Monsoon

The climate of the north west of Australia is governed by two seasons, "the wet" and "the dry". This annual cycle, as regular as a heartbeat, dictates the rhythm of life for plants and animals of this region.

The monsoon system that arrives with the wet, swings with the sun between Asia and Australia.

What is a Monsoon ?

A monsoon refers to a seasonal reversal of wind direction. In Northern Australia, south easterly trade winds characterise the dry season, and the wet or monsoon season is characterised by a north westerly monsoonal flow.

 

The Australian Dry Season ( April to November )

During the dry season the predominant wind direction is south easterly - the south east trade winds.

They're moderately cool and very dry in Australia's north west because they originate from the centre of the desert. This has the effect of pushing the monsoon system north into South East Asia and the Indian subcontinent.

The Indonesian Throughflow

The Indonesian throughflow runs from April to October. Water from the western Pacific Ocean flows down through the deeper gaps in the Indonesian Archipelago. Two of the main sites of throughflow are the Lombok Straights, between the islands of Bali and Lombok, and the gap between the island of Timor and Australia.

The Leeuwin current that flows down Australia's west coast is a warm tropical current that originates as an offshoot of the main throughflow that passes between Timor and Australia.

The throughflow dissipates vast amounts of heat energy from the waters of the western Pacific Ocean into the Indian Ocean. It has been estimated that at it's peak, throughflow transfers enough energy as heat to power a 100 watt electric lightbulb on every square metre of the Australian continent.

This vast energy transfer has the effect of lowering sea surface temperature to Australia's north, reducing the evaporation of water. This makes the air drier and so rainfall in the region to the south of the equator is greatly reduced.

In late September / early October above the Himalayas and Nepalese plateau, a region of high air pressure forms.

This system basically remains in place from October to March. Cold dry air descends blowing out to the south.

The regional air flow changes from the Southern moist monsoonal flow of the Indian monsoon, to a cold dry flow that marks the arrival of the dry or winter season in the Northern hemisphere.


It has been noted that there is a relationship between the depth of the snow that falls in the Himalayas and the amount of rainfall received in north western Australia.

In late October the throughflow from the Pacific to the Indian Ocean, to the north west of Australia, slows, stops and may even reverse at times as the Indian Ocean Counter Current flows west to east into the Timor gap and "blocks" the throughflow.

This leads to a large raft of relatively still water to the immediate north west of Australia. This body of water begins to heat under the tropical sun.

As the sea surface temperature rises, evaporation increases and moist air from this region, thought to be the source of humidity and moisture, will eventually fall during the Australian monsoon ( you only get monsoon systems where these static masses of water called warmpools form, not where the currents make the seas cool or cold ).

From late October to March the land mass from the Pilbara to Alice Springs in the red centre heats up as the suns path swings to the south with the change of seasons.

This vast area becomes extremely hot.

It takes several months for the landmass to finally reach its peak heat in December. This level is then suststained until late January or early February.

The very hot air close to the land surface rises, leaving a region of lowered air pressure ( as the air that was there has risen ), and a heat low is formed.

Heat lows only occur over large landmasses. Air flows in to fill this area of lower pressure ands help pull the monsoon south over the Australian continent.

During the wet season there are usually two or three major monsoon events. These events occur when the monsoon trough ( a low pressure trough associated with intense rainfall ) moves south over the landmass of north Western Australia.

The trough may remain over the land for periods of one day, to several weeks.

It usually overlies the continent for about seven days, during which time strong north westerly winds blow and rain falls almost constantly.

The later phases in February and March are often longer and more intense. It is then that the cumulative effect of the rains may be seen as surface water becomes evident.

This arrival of the monsoon trough occurs in intervals of about 40 days, and is thought to be connected with the arrival of the Kelvin wave - an easterly moving, globe circling, atmospheric wave, seen as a mass of increased cloud activity as it moves in from the west towards Australia.

The periods between the monsoon events are known as break phases.

In the Making

The Search for Whale Sharks

Filiming the whale sharks off Ningaloo Reef in Western Australia was a major problem. It was a bit like looking for a needle in a haystack.

Firstly, you needed to get the seasonal timing right - in our case it was the height of the season after the April full moon and associated coral spawn. This is when whale shark numbers have historically been at their highest off Ningaloo Reef.

Secondly, the search process is expensive. We needed to charter a 17 metre ocean yacht to live and work in, employ a crew of eight and keep a light plane aloft for hours at a time.

The search plane and pilot was coordinated by our highly experienced skipper, Peter Lake. He spent hours at a time looking for the whale sharks from up in the air.

A plane is the only practical way to find these giants of the deep and extends the search area to literally hundreds of square kilometres.

On the first full day at sea the plane found a whale shark. As we quickly learnt - experience and a touch of luck is the key to finding whale sharks - and we had a great boat and crew. We immediately altered course to intercept the shark. The two camera crews stood by.

The rules for filming and interactiing with whale sharks are very strict and are in place to protect them. A license and permit is required to operate a commercial whale shark operation. Only one boat at a time can enter the contact area for a limited period. These rules are enforced by the skipper of the boat and CALM and Parks Australia officers.

The plan was to drop one camera crew in the path of the shark and let the shark swim to them. The first drop was perfect and the shark swam straight up to the camera.

Although they looked as though they were moving slowly, it was almost impossible to keep up with the sharks underwater. The camera crew were wearing huge long fins for maximum speed but were soon left in the sharks wake and eventually lost contact.

We then dropped the second crew in the path of the shark and retrieved the first crew who had now surfaced. They were tired but elated - we had the first shot in the can.

The second camera crew didn't fare so well. They saw the shark but it turned away, dived and disappeared into the deep. As we picked them up our contact time expired so we left the area, satisfied that we were off to a good start.

But the satisfaction was short lived because we didn't see another whale shark for another eight days. We did however come across hundreds and hundreds of Bridal Veil jellyfish, moving up and down the water column. They were in the warm Leeuwin current slowly drifting south.

Initially the camera crews were worried about getting stung by their long tentacles but soon discovered they didn't sting.

We also came across a large school of Australian anchovy who were probably migrating to deep water from the shallows of Exmouth Gulf. The anchovy school was being hunted by tuna.

Our camera crew quickly entered the water and were soon caught up in the fray. The anchovy school was broken up by the tuna's constant attacks.

By this time we had begun to feel depressed about our hopes of finding Whale sharks.

After our first encouter we had not seen a single Whale shark despite hours of searching so we decided to extend the trip by one more day.

We sailed south on Peter the skipper's hunch and finally came the call we had all been waiting for.

The pilot had found a large whale shark, about three nautical miles to sea from where we were. We set sail and prepared to film.

Would the shark stay close to the surface? Would we get there in time? Nervous anticipation gripped the boat as we slowly drew closer. We spotted the shark still close to the surface and dropped a crew in its path. The shark kept going straight to where we dropped the crew.

It was finally happening after eight long days of waiting we had found a big whale shark. Then came another call from the plane, the pilot had found another shark and then another. The day became a blur of dropping off camera crews and picking them up again. We think that there may have been up to six sharks in the area.

We finally had the footage in the can. With great relief we set sail for home, sailing all night and arriving back at our mooring at dawn.

Filming the Baked Crocodile

We were told there was a large stranded crocodile in the Northern Territory's Kakadu National Park. Immediately we made arrangements to film it.

It was during November and the time of year year known as the build up - the transition from the dry season to the wet or monsoon season.


The temperature at this time is incredibly hot - 35+ celsius and very, very humid. The entire landscape is crying out for water. In some places there's been no rain for five months.

In the middle of a broad plain lies a sea of cracked mud. In its centre - a 2 metre Saltwater Crocodile. The sun is fierce and the air scorching.

The crocodile is motionless, its head buried under the damp earth. It's impossible to tell whether its alive or dead.

Finally, there is as slight movement of its flanks - at least we know that it's alive, if only just.

For the entire day the crocodile didn't move even though it must have sensed our presence as we moved about the area filming.

There were several aquatic file snakes also trapped in the mud. At regular intervals their heads would emerge from the mud to gasp a breath of air before disappearing again into the muck. They too were hanging on to life by a thread, waiting for rain to fall.

It was hard to believe that where we were standing was actually close to the centre of a billabong. In a few short weeks after the rains arrive, water would again fill this pool.

Where the Crocodile was lying in the mud, would eventually be covered by 2 metres of water. If he survived until the rains arrived he would rule this domain. Aquatic plants and lillies would emerge from bulbs and tubers buried in the dry cracked mud. The file snake will be freed from their mud prison.

It is still a matter of great amazement that this country can swing from such extremes of wet and dry. It is the seasonal change of the global monsoon system that dictates life right across the north west of Australia.

Merten's Magic

We discoverd Merten quite by accident while we were on a reconnoitre trip looking for a set of waterfalls to film in flood during the monsoon rains.


This large lizard was just basking in the sun on a rock. As we approached it moved off the rock and slid into the stream. Fascinated, I watched as it proceeded to hunt then catch a fish from under a rock. It surfaced and then swam to the opposite bank.

This was my first close encounter with a Mertens Water Monitor. I was amazed that here was an animal that I had not seen on film before. The location was perfect, the water was crystal clear and the fish it was feeding on appeared to be abundant.

Here was a lizard dependent on the monsoon season to keep its stream flowing and healthy.

We began by filming Merten on land. The lizard slowly became more familiar and less concerned about our presence and we were able to get to know it better.

We worked out where its territory began and finished, when it hunted, how it hunted, and how it interacted with other Water monitors up and down the stream. We noted that it was eating mainly Purple Spotted Gudgeon, that hid in crevices and under rocks. We also noted that if it caught a Gudgeon from under a rock, another Gudgeon would move in and take up residence almost immediately.

Before to trying to film underwater we got into the stream with the monitor to see how it would respond. After some initial wariness we were delighted to find that we were being ignored. Merten just went about its business in the same way as we had seen from shore.

To film underwater we needed to use a film camera in an underwater housing. The water was only about 1.5 metres deep so it was possible to film with mask and snorkel only. The water was crystal clear and you could see for the length of the pool.

Over about five days we worked in the water with Merten. Much of its day was spent out on a rock sunning or patrolling its territory.

We were lucky enough to film a confrontation underwater between Merten and his neighbour.

To film Merten catching a fish was just a matter of waiting close to its favourite spots. Merten only caught two fish a day on average.

Finally we were finished and the shots we needed were in the can. We had film of this remarkable animal fighting and feeding underwater. It really is a honour when a remarkable animal like this lets you film its daily life.

Lightning

One of the most outstanding features of the monsoonal north west of Australia, during the wet season, is the frequent and spectacular thunderstorms.


These lightning shows are like nature's firework displays, and to me illustrate the enormous amounts of energy in the atmosphere during the dynamic Monsoon season.

The lightning in Monsoon was shot over the entire life of the program. We kept an eye out for thunderstorms every night that we we were on location.

At the beginning of production I had a desire to better my previous efforts in recording images of lightning. I had filmed lightning in the past for two programs, The Big Wet and Rhythms of Life but this time I really wanted to film exposed lightning bolts and lightning during the day - something that I had not been able to successfully do in the past.

With this in mind I became an obsessive storm chaser - every day and night I'd be out there watching, waiting, filming - trying to get the perfect shot.

How we Filmed Lightning

If you're shooting stills images of lightning you're often trying to get just one great frame or so out of a storm. But when you're filming lightning you need to get a continuous shot that lasts as long as possible. Ten seconds is ideal.

To do this we used a time-lapse camera where the film was exposed slowly one frame at a time. This had the effect of condensing time so that a shot that lasts ten seconds on television may have actually taken several hours to film in the field. With this technique you're trying to get one good bolt of lightning on every frame of film, if possible.

The ideal storm for filming is one that is very active - at least four bright lightning flashes per minute, slow moving and lasting for several hours. This rarely happened, but when it did we were out there and ready.

The other key to filming lightning is where to position the equipment and where to point the camera. This sounds quite simple but it's in fact the hardest part of the process. If it takes up to four hours to film the shot then the storm must remain in the frame for all that time. Sometimes it would change track and leave the frame or collapse and peter out. It could also roll over the top of the camera.

Most of the lightning for the program was filmed in the Darwin region. This was mainly due to the network of roads that enabled freedom of movement to position the camera in the best possible location. It was not uncommon for us to travel up to 400 kilometres in a single night storm chasing.

Mammals

Agile Wallaby

Agile Wallabies inhabit the the coastal plains, floodplains and woodlands right across tropical northern Australia.

They are the most common macropod in the tropical coastal regions.

They live in small social groups and can often seen feeding out in the open, on the margins of woodlands and floodplains just before dusk.

As the plains are inundated during the monsoon season they move to dryer and higher ground in the woodlands.

Common Planigale

Planigales are the smallest carnivorous marsupials in the world. For their tiny size (4 -10 grams), they are incredibly aggressive, talented and able hunters.

With a formidable array of sharp teeth, they will take on and kill prey their own size. They eat insects and larvae, small lizards and young mammals.

During the dry season they often live in cracks in the ground on the tropical plains. In the wet season they seek refuge on higher ground or in trees and shrubs, finding a living stalking and eating stranded insects.

Common Wallaroo

Australia's most common Macropod, the Euro, is an adaptable survivor. Their range extends over much of the continent.

They can live with very little access to free water and will even excavate wells to find a drink.

During the heat of the day they often shelter from the fierce desert sun inside caves on breakaways and rocky hillsides. They can often be observed at dusk when they emerge to graze and drink.

Dusky Rat

Dusky rats are an integral part the ecology of the monsoonal floodplain of the Northern Territory of Australia.

They feed on seeds and underground corms.

During the wet season, when the plains are inundated, they move to higher ground. At this time many die from drowning, stress or starvation. In the dry season, those that survive breed very rapidly and numbers again rise to very high population densities. They are a very important food source for the Water Python - their main predator.

Orangoutang

Orangoutangs live in the equatorial rainforests of South East Asia. Their main strongholds are in the rainforests of Borneo and Sumatra.

They are thought to be essentially solitary in habit. The young are highly dependent on their mothers for about two years and will then often stay in the vicinity of their mother for another year or so.

Much of their behavior is apparently learnt by observation and experimentation under the watchful eyes of Mum.

Red Kangaroo

The largest of Australia's Macropods is the majestic Red Kangaroo. They live in the arid regions of Australia where average annual rainfall is less than 500 mm.

During the heat of the day they are most often seen lying in the shade under trees and bushes.

If they get too hot, they will lick saliva onto their forelimbs where blood vessels lie very close to the surface. As the saliva evaporates it cools the skin and blood in a process akin to sweating in man.

Yak

Yaks are vital to the Nepalese people. They provide transportation over the high alpine passes and along the narrow mountain paths.

Domesticated Yaks are often cross breed with cattle. These animals are often quieter than Yaks for pack work.

Yak herders move to lower altitudes as the Indian Monsoon season departs and the High meadows begin to chill with the arrival of winter.

Reptiles

File Snake

This File Snake was one of several stranded with a large saltwater crocodile in a mud hole.

The mud hole was all that remained at the end of the Dry season of what was a substantial billabong during the Wet.

File snakes are common residents in billabongs and rivers across northern Australia. They eat mainly fish and are themselves in turn eaten by crocodiles and Jabiru.

Merten Water Monitor

Mertens Water Monitor is found along small streams and creeks in the tropical north of Australia.

This lizard is equally at home on land or in water. They are most often seen sunning on an exposed rock or log close to water. When disturbed they quickly disappear into the water.

In the Wet season their main diet appears to be fish caught while diving underwater. They a superb swimmers and can hold their breath for several minutes at a time. During the dry season their streams may stop flowing or dry up. In this case they become totally terrestrial until the wet season returns and replenishes their favourite pools.

Like most monitors they are opportunists when it comes to food, taking carrion, birds, eggs and insects if there are no fish available.

Ring-Tailed Dragon

In the heat of the fiery Pilbara, a male Ring Tailed Dragon lives on the horns of a dilemma.


Life is a constant juggling act. To maintain his territory he must be constantly vigilant for rival males. To do this, nothing beats the view from the top of a high rock.

The problem is, that under the fierce sun the rock is hot enough to fry an egg. His solution is a quick dash to the top, sitting with toes raised off the hot rock to stop them burning. He scans his territorial domain and quickly makes a dash for the cool shade.

Saltwater Crocodile

The Saltwater Crocodile is one of my favorite creatures. You cannot help but admire its amazing ability to survive.

Historically it was hunted agressively - some say it came close to local extinction. But since protection its thrived.

Numbers have again built up to the point where they are easilly seen in the rivers and billabongs of the Top End.

The most important thing to remember about crocodiles is that they are the only animal in Australia that have the potential to look upon humans as a source of food.

Warning signs are there for good reason so don't ignore them. Always remember crocodiles can be dangerous but they are a vital part of the tropical ecosystem.

Birds

Double-barred Finch

Double-barred finches like Spinifex Pigeons are seed eaters and are very dependent on water to digest their diet of seeds.

They are often seen in social flocks of up to about 30 birds, either hopping on the ground, picking up fallen seeds or roosting together on low branches.

Orange-Footed Scrubfowl

Orange-footed Scrubfowl inhabit the moist monsoon vine thickets of the Kimberley and Top End.

They build large mounds of leaves and vegatation where their eggs are incubated.

After the first rains of the Wet season, their nest mound starts to heat up. It is activated as microbes begin to break down the organic material. Eggs are laid deep inside the mound when the temperature is right.

Jabiru

The Jabiru nests high in tree tops during the dry season (April to November) in Australia's north.

They are very wary around the nest, making them very hard to observe and film.

Rainbow Pitta

The Rainbow Pitta is normally a very shy bird. During the dry season they are almost invisible in the monsoon forest thickets of the Northern Territory's Top End.

With the first rise of humidity at the onset of the monsoon season they become very active.

Spinifex pigeon

Spinifex Pigeons are permanent residents of the arid regions of Australia's north west.

As seed eaters they are dependent on waterholes recharged by wet season monsoonal rains and showers.

As the dry season progresses they concentrate around the ever decreasing water sources.

Tawny Frogmouth

This Tawny Frogmouth was found sitting beside the road during a monsoonal downpour.

It just sat wet and miserable on its perch, over a period of two hours where the rain did not slacken once I slowly edged closer and closer. It was totally unconcerned the camera about and me.

Tibetan Snow Cock

These birds migrate up and down in altitude following the seasons.

During the Indian monsoon season they climb up to higher altitudes.

At the end of the monsoon, as the weather cools in the northern hemisphere, they move down, forming large flocks at lower altitudes to feed and seek mates. Their frequent calls sound a lot like distant yapping dogs.

Whiskered Turn

Whiskered terns are very nomadic.

They are often seen feeding over the rivers and floodplains of the Top End of the Northern Territory. They usually hunt small fish in the streams of the plains.

During seasonal inundation of the plains they change diet to feed on stranded insects and grasshoppers.

White Plumed Honey-Eater

The White Plummed Honeyeaters move to the desert regions from southern Australia to take advantage of the abundant food associated with flowering plants in the northern desert regions after rainfall.

The Sturts Desert Pea is dependant on birds like the White-plumed Honeyeater for pollination. As the bird presses its bill into the flower to obtain nectar, pollen is deposited on the birds feathers to be transported to the next plant.

Fish

Australian Anchovy

Australian Anchovy migrate from shallow coastal estuaries like Exmouth Gulf out into the Indian ocean.

In autumn, as the warm Leeuwin Current pushes south, they depart from inshore waters and move out to the deeper Indian ocean.

This school was intercepted by tuna and formed a tight defensive ball. An individual is thought to be safer inside the dense crowd rather than out on its own.

Bridal Veil Jellyfish

Bridal Veil Jellyfish are ocean drifters. They move up and down the water column from the bottom to the surface with tentacles extended searching for microscopic food.

They were observed riding the warm Leeuwin current slowly moving southward.

Whale Shark

Whale Sharks arrive seasonally off Ningaloo reef in Western Australia.

They appear in March or April with the arrival of the warm tropical Leeuwin Current and at about the same time as the Corals Spawn.

It is thought that they may migrate down from the North either from the seas around Indonesia or the Philippines. For more images and information about Whale Sharks visit the Search for Whale Sharks.

 

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© 2000 Australian Broadcasting Corporation