Precipitation-producing conditions - Thus so far we have observed that precipitation results when air rises and is adiabatically cooled below the dew point so rapidly that not only do clouds form, but rain, snow, or hail is produced as well. Consider, then, how large masses of air re actually induced to rise to higher elevations. The three possible ways are
(1) convectional,
(2) orographic, and
(3) cyclonic or frontal.
Convectional precipitation - Convectional precipitation results from a convection cell, which is simply an updraft of warmer air, seeking higher altitude because it is lighter than surrounding air.
Suppose that on a clear, warm summer morning the sun is shining upon a landscape consisting of patches of open fields and woodlands. Certain of these types of surfaces, such as the bare ground, heat more rapidly and transmit radiant heat to the overlying air. Air over a warmer patch is thus warmed more than adjacent air and begins to rise as a bubble, much as a hot-air balloon after being released. Vertical movements of this type are often called thermals by sailplane pilots who use them to obtain lift.
As the air rises, it is cooled adiabatically so that eventually it will reach the same temperature as the surrounding air and come to rest. Before this happens, however, it may be cooled below the dew point. At once condensation begins, and the rising air column appears as a cumulus cloud whose fiat base shows the critical level above which condensation is occurring. The bulging 'cauliflower' top of the cloud represents the top of the rising warm air bubble, pushing into higher levels of the atmosphere. Usually the small cumulus cloud dissolves after drifting some distance downwind. However, should this convection continue to develop, the cloud may grow to a cumulonimbus mass, or thunderstorm, from which heavy rain will fall. Why, you may ask, does such spontaneous cloud growth take place and continue beyond the initial cumulus stage long after the original input of heat energy is gone?
Actually, the unequal heating of the ground served only as a trigger effect to release a spontaneous updraft, fed by latent heat energy liberated from the condensing water vapour. Recall that for every gram of water formed by condensation 600 calories of heat are released. The small circles represent a small parcel of air being forced to rise steadily higher, following the same dry adiabatic rate of cooling. To the right of this line is a solid line showing the temperature of the undisturbed surrounding air; it is the environmental lapse rate.
Suppose that the air parcel is lifted from a point near the ground, where its temperature is 90° F (32° C). After the air parcel has been carried up 2000 ft (600 m), its temperature has fallen about 11° F (6° C) and is now 79° F (26° C); whereas the surrounding air is cooler by only about 7° F (4 °C), and has a temperature of 83° F (28° C). The air parcel would thus be cooler than the surrounding air at 2000 ft (600 m), and if no longer forcibly carried upward, would tend to sink back to the ground. These conditions represent stable air, not likely to produce convectional rise, because the air would resist lifting.
When the air layer near the ground is excessively heated by the sun, the environmental lapse rate is increased. The air parcel near the ground begins to rise spontaneously because it is lighter than air over adjacent, less intensely heated ground areas. Although cooled adiabatically while rising, the air parcel at 1000 ft (300 m) has a temperature of 85° F (29° C), but this is well above the temperature of the surrounding still air. The air parcel, therefore, is lighter than the surrounding air and continues its rise. At 2000 ft (600 m), the dew point is reached and condensation sets in. Now the rising air parcel is cooled at the reduced wet adiabatic rate of 3.2 ° F per 1000 feet (0.6° C per 100 m), because the latent heat liberated in condensation offsets the rate of drop due to expansion. At 3000 ft (900 m), the rising air parcel is still' several degrees warmer than the surrounding air, and therefore continues it spontaneous rise.
The air described here, as spontaneously rising during condensation is unstable in properties. In such air the updraft tends to increase in intensity as time goes on, much as a bonfire blazes with increasing ferocity as the updraft draws on greater supplies of oxygen. Of course, at very high altitudes, the bulk of the water vapour having condensed and fallen as precipitation, the energy source is gone; the convection column then weakens and air rise finally ceases.
Unstable air, given to spontaneous convection in the form of heavy showers and thunderstorms, is most likely to be found in warm, humid areas such as the equatorial and tropical oceans and their bordering lands throughout the year, and the middle-latitude regions during the summer season.
Locals hypothesize that the legacy of Italian blood and culture in Cologne, colonized by the Romans more than 1500 years ago, makes the people more jovial and lighthearted. Cologne is the largest city on the Rhine.
Kolsch is not only the dialect spoken here but, also the name of their own top-fermented beer. There are more than 4,000 pubs, restaurant's and brewery taverns in Cologne.
Unlike many of the world's large cities, Cologne, with a population of over a million, gets better every day, there are more things to do and see, more new and innovative buildings... more
Travel is an opportunity to learn, whether geography, languages, history or other subjects.
Cologne is situated on the beautiful Rhine River.