Up and away

Up, up and away in my beautiful, my beautiful balloon…

So the song goes, but what’s it actually like way up high in the atmosphere? Could we humans live up there if we wanted to, or had to?

I recall David Attenborough doing a great documentary in the series “The Living Planet” (“The Sky Above” episode, BBC) where he ascended beneath a very large hot-air balloon, complete with oxygen mask and equipment for sampling for life specimens. It was surprising to discover that small insects could be whisked up there and freeze, before descending again and reviving.

In this post, let’s take a closer look at what the atmosphere is like above New Zealand.

The outer limit of our weather: 10 km above sea level

This is the cruising height for large jet aircraft, and the top of Mount Everest almost reaches this height. All clouds at this altitude are frozen (that is, they are made up of ice crystals). Clouds composed of ice crystals have a wispy appearance and are known as cirrus. The tropopause, which marks the top of the troposphere, occurs at about this height. The winds are usually very strong at this level.

Air pressure: 250 hPa, one quarter of what we experience at the Earth’s surface
Temperature: about -55 °C (perhaps on a long-haul flight you’ve noted on an in-flight air show similar outside temperatures)
Air density: 400 grams per cubic metre of air
Amount of water vapour: a tenth of a gram of vapour for every kilogram of air

 

 

 

The middle levels: 5 km above sea level

Most of our rainfall is produced in clouds at around this level, where there are often large regions of rising air currents. The deep rainy clouds are nimbostratus, and other shallower types are altostratus and altocumulus. Rain or hail can fall from cumulonimbus clouds, where the air rises strongly but over a smaller area. Clouds may or may not be frozen – they may be composed of ice crystals or super-cooled water droplets (liquid water at temperatures below freezing).

Smaller passenger aircraft connecting cities within NZ often fly at around this altitude. At this height there’s less oxygen in the air, but people in some parts of the world. e.g. Tibet and the Andes, are still able to live in these conditions.

Air pressure: about 500 hPa, half of what we experience at the Earth’s surface
Temperature: about -25 to -15 °C
Air density: 700 grams per cubic metre of air
Amount of water vapour: 1 gram of vapour per kilogram of air

 

 

 

 

The lower levels: 3 km above sea level

The middle-level clouds can extend down to this level. Large cumulus can bubble upwards to this level too. Because NZ is mountainous, the clouds are often shaped by the air as it flows over the mountains. Clouds are generally not frozen (that is, they are made up of liquid water).

Mount Cook rises to just above this level.

Air pressure: about 700 hPa
Temperature: variable, but usually between -10 and +5 °C
Air density: 900 grams per cubic metre of air
Amount of water vapour: from 1 to 5 grams of vapour per kilogram of air

 

 

 

 

 

The Earth’s surface: close to sea level

Air pressure: typically between 980 and 1030 hPa (sometimes there are extremes outside this)
Temperature: highly variable, usually between 0 and 30 °C
(extreme highs are often due to the Foehn wind)
Air density: 1.2 kilograms per cubic metre of air
Amount of water vapour: highly variable, from 5 to 15 grams of vapour per kilogram of air.

The illustration shows two common types of low altitude clouds. You can see more pictures of these and other cloud types in the MetService cloud poster.

 

You may be wondering what lies above the tropopause. Above this level you’d enter the stratosphere. To give you an idea, at 15 km above sea level the air pressure is about 100 hPa, temperature interestingly remains fairly steady at about -60 °C, and the water vapour content is negligible.

Within the stratosphere is the ozone layer which, fortunately for us, absorbs most of the harmful ultraviolet light from the sun. By the way, note the similarity in the words “stratosphere” and “stratus”. Both originate from the Latin word for “layer” – the stratosphere is resistant to vertical motion so tends to have a layered structure, and stratus cloud has a somewhat layered appearance.

So far I’ve confined this post to NZ. Towards the tropics the temperature obviously rises, but it’s a little known paradox that the coldest of all tropospheric temperatures are in the tropics at about the altitude of the tropopause there (around -80 °C).

I think it’s interesting to compare the conditions at the surface with which we’re familiar, with those higher up. At what altitude do you think you could still function? Going up, up and away in a beautiful balloon is a wonderful thought, but make sure you go prepared for the conditions!

New Sun Protection Alert will help protect Kiwis’ skin this summer

This blog post was written by Wayde Beckman from the Health Sponsorship Council.

New Zealanders will have a new, easy-to-use tool that tells them when they need to protect their skin from the sun, with specific reference to where in the country they live. Using extensive research as well as audience and media feedback, the HSC has worked with the MetService and NIWA, in consultation with the Cancer Society, to produce a new UV radiation public communications tool – called the Sun Protection Alert to replace the UV Index.

The Sun Protection Alert will be the new UV tool used in New Zealand from November onwards and conveys simple information that’s specific to each area of the country for that day.

The new Sun Protection Alert graphic as displayed on metservice.com

 

The new approach to an old problem
Name: It’s called the Sun Protection Alert and tells you what to do when the sun is at its strongest.
Time: The Sun Protection Alert advises you of the actual time when you need to protect yourself from the sun. The time can change in 5-minute increments from one day to the next.
Simple: The Sun Protection Alert conveys simple information that is easy to understand and act on.
Relevant: Sun protection times indicate when the UV Index reaches 3 or above. The times and ultraviolet radiation levels will differ up and down the country as they are based mainly on latitude
Sun safety messages: Sun safety messages have been incorporated into the tool e.g. seek shade or reapply sunscreen. These messages will change regularly to maintain interest and in some cases will reflect the forecast weather e.g. if it’s a cool or cloudy day the sun safety message will be “Even on cloudy days” or “even on cooler days”.

Some things NZers ought to know…
The NZ lifestyle, the envy of many other countries, has given us the highest melanoma rates in the world – even higher than our mates across the ditch. In recent years, our melanoma death rates have been on a par with the NZ road toll.

Sunburn is a big concern because it is linked to melanoma, the most deadly form of skin cancer. Skin cancer is largely preventable by taking simple measures to protect ourselves from the sun.

Sun Protection Advice to use from September to April

For more information on Sun Protection go to http://www.sunsmart.org.nz

Rugby Weather: Fog

Rugby and fog do not go well together. Fortunately, in the days when rugby was played in the afternoon, they did not meet up much, except for the occasional test in Scotland when the All Blacks disappeared into the “gloom” as they scampered in a late try.

However, the introduction of night-time rugby gave fog a chance to get on the field for some game time. Especially in the United Kingdom, where evening games sometimes have to be cancelled when fog turns up.

In New Zealand, fog showed us what it could do when it rolled into Christchurch an hour before the kickoff of the Super 14 final between the Hurricanes and the Crusaders on 27 May 2006.

As a television spectacle the event was seriously compromised. The cameras down at ground level sometimes got a reasonable view but those high up were mostly obscured. Nicknamed “gorillas in the mist” the contest was won 19-12 by the Crusaders.

The Hurricanes, who do not have much fog of their own as it is usually too windy in Wellington, also got to suck up some Hamilton fog at the end of the Super 14 semi-final against the Chiefs in May 2009, which they also lost. Situated on a river, with swamps nearby, Hamilton is the most fog prone major city in New Zealand. After Hamilton, Christchurch is the next foggiest because it is close to the sea, so the air is often very humid.

Fog formation is helped when there are a lot of condensation nuclei in the air. Many of these come from tiny plants in the sea known as phytoplankton. When tiny animals, known as zooplankton, nibble phytoplankton the chemical dimethylsulfoniopropionate is released into the water. There it changes to dimethyl sulphide (DMS) which gets into the atmosphere when breaking waves throw small water droplets into the air, where they evaporate.

In the air, DMS changes to four different chemicals, three of which act as cloud condensation nuclei. DMS also helps make the characteristic smell of the air at the beach.

Fog: Photo copyright Pernell Hartly

Smoke particles can also act as condensation nuclei. Indeed, the celebratory fireworks after the Crusaders victory resulted in a temporary thickening of the fog in Christchurch. During the Napoleonic wars so much smoke was produced by the massed cannon-fire that fog would sometimes envelope the battle field giving rise to the term “the fog of battle”.

Before the clean air laws were enacted, smoke from coal fires and industry used to cause the famous pea-soup fog in London. In December 1952, a notorious fog lasting for days was blamed for 4000 fatalities, mostly from bronchitis and pneumonia. Breathing this particular fog actually caused pain as a portion of the 1000 tons of dirt particles suspended in the London air was sulphur dioxide which combined with water droplets and oxygen to form sulphuric acid.

Some playing-fields in Scotland have underground heating to prevent the soil freezing when frost strikes but there is not much you can do to prevent fog. During the Second World War a lot of effort went into discovering a way of clearing fog from airfields.

The only method that worked, and then only temporarily, was burning petrol sprayed from long pipes either side of the runway so that planes landed between walls of flame. But at nearly 30,000 litres of petrol per landing, it was prohibitively expensive.

Fog is just cloud resting on the ground, and clouds are often found resting on the mountains. So even before night rugby came to New Zealand there was one place where fog frequently turned up before game time and that was the coal mining settlement of Denniston, situated on a plateau 600 metres above sea-level on the South Island’s West Coast.

Although good for fog, Denniston was not a particularly good place for soil and grass. The rugby ground had been bulldozed out of rock and was covered in new load of sand brought up from the beach at the beginning of each season.

Rugby in the fog had certain disadvantages. A ball kicked high in the air, for example, would disappear and players have to wait around for the telltale thump to discover where it came back down.

There was, however, some home advantage. Visiting teams found playing in the persistent fog somewhat confusing, and if the game was going badly for the home team an extra player could be slipped on in the backline to stiffen the defence.

Nor was this astute use of local conditions restricted to the rugby team. An excellent soccer team from Millerton was once unable to make headway against Denniston until the fog lifted, revealing that Denniston had four extra players on the pitch.