Global Wind Circulations
AT THE EQUATOR, a band of RISING AIR, Low Pressure develops due to High Insolation Receipts, called the INTERTROPICAL CONVERGENCE ZONE (ITCZ) Bands of clouds Where the Midlatitude Westerlies and Polar Easterlies meet. where the polar easterlies meet warm air from the westerlies, a stormy region known subtropical high pressure zones, around 30 degrees latitude created by . Prevailing winds are winds that blow predominantly from an individual direction over a particular point on the Earth's surface. The dominant winds are the trends in direction of wind with the highest speed over a particular point on the Earth's surface. A region's prevailing and dominant winds are enacted by global patterns of Together with the trade winds, the westerlies.
This rising air over the land lowers the sea level pressure by about 0.
The cooler air above the sea, now with higher sea level pressure, flows towards the land into the lower pressure, creating a cooler breeze near the coast. The strength of the sea breeze is directly proportional to the temperature difference between the land mass and the sea. At night, the land cools off more quickly than the ocean due to differences in their specific heat values, which forces the daytime sea breeze to dissipate.
If the temperature onshore cools below the temperature offshore, the pressure over the water will be lower than that of the land, establishing a land breeze, as long as an onshore wind is not strong enough to oppose it. The wind flows towards a mountain and produces a first oscillation A. A second wave occurs further away and higher.
The lenticular clouds form at the peak of the waves B. Over elevated surfaces, heating of the ground exceeds the heating of the surrounding air at the same altitude above sea level, creating an associated thermal low over the terrain and enhancing any lows which would have otherwise existed,   and changing the wind circulation of the region. In areas where there is rugged topography that significantly interrupts the environmental wind flow, the wind can change direction and accelerate parallel to the wind obstruction.
Jagged terrain combines to produce unpredictable flow patterns and turbulence, such as rotors. Strong updraftsdowndrafts and eddies develop as the air flows over hills and down valleys. Wind direction changes due to the contour of the land.
If there is a pass in the mountain range, winds will rush through the pass with considerable speed due to the Bernoulli principle that describes an inverse relationship between speed and pressure.
The airflow can remain turbulent and erratic for some distance downwind into the flatter countryside. These conditions are dangerous to ascending and descending airplanes. At night, the sides of the hills cool through radiation of the heat.
Hadley cell Sunlight heats the air in tropics more than the poles, causing a temperature gradient change of temperature across a distance between the equator and the poles. The warmer air near the equator rises and creates a region of heavy rain and thunderstorms called thethe Intertropical Convergence Zone ITCZor the Doldrums. Horizontal winds are are often light to calm, making it difficult to sail at the ITCZ. This warm air rises to the top of the troposphere, and spreads out toward the Northern and Southern Hemispheres.
This turning is due tothe Coriolis effectwhich is related to the rotation of the earth. Air accumulates here, and creates a subtropical high pressure zone. This is another region of light to calm surface winds where it is difficult to sail. In the old days when sailing ships were becalmed in this region, the ships often ran out of food and fresh water, causing any animals such as horses on board to die.
These latitude bands became known as the horse latitudes.
Prevailing winds - Wikipedia
The descending air is very dry, so these latitude bands are where deserts are favoured in both the Northern and Southern Hemisphere. As surface air blows back toward the equator, it is turned to the right in the N.
Hemisphere, and to the left in the S. Hemisphere, due to the Coriolis effect. The result are the trade winds winds with a component from the east over the ocean surface. The figure below shows the Hadley cells. Idealized global circulation for Northern Hemisphere winter. The bulls-eye symbol indicates where a jet stream is coming out of the page toward the reader, and the "X" with a circle around it represents imagined tail feathers of jet-stream wind flowing into the page.
Note that the tropopause is the boundary between the troposphere, where our weather events take place, and the stratosphere, where the air is mostly dry. The stratosphere acts like a lid or cap on the weather that we experience in the troposphere.
Global Wind Circulations
Mid-latitude Cyclones At mid-latitudes, such as Canada, there is not a strong vertical circulation cell. Instead, the winds create large, horizontally swirling low- and high-pressure systems that we see on weather maps see figure below. High-pressure regions, called anticyclones, are associated with fair weather, clear skies, but light winds not good for sailing. Low-pressure regions, called extratropical cyclones, are associated with fronts, bad weather, and strong winds not good for pleasure sailing.Global Wind Belts
Often the best sailing at mid latitudes is in between the highs and lows, where the winds are moderate and weather is still OK. The Coriolis effect causes winds rotating counterclockwise around lows in the N.
Hemisphere, and clockwise around highs. These circulations are superimposed by a general west-to-east movement of all the air at mid-latitudes. Winds are named by where they come from.