2. Secondary front with a true front - a low pressure trough and frontal system tend to persist for some time (ex: east of Rockies in winter). It is due to strong maritime polar air from the Pacific. The temperature contrast is quite sharp - it is a warm, dry front. When this air collides with maritime (Gulf of Mexico) air, squalls and thundestorms result. This type is not too important. 3. This type of front results from the close proximity of two air masses of quite different temperatures. It usually results when continental polar air (cold) from the Canadian shield comes into contact with maritime Caribbean air (warm)
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12. in middle and eastern United States. Frontal zones are formed on the eastern side of the continent. The lows move along the polar front to the east. The cold, heavier air tends to under-run the warm, lighter air. This is called the zone of contact or surface of discontinuity. There are opposite winds on the two sides of the front (east on cold northern side, west on warmer southern side). When the movement is toward the warm air mass, cold air replaces the warm air (cold front); when movement is toward the cold air mass, warm air replaces cold air (warm front). It is an active front when the warm air is forced upward over the cold air to the point where condensation may occur (relative motion between the two). 4. In a passive front, no clouds form and no precipitation occurs. In a warm front the cold air mass recedes as fast or faster than the warm air approaches. In a cold front, the reverse occurs. A warm front has cirrus clouds well in advance of the front. Then alto-stratus clouds, which can produce snow, follow, in turn followed by nimbus clouds that provide rain just in advance of the front. This is due to warm air moving more rapidly than the cold air beneath. Both cold and warm fronts can be moving at the same time. Fronts are produced by changes of winds, or changes of temperature gradients. Extreme local heating or cooling (large seasonal contrasts) produce thermally-caused secondary circulations. The larger the size of continents in mid-latitudes, the greater the seasonal circulation there will be.
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Geography IA The Climatic Symbols of Köppen (1936) (Monthly temperatures in this table mean average monthly temperatures. The high sun, or summer, season for northern hemisphere stations is May-October; low sun, or winter, November-April) Symbol Name Definition Description Remarks A tropical coldest month over 18°C (64.4°F) no winter For A climates B dry evaporation exceeds precipitation too dry for growth of forests For C & D climates & dry humid test (chart #1) BS steppe) see chart #1 at end of table precipitation insufficient for forests; grass and open brush in- stead. Precipitation very low, vegetation very scanty. BW desert) mild winter C mesothermal coldest month between 18°C and -3°C (64.4°F & 26.6°F) and at least one month over 10°C (50°F) severe winter, snow cover or fro- zen ground for at least a month D microthermal coldest month below -3°(26.69F); at least one month over 10°C (50°F) no summer, no trees E polar no month over 10°C (50°F) warmerest month above freezing, some vegetation ET tundra warmest month between 0° & 10°C (32° & 50°F) EF frost no month above 0°C (32°F) perpetual frost, lifeless m transition monsoon w in precipitation, f in vegeta- tion, see chart #2 end of table dry in winter with high yearly rainfall and rain forest w low-sun dry see chart #2 at end of table dry in vinter, precipitation mainly in summer half year w winter dry driest month less than 3 cm. and rainiest summer month 10x precipi- tation of driest winter month
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