III. Earth's Winds
Earth’s Winds Meteorology & Oceanography
stands out particularly well, working in tandem Pressure Systems and Winds III. Earth’s Winds with the Asian monsoon. Furthermore, thermals January as well as channelling and venturi effects enhance L l y L L he driving force behind the wind is the range of room is available on the high seas for the lows to develop the prominent windy points on the Horn of t e r We s s i n d H temperatures at Earth’s various latitudes. They cause into fully fledged storms, hence the more radical conditions Africa and Gulf of Bengal in July. The winter W H Westerly t s air pressure differences, which in turn create wind. The will be. In contrast, summer winds and waves are much more (January) NE Monsoon is visibly weaker. s H W i n d N a s M o T t E d
t r s diagrams on the previous spread (chapter II) show how and at modest. The trade winds around 20° North are plain to see Western Australia’s coast is consumed n s o t h i s n d t a n r t h W a n s o E o a s i which latitudes the bands in the Caribbean and by the westerly wind zone in austral e E s
N h d E o o W d rt n h o i s W
a o t rd r N W e
e h n
September 23 n r T d s e
of pressure form. Naturally, Gulf of Mexico. They’re winter (July), whereas a veil of sea ra t o T t equinox o d r N a maximum insolation o r
in practice there’s a raft stronger in the southern breeze bolstered by a heat low over the Doldrums M T at the equator S S st o u o N June 21 t T u m s of other key factors. The Caribbean in winter when continent is plain to see in summer. T h r th a l r a E ad C summer solstice d a e E e s L W a distribution of land and sea maximum insolation the increasing pressure W t s L So i i t u at the Tropic n n T t d d r h L s ad E of Cancer s e a has the greatest influence difference to the heat low In the Pacific, pressure charts and W s t in d on seasonal temperature over Central and South satellite measurements are equally s H H H W differences, and hence wind Sun America is conspicuous. impressive. Once again, huge storms e s t e r l i e s 1040 hPa W e s t e r creation both regionally To the south you can see rage in the Northern Hemisphere’s l i e s L and globally. Landmass the belt of calmer air, westerly wind zone between 30° and 60° December 21st and continents tend to winter solstice the ‘Horse Latitudes’, South in winter (January) – albeit not as strong maximum insolation hinder the development at the Tropic of Capricorn particularly in July. South as the North Atlantic. Nevertheless, they deliver and movement of weather of the equator, SE trade super-size swell to North America, Hawaii and L st systems too, while the March 21 winds blow towards the even way down to the South Seas. Meanwhile esterly equinox W inds W i n d s oceans offer no such maximum insolation Brazilian mainland. In the Southeast Asia’s faithful wind machine, W r l y at the equator H t e 990 hPa L e s impediment. In addition, second half of the year the strong NW Monsoon dominates the W Change of Seasons H L geographical barriers can there’s obvious thermal western Pacific. The South China Seas t The intensity of sunshine differs in the Therefore the angle of incoming s s t s d a s e alter the wind’s direction, strengthening around exhibit sharp peaks of wind in January. in E d Northern and Southern Hemispheres. solar radiation differs at any given W N o r t h i n W n de e W o That’s because the Earth’s axis is tilted, point across the Earth’s surface. This ra T r a d h o strengthen it in a venturi, Ceara. Similarly easy to spot are the high NE st T L t s and thus the angle between the plane of results in the seasonal temperature North Ea D o l d r u m s u n or completely block it on Trade winds in the South trade winds in Hawaiian summertime, D o l d r u m s o o C a l m Earth’s orbit around the sun and the plane contrast and also affects atmospheric S S S s o ou M of the equator varies by 23.5° through circulation. After summer solstice – 21 u T t T t h ra h S a larger scale. All these Atlantic are noticeably you can even see the volcanoes’ wind r a d T o the year. This tilt and Earth’s annual June in the Northern Hemisphere – the d E e E r u e a W a a th W s s de processes simply can’t orbit around the sun create the seasonal point of maximum insolation gradually lighter than in the other shadow. In contrast the eastern Pacific t i t E i n W a n d i s change between summer and winter. creeps south until winter solstice on d s n t interact in exactly the oceans. Also easily is less rich in trade winds throughout s d Over the course of a year, the point of 21 December. This essentially drives s H H same way, or at the same maximum solar irradiation crosses the the migration of the global climate identifiable in the southern the year. Again we can easily see the H H H place, every time within equator twice on its travels between the machinery complete with its wind and summer are the strong SE strong winds of the westerly wind zone Tropics of Cancer and Capricorn. weather phenomena. such a constantly moving winds on the edge of the blowing all year round between New medium as the atmosphere. Yet with analysis of weather data subtropical high pressure zone on southern Africa’s west coast. Zealand and South America, and how they L July collated over the generations, at least it’s possible to depict Once again there’s visible thermal strengthening because of the shift much further north of Cape Horn in winter roaming huge distances, they’re spawned in the regions of the typical worldwide pressure and wind systems through large temperature difference between the cold ocean waters and (July). They go on to deliver stormy winters to the chilly South Earth where large bodies of water are warmed to over 26°C the seasons. And high-resolution wind measurements taken hot interior. The westerly wind zone below exhibits a lot less American coasts, sending top-quality swell into the South Seas for extended periods of time. And that’s the case at the Tropics from satellites for a couple of decades now allow a worldwide storm activity in summer (January) than in winter (July) when and even as far as Hawaii’s south coasts. The higher resolution of Cancer and Capricorn in late summertime when the sun’s overview of the actual windspeeds on our planet too. it shifts northwards. satellite pictures show powerful southerly winds along the overhead for the longest time. It evaporates massive amounts South American west coast, especially in summer (January). of water, initially as clouds that rotate around the low’s centre The North Atlantic lives up to its reputation as the windiest The Southern Hemisphere’s winter storms are strongest in the They’re created on the edge of a stable Pacific high, thermally until they reach windspeeds of 135 knots or more. There are and roughest ocean, with average (!) winter winds of up to 35 southern Indian Ocean. Unimpeded, the storms tear through reinforced the cold waters and hot land, and perfectly tropical storms in all the world’s oceans apart from the South knots and swell heights up to 10m and beyond. The further the Roaring Forties, Furious Fifties and Shrieking Sixties channelled by the Andes. Atlantic, which is too cold. They’re called hurricanes in the the westerly wind zone moves south in winter, the more around Antarctica. Further north, the tropical islands from Atlantic and East Pacific, cyclones in the Indian Ocean and
0 1 2 3 4 5 6 7 8 Beaufort9 Mauritius10 to11 Indonesia score the resulting big swell. At the Tropical storms aren’t as readily represented by this average South Pacific, typhoons in the Asian Pacific, and willy-willies Average Wind Speed same time the trade wind zone north of the Tropic of Capricorn windspeed data. Restricted to certain times of year and in Australia. 0 10 20 30 40 Knots 50 60 f NASA o y tes ur o : C
January April July October ase B ata D
16 THE WORLD KITE AND WINDSURFING GUIDE THE WORLD KITE AND WINDSURFING GUIDE 17