Sunday, April 18, 2010

The Weather Channel Web Site

Recently the Weather Channel in Australia spent and great deal of time (and money!) doing a complete remake of its website.

You can see the result at

It's a revolutionary way of retrieving weather information from the Internet, utilizing a single page from which all other content can be accessed. This means that you don’t have to move from page to page – it’s simple and easy.

A really great feature is being able to go full screen with the satellite images, radar, and lightning tracker. You can also zoom in and out by rolling your mouse wheel – really quick and useful.

The cloud resolution is great – you can see fog clearly, which is often difficult in conventional displays.

Fog can clearly see seen on the new Weather Channel interactive map.

(Click on image to enlarge)

Some of the key issues the page offers are:

All your local weather information is combined into one page. There’s no more hunting through pages of content – you’ll have all the information you need – whether it’s the ten-day forecast, the radar or the rainfall probability at a single glance.

It offers you instant access to your local weather- the computer detects where you are, and instantly displays the weather information for that location.

A revolutionary Interactive map – displays satellite and radar data from both the past and future 24 hours and so you can track how storms move over time. You can manipulate the map to move between different locations, zoom in and out and even make it full-screen for a truly breath-taking experience of the weather.

It’s advantages to users are:

Ease of use –
No more hunting through layers of content to get the weather forecast, displays all your essential weather information in one page – so you’ll have everything you need in a single glance.

Furthermore, whilst other websites divide up the radar views into separate pages, The Weather Channel site has combined all radar information in their truly interactive map, meaning that users can watch the rain move across broader areas in a single glance.

Speed –
The new website is fast to use – thanks to cutting-edge geotargeting technology. It recognises where you are accessing the site from and takes you instantly to the weather information for your location.

Increased Interactivity – is the first Australian weather website to feature a comprehensive interactive weather map which combines weather observations and forecasts, radar, satellite and lightning information all in the one view. Users have the option to view the map full screen and can easily zoom in and out to view weather activity at both a national and more local level.

Sunday, April 11, 2010

Jet Streams and Tropical Cloudbands

Jet streams

Early in the twentieth century, meteorologists predicted that there would be high-speed rivers of air in certain areas of both hemispheres at around the area of the tropopause, approximately 10 to 15 km above the surface. They posited that these would be a consequence of the physics of the rotating Earth–atmosphere system.

The German meteorologist H. Seilkopf is believed to have first used the term “strahlstromung” (jet stream) in a treatise on upper atmospheric flow in 1939. However, it was not until World War Two that anyone directly encountered these ‘jet streams’. Aircraft on high-level bombing missions over Europe and Japan encountered tremendous headwinds on occasion, up to 350 km/h, which was almost as fast as the aircraft of the day could fly. Some of the planes were virtually stationary in the sky as they flew head on into the jet streams.

Today we know that jet streams are indeed real, and they are an important part of the motion of the atmosphere. There are two main jet streams in each hemisphere, called the polar jet and the subtropical jet. They rotate in a general west to east direction high above Earth, but they frequently twist and turn, producing meanderings of north and south winds on occasion. There are times where the polar jet and subtropical jet can intersect, producing highly complex effects in the upper troposphere.

The subtropical jet is found at latitudes around 25 to 35 degrees north and south of the equator, and the polar jet between the 50 and 60 degree latitudes. All these jet streams occur at the boundaries of cold and warm air in the upper atmosphere and are typically 1.5–4.5 km across.

A jet stream made visible by cloud as it crosses eastern Canada in May 1991. Jet streams can make a significant difference in flying times across Australia. If favoured by a jet stream, a flight from Perth to Sydney can take half an hour less than the reverse trip, Sydney to Perth. (NASA Space Shuttle image - click to enlarge)

They are of considerable importance in the development and steering of low-pressure systems, and meteorologists pay careful attention to their location and general movement. The aviation industry is also very interested in jet streams because of their effect on flight times. For example, when travelling from Perth to Sydney, ‘hitching a ride’ on the high-level subtropical jet stream can save significant time and fuel. Conversely, flying into the jet stream will slow the ground speed of the aircraft considerably, and in many cases the captain will attempt to fly above or below it to save time.

Another problem with the jet stream is its association with high-level clear air turbulence—or CAT—which can be uncomfortable or downright dangerous for passenger aircraft. Because jet streams are zones of high-speed winds running within the broad-scale atmospheric flow, there are surrounding regions where the wind speeds change quickly with both height and horizontal distance. This is called wind shear and a high-speed aircraft flying through it will experience ‘bumpiness’, something like a car driving over a series of potholes. This is called turbulence.

In most cases turbulence is only slight, but sometimes severe buffeting can occur, sufficient to throw objects around the cabin and injure passengers.

Tropical cloud bands

Jet streams play an important role in the generation of tropical cloud bands that periodically develop near the equator and then move to the mid latitudes—from the southwest in the northern hemisphere and the northwest in the southern hemisphere.

These cloud bands are the result of complex interaction between warm sea surface temperatures and upper wind patterns, notably the subtropical jet streams. They are important sources of rain in some mid-latitude areas, including Australia, where they are known as northwest cloud bands.

A northwest cloudband streams across Australia on 30th July 2008.
(Bureau of Meteorology image - click to enlarge)

In a large part of western and central Australia, more than 60 per cent of the April–October rainfall is contributed by northwest cloud bands that form to the south of Indonesia before streaming in from the northwest to form a cloud ‘conveyor belt’ that can be between 3000 and 8000 km long.

When a northwest cloud band interacts with a cold frontal system over southern areas of Australia, significant inland rain can result.

Reference: The Complete Book of Australian Weather by Richard Whitaker
Allen and Unwin 2010, ISBN978 1 74175 734 7