Formation Easterly Wave. Tropical cyclones often develop along easterly waves. These waves, or oscillations, in the trade winds move from east to west across the tropics. As low-level winds enter the trough of the wave, they converge, causing convection. What are the strongest storms on Earth? Shortly after midnight on October 23, , a group of courageous men and women flew into the center of Hurricane Patricia and landed in the history books. With measured winds of MPH, Hurricane Patricia became the strongest tropical cyclone ever recorded anywhere on Earth.
How does air flow in a hurricane? Tropical cyclones are like giant engines that use warm, moist air as fuel. That is why they form only over warm ocean waters near the equator.
The warm, moist air over the ocean rises upward from near the surface. Because this air moves up and away from the surface, there is less air left near the surface. What force is a hurricane? What is the most destructive type of storm on Earth?
August , November , February , March 18, When the sun heats the ground, the warmed air at the surface will rise under the influence of convection.
The rising thermals are similar to the hot bubbles of water that rise from the bottom of a boiling pot. If the air is stable, then the bubbles of warm air will form scattered fair weather cumulus clouds and not much else. If the air is unstable, then the lifting from convection will lead to rapid growth of clouds into deep cumulonimbus clouds, or thunderstorms.
The higher the surface temperatures, the more convection can occur. Precipitation in the Southeast is influenced by a variety of lifting mechanisms. The prevailing winds in that region are mostly from the south and west, and Lake Toxaway is on the windward side of the Appalachian mountains, making orographic lift an effective precipitation mechanism.
Figure E. Air Converging Inland Over Florida. Image from the American Meteorological Society. A classic example of air converging and forming rain showers and thunderstorms is the sea breeze in Florida.
During the summer, sea breezes will often form on the west and east sides of Florida. As the two sea breezes move landward on the Florida peninsula, they collide with each other, and the air is forced to move upward. Wherever the two sea breezes collide, there is often intense rainfall and thunderstorms, and this provides much of the summer rain for many parts of Florida. Convective lift is the most common form of lift in the Southeast during the summer since fronts do not pass through as often as they do during the rest of the year.
If the air is moist enough as it usually is during the summer , thunderstorms can form and provide rainfall to crops and plants. Uplift of the air may continue several kilometres before losing buoyancy, forming large towering clouds called cumulonimbus see Figure 6. Under such conditions, the atmosphere is said to be unstable.
In general, a northerly air stream, moving southwards in the northern hemisphere and therefore warming at its lower level, will have a large temperature range with height and be unstable. Conversely, a southerly air stream, moving northwards and therefore cooling at its lower level, will have a relatively narrow temperature range with height and be stable. Generally, cumulus clouds forming in stable air produce no precipitation.
During the formation of the larger cumulonimbus, condensation droplets are carried up and down several times within the convection currents inside the cloud before being released, generally coalescing to form rain drops. The more vigorous the thermal currents inside the cloud, the larger the rain drops which form. Light showers can fall form modest-sized "cauliflower" clouds whilst the larger cumulonimbus clouds can produce heavy downpours.
The largest cumulonimbus clouds of all are found in thunderstorms. In these clouds, up-currents are so severe that splitting of rain drops and ice crystals can occur before re-coalescing and falling to the ground. It is believed that this may contribute to the build up of electric charge and the occurrence of lightning. When huge masses of air come together from different directions, uplift and cooling of air with cloud formation and rain can occur, if differences exist in temperature and humidity between the two air masses.
They cannot mix together immediately owing to their different densities, any more than two liquids like water and oil. Mixing takes time. In the meantime, the lighter, warmer air mass begins to rise above the cooler, denser one.
The boundary between the two air masses is called a front. Fronts are usually several hundred miles long and emanate from the centre of low pressure systems or depressions. There are warm fronts, cold fronts and occluded fronts. A warm front exists when warm air is rising over cold air. In vertical cross-section, the boundary takes the form of a gradual slope roughly and lifting is slow but persistent.
As the air lifts into regions of lower pressure, it expands, cools and condenses water vapour as flat sheet cloud altostratus , from which rain can start to fall once cloud has thickened to about 2,m from the ground. Cloud continues to lower towards the boundary at ground level, known as the surface front.
This lower level cloud is called stratus or nimbostratus, from which appreciable amounts of rain may fall. Sometimes, nimbostratus cloud may be only a few hundred metres above the ground, and can completely cover hill tops and mountains. Because frontal systems have a velocity of their own, an observer on the ground will witness a succession of cloud types with cloud gradually thickening before rain arrives see Figure 6. These tell-tale signs can be used by the observer to predict the onset of bad weather within a few hours.
Lifting Mechanisms that Form Clouds - Most clouds form when air cools to the dew point as a parcel of air rises vertically. Cloud Classification - Clouds are given names corresponding to their appearance, layered or convective, and their altitude, as well as if they are precipitating.
Precipitation - Precipitation is any liquid or solid water particles that falls from the atmosphere and reaches the ground.
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