Global Atmospheric Circulation- An Introduction

Atmospheric circulation is the large-scale movement of air by which heat is distributed on the surface of the Earth. Solar energy powers the atmospheric system and the energy circulations within it. The amount of solar energy (heat budget) received varies with latitude.  The tropics have an energy surplus as they gain more from insolation than is lost by radiation.  But the higher temperate and polar latitudes have an energy deficiency losing more by radiation than is gained by insolation

This disparity in the earth’s heat budget is counteracted by the ocean currents which accounts for 40% of the redistribution and atmospheric circulation accounting for 60% respectively.

This is achieved through three main convection cells:

1) Hadley Cell (Tropical Cell) 

2) Ferrel Cell (Mid-latitude Cell)

3) Polar Cell

While the Hadley, Ferrel, and Polar cells are major players in global heat transport, they do not act alone. Disparities in temperature also drive a set of longitudinal circulation cells, and the overall atmospheric motion is known as the zonal overturning circulation.
 
As the Coriolis force runs across the 3 convection cells it causes the deflection of the wind creating some main patterns:

1) Easterlies
2) Doldrums
3) Westerlies
4) Horse Latitudes
5) Polar Easterlies
6) Polar front

This post is going to focus on the Hadley cell as this is said to have most impact on the atmospheric circulation.

The Hadley cell is a three dimensional atmospheric circulation cell located at roughly 0 to 30° North and South of the equator. Low latitude air moves towards the Equator and heats up.  As it heats it rises vertically and moves polewards in the upper atmosphere. This forms a convection cell that dominates tropical and sub-tropical climates.

As mentioned previously in this post near the poles, heat is lost to space by radiation exceeds the heat gained from sunlight, so air near the poles is losing heat. Conversely, heat gained from sunlight near the equator exceeds heat losses, so air near the equator is gaining heat. Air rises near the equator, flows north and south away from the equator at high altitudes, sinks near the poles, and flows back along the surface from both poles to the equator.

The combination of these two processes sets up a general circulation pattern: air rises near the equator, flows north and south away from the equator at high altitudes, sinks near the poles, and flows back along the surface from both poles to the equator. The video above just demonstrates the Hadley cell circulation in more detail and summaries all of the above.

http://www.youtube.com/watch?v=DHrapzHPCSA

Classroom task

I would like to do a summary of the Hadley cell circulation. I would like the students to chose how they would do this but the requirements would include at least 6 bullet points of how the circulation works. Other tasks could include true/false statements about the Hadley cell also getting in the diagram and filling in the stages of the circulation cell.

Next post will be explaining the other two cells; Polar and Ferrel in more detail and also beginning to explain the major wind patterns.

Hurricane Irene August 2011

Hurricane Irene

Although I have already covered Hurricanes I thought it was only appropriate to do a quick blog post on the recent Hurricane to hit the shores of the Carribean and the southern states of the USA. Despite it being much less destructive than anticipated, the scale of damage caused by Hurricane Irene was still substantial.

Just a short video footage of the hurricane...

http://www.youtube.com/watch?v=CdW8vdUm70M&feature=related

Characteristics of Irene:

• The first notable Hurricane of the Atlantic season
• Formed on 20^th August and raged across the Caribbean, USA and up through Canada until dissipating on the 29^th August
• Highest winds recorded were 120mph and at its largest had a diameter of over    500  miles!
• At its peak Irene was a Category 3 Hurricane

Below is an image of the path Hurricane Irene took over the 9 days it was present over the Atlantic area. The image also shows when it was at its most dangerous using the Saffir- Simpson scale

3 p’s

Something I still remember from studying weather is the 3 p’s associated with natural disasters. They can vary by definition but im choosing Prediction, Prevention and Preparation. This is something that this article will focus on and will show how implementing the 3 p’s successfully can drastically reduce damage.

Prediction

The majority of this is done by the monitoring of Satellites and local weather conditions to determine the path the Hurricane is likely to take. By predicting this prevention methods can be put in place. Weather stations are constantly monitoring weather conditions so can issue warnings in advance to whether a tropical cyclone is likely to be upgraded to a Hurricane

Prevention

This particular category is hard to apply to Hurricanes as in the simplest of terms they are impossible to prevent. However, prevention can be applied in other ways including prevention of damage to housing, infrastructures and loss of human life. This is where Preparation is key as by putting solid methods in place prior to the Hurricane reaching shore the damage can be drastically reduced.

Preparation

Below are just some of the methods the USA had in place prior to the Hurricane reaching major cities such as New York:

• Severe Weather warnings in place across 8 states
• 2 million people ordered to evacuate including 300,000 people living in low lying areas of New York
• 90 shelters set up in New York for over 70,000 people
• Entire shutdown of New Yorks transit system including the subway, rail travel and bus travel
• 200 trucks of emergency supplies and 100,000 national guards on stand by 

What was the damage from the Hurricane? 

• 55 fatalaties caused by Hurricane Irene
• Total damage caused is approximately $10 Billion
• Extensive flooding across New york and Vermont

Conclusion

Although I haven’t covered any new concepts in this post it is always interesting to see how natural occurring events such as Hurricanes affect humans and how despite our technological advances we can’t overcome human nature. Despite this it is clear to see how our technology has allowed huge advances in predicting paths hurricanes may take and through this enabling preparations to be put in place such as mass evacuations and protections of infrastructure.

Finally, with the Atlantic Hurricane season only just beginning i think we can be fairly certain that more damage from Hurricanes will be felt over the coming months

Have a quick look at the below article which gives an interesting read....

http://news.bbc.co.uk/weather/hi/news/newsid_9504000/9504306.stm 

Measuring and Analysis of Climate- Some examples

Weather Balloons:

Weather balloons were first used over a century ago and were used to establish the presence of the stratosphere and tropopause. This equipment consists of a latex balloon, a parachute and a radiosonde which hangs below.

Similarly to the weather station, the radiosonde measures temperature with a thermometer, humidity with hygrometer and air pressure with a barometer, taking continuous measurements as the balloon rises. The equipment includes a tracking device which monitors the movement and converts wind speed and wind direction. An example of a weather balloon which climbed to 93,000 feet can be viewed here;

http://www.youtube.com/watch?v=dRZJdJ-HZY8.  

Satellites:

Infra-red satellite images play a large part in determining global weather patterns and revolutionized meteorology (the study of weather) in 1960 when the first image returned to earth. The image below shows infra-red radiation over the UK. This is emitted by both clouds and the earth’s surface and gives an accurate reading of temperature. This is found using a grey scale with lighter areas of cloud indicating where the cloud tops are cooler and therefore where weather features like fronts and shower clouds are.

This has come on a long way since the first satellite image, taken in 1960. This was the beginning of the highly accurate reports produced in the modern day.

Analyses:

The data provided by weather stations, buoys, balloons and satellite imagery are all compiled into highly complex mathematical computer models. The outputs of these are the weather forecasts which are produced and shown in the media every day.

A weather forecast is produced by translating physical laws which govern weather into mathematical equations. These equations form a 3D ‘dynamical model’, an example of which can be seen below (depicting Hurricane Floyd). The information which can be input into these equations is found using the measurement methods mentioned before.

These computer models forecast how the atmosphere is most likely to react over a period of time but are constrained by technology. For example certain variables may not be considered if they aren’t input. The forecast at this stage then needs to be translated into a more universal forecast using Model Output Statistics (MOS) equations. These are calculations which look at past model outputs and actual weather. By including actual weather this helps to provide a more accurate and localised forecast. A human forecaster will calculate the MOS equations and make a comparison with the computer model. This can then be used to make an accurate expectation of the weather.

Measuring and Analysis of climate

Moaning about the weather....very British but how easy is it to put together a weather forecast and is it done in modern times as it was done in the past. I have looked into the factors that need to be considered when discussing the climate and some ways climate is measured.

To measure climate accurately 7 factors need to be considered. These are:

·         Temperature and precipitation – varying temperature is arguably the most direct indication of changes within the atmosphere.

·         Pressure – similarly to temperature this is an indication of atmospheric conditions.

·         Biomass – this is analysed by monitoring flora and fauna over longer periods of time and identifying differences in species and mass.

·         Sea level – changes in sea level can indicate variations in ocean salinity, a factor known to both be greatly affected by climate and to greatly affect climate.

·         Solar activity – influences climate through varying solar radiation.

·         Volcanic eruptions – alter climate patterns locally by aerosol emissions.

·         Chemical composition – research indicates a strong correlation between certain gasses (e.g. CO₂ and CH₄) and temperature.

In the past measuring climate focused on air pressure, temperature, precipitation. This relied on comparatively simple technology such as the pressure gauge, thermometer or rain gauge. In the modern day, measurement and analyses of weather is primarily carried out using a combination of weather balloons, satellites and local weather stations.

Local weather stations:

Weather stations are able to measure several of the variables mentioned above using incredibly precise equipment. A weather station will typically be located in open areas where the human impact on surrounding environment is limited. Weather stations aren’t limited to set points on land but also come in the form of ships and buoys which can monitor conditions at sea.

Weather stations tend to have vast amounts of equipment to monitor wind speed, humidity and temperature which are measured with varying instruments.

Wind speed: most weather stations will be equipped with a highly accurate weather vane to indicate wind directions as well as an anemometer.  The anemometer indicates wind speed and is composed of small cups which are caught in the wind causing the device to spin at a speed. This spinning is then translated into a wind speed, commonly expressed in Mph.

Humidity: this is measured using a hygrometer. Arguably the most accurate type is the chilled mirror hygrometer which measures the temperature of a mirror at the point that a drop of moisture begins to condense. This gives name to the dew point.

Temperature:  the majority of weather stations are equipped with a ‘Stevenson screen’ which ensures the measurement of temperature (via a thermometer installed internally) isn’t affected by solar irradiation.

 The slats on the side allow air to circulate and ensure an accurate temperature reading. Two thermometers are placed inside, one of which is constantly wet. This can be used to indicate evaporation and (therefore humidity) in a similar fashion to the hygrometer.   

Next post- I will be adding some more examples of measuring climate and providing some form of analysis on the different methods chosen to monitor climate

Atmospheric Lapse Rates

What does it mean?

The atmospheric lapse rate describes the reduction, or lapse of air temperature that takes place with increasing altitude. Lapse rates related to changes in altitude can also be developed for other properties of the atmosphere.
There are three types of lapse rates, Dry Adiabatic, Saturated Adiabatic and Environmental Lapse rates.

If a material changes its physical state (that is, if its pressure, volume, or temperature change) without any heat being either added to it or withdrawn from it, the change is said to be adiabatic. So, an Environmental Lapse rates refers to a change in a physical state with heat added.

What affect do Lapse rates have on the environment?

The average atmospheric lapse rate results in a temperature decrease of 3.5°F (1.94°C) per 1,000 feet (304 m) of altitude.

There are two types of lapse rates, Dry Adiabatic and Saturated Adiabatic both of which have varying temperature changes, so what are they?

Dry Adiabatic - A dry, not saturated parcel of air, has a dry adiabatic lapse rate of 1°C/100m

Saturated Adiabatic - This saturated parcel of air has a saturated adiabatic lapse rate of 0.6°C/100 m

From the atmospheric lapse rates you can tell whether the atmosphere is stable or unstable. This can be seen when the actual lapse rate is either greater or less than the dry adiabatic lapse rate. This variation from the dry adiabatic lapse rate is what determines whether the air is stable or unstable.

The vertical air temperature distribution in the atmosphere is highly variable. For dry air it ranges as follows:

1. Very stable : Temperature increases with increase in altitude. This is a "plus" temperature lapse rate, or an inversion.
2. Stable : Temperature lapse rate is less than the dry adiabatic rate, but temperature decreases with altitude increase.
3. Neutral : Temperature lapse rate is the same as the dry adiabatic rate of 5.5 degrees Fahrenheit per 1000 feet increase.
4. Unstable : Temperature lapse rate is greater than the dry adiabatic rate. It may be 6 degrees Fahrenheit or more.
5. Very unstable : Temperature lapse rate is much greater than the dry adiabatic rate, and is called super-adiabatic.

Classroom tasks:

Some tasks could include picking key words and asking for explanations. I would want students to know the main difference between lapse rates and also explain each condition for the stability of the atmosphere.

Although this isnt the best example, there could be a graph plotting exercise showing lapse rates and temperatures:

http://www.mhartman-wx.com/fcst_tools/lapse_rates.html

Human Impact- Case Study 1 - The Great Pacific Garbage Patch

Each year, three times as much rubbish is dumped into the world's oceans as the weight of fish caught.

So what is the Great Pacific Garbage Patch...

It is a gyre of Marine litter twice the size of France situated off the coast of California that is estimated to contain 100 million tonnes of waste, predominantly plastic. In 2009 the ocean was said to have 46,000 pieces of plastic per squre kilometre of ocean which out weighs the amount of Plankton by the ratio 6:1.The great Pacific patch is the largest landfill site in the world although there are other Garbage patches, most notably in the North Atlantic and the Indian Ocean.

How did it get there?

The plastic has travelled far and wide down streams and rivers finally entering the ocean where the waste accumuates into one large landfill site. Additional to land pollution of plastic, other sources include commercial fishing, recreational boaters, merchant military vessells and offshore oil and gas platforms.

 http://news.discovery.com/videos/earth-whats-an-ocean-garbage-patch.html

What are the main affects on the environment?

The largest effect of the garbage patches in the ocean is to the marine life. Although it is widely accepted that plastic itself is not toxic, it attracts and allows other harmful chemicals to accumulate such as PCB and DDT. These chemicals in high levels are dangerous to most species of animals.

"Worldwide, according to the United Nations Environment Programme, plastic is killing a million seabirds a year, and 100,000 marine mammals and turtles."

Although chemical pollutants are dangerous the main cause of death is entanglement in the plastic waste or swallowing and thus choking on plastic particles. The larger pieces of plastic can cause the entanglement however it is the smaller pieces which can be swallowed. Plastic is not biodegradable however, it can be photodegraded. This breaks down larger pieces of plastic in smaller particles which then remain in the ocean.

What can be done to help?

There are many ongoing relief efforts which are aimed at recovering large amounts of plastic from the oceans. There are also quite a few charities which are commited to helping clean up the garbage patches.

One charity which appears quite influential from the research i have carried out is http://www.5gyres.org/

The main mission of the charity is outlined below:

"To conduct research and communicate about the global impact of plastic pollution in the world’s oceans and employ strategies to eliminate the accumulation of plastic pollution in the 5 subtropical gyres."

This is just a small example of how humans can impact the environment on a grand scale with the consequences of human actions irrevocable.  Although this does stray away from the topic of weather slightly i do think its important to look at this topic in broad terms.

Classroom tasks
This is a difficult issue to tackle with the human race so accustomed to using plastic as the predominant packaging material. One task could students working together in groups to think of ways the "garbage patch" phenomena can be avoided in the future and also how best to tackle the current issue of waste in the oceans.

Another question to pose could be whether they think its acceptable to use to oceans in such a way. This could be a good linking question as can be made relevent to alot of geographical concepts such as space, place and population  

Ocean currents

A Current is the motion of water. The currents in the ocean can be divided into two main types. The upper km of the ocean is governed by the wind whereas the deeper parts of the ocean are affected by mixing of deeper currents to create water with varying density.

Surface currents:

They make up 10% of all the oceans water and is controlled by the wind. The surface currents are dominated by Gyres. So what are Gyres.....

Gyres are, in the simplest of terms, a large system of rotating ocean currents. They are caused by the wind blowing on the water pushing it in a direction. When the coriolis force pushes against the wind direction gyres form from this rotational pattern.

There are 5 major Gyres:

Indian Ocean Gyre

North Atlantic Gyre

North Pacific Gyre

South Atlantic Gyre

South Pacific Gyre

All of the major gyres can be seen in the map above. A lot of the research i have done on this topic has unearthed a large quantity of environmental studies in ocean pollution. The predominat topic are the major garbage patches which have formed in the oceans, this will be covered in my next blog post.


Deep Ocean currents:

These ocean currents make up 90% of the oceans water and mainly determined by water density.

The Thermohaline Circulation

This is a density driven current which involves an overturning of water to create different density pockets with varying temperaratures. This circulation moves warm water polewards where it is then converted into cold water which sinks and flows down towards the equator.

The two main interconnected processes are:

1) Deep convection
2) Upwelling through the rest of the ocean to bring the cold water back to the surface

Why is the conveyor belt so important?

The Thermohaline circulation has a major impact on the global climate. The circulation is the main supplier of heat to the polar regions and thus controls the levels of ice in this area. This is so vital as any slight changes in global temperatures are known to have a dramatic effect on sea levels rising due to melting areas of ice.

Although it is not known for certain the level the THC affects global climate, it is believed to affect the radiation budget and alongside this largely influence levels of carbon dioxide in the atmosphere.

This falls into the climate change category which i will focus on in some of my later blogs. I will look specifically at how changes in climate effect certain weather patterns such as Hurricanes and Ocean currents.

Tasks for the classroom:

This was a difficult one as although i find the oceans quite enthralling due to the vast size of them and their influence on the world trying to find exciting tasks which will enhance learning has not been easy. As my next topic about the oceans is about the shutdown of the THC i might set them a task to research the effects of this might be on the world.

Random facts:

- 90% of all volcanic activity occurs in the oceans.
- The speed of sound in water is 1,435 m/sec - nearly five times faster than the speed of sound in air.
- Less than 10% of our oceans have been explored by humans
- Mt Everest is more than 1 mile shorter than the deepest part of the ocean. Challenger Deep is 6.86 miles deep.