#itcz

Africa’s worst drought caused by air pollution

In a scientific sense, the word “aerosol” means tiny particles dispersed in a gas. Most people probably know the term from aerosol spray cans, where it is much more commonly used; the term fits because the can is spraying out very fine, aerosolized particles into the air.

That definition is important to this post on the Sahel region of Africa which has suffered recurring droughts for decades. This photo shows a goat killed during one of the many drought periods that have hit the nation of Ethopia, part of the Sahel region that sits to the south of the Sahara desert. These droughts have been an issue for decades; for a cultural reference, the deaths from these droughts drove the “Live Aid” charity concerts and associated music releases during the 1980s.

A new paper published this summer in the journal Geophysical Research Letters proposes that the direct cause of these droughts is aerosol air pollution from the developed world.

Aerosol particles can impact global climate. The most common aerosol particle formed from air pollution is a sulfate aerosol; a small droplet of sulfuric acid formed from sulfur released into the atmosphere. Sulfate aerosols are thought to have a cooling effect on the climate; when they get into the upper atmosphere, they reflect some amount of sunlight and may also help form clouds.

Prior to the establishment of environmental regulations in the 1960s and 1970s, the developed nations in North America and Europe were pumping out large amounts of sulfate aerosols into the atmosphere by burning fossil fuels. One consequence of these particles was that global temperatures didn’t rise very much during the 1960s; the aerosol release was enough to offset the warming from CO2 increases.

This cooling effect was strongest over North America and Europe because that is where the aerosols were concentrated. This new study, led by researchers at the University of Washington, took a more detailed look at the results of this localized effect.

One of the rainiest places on Earth is a location close to the equator known as the inter-tropical convergence zone (ITCZ). Air from both north and south converges in this region and rises, leading to consistent rainfall; many rainforests such as the Amazon basin are formed because of this geographic feature.

These researchers found that normally, the location of the ITCZ varies slightly due to ocean currents, but in the 1960s, it began consistently migrating south. The Sahel region sits just north of the ITCZ, and this movement pushed the rain-band away from the Sahel region, taking away the rain that would occasionally reach this arid zone.

At the same time, lakes in northern Brazil and in central Africa began receiving even more rain; the areas on the southern edge of the ITCZ got the rain that used to go to the Sahel.

This migration of the ITCZ directly correlated with the increasing release of aerosols in the northern hemisphere, suggesting a connection. To strengthen that argument, the researchers tested dozens of different climate models and found the exact same result each time; aerosol-driven cooling in the northern hemisphere pushes the ITCZ south.

Since the 1990s, North America and Europe have cleaned some of their emissions, the ITCZ rain bands have migrated somewhat back to the north, and although droughts still continue in the Sahel region, they are not as consistent as the drought at the peak of aerosol emissions.

There are a number of implications of this research. First, just from a human perspective, it’s scary to think that the coal plants in the West are killing people in Africa through dehydration and starvation. Second, China has taken over as the main producer of aerosols over the last few years, and its air pollution may drive similar climate shifts in other areas of the world (the researchers are now attempting to understand exactly these impacts).

Finally, releasing sulfate aerosols into the atmosphere keeps being proposed as a way to “geoengineer” our way out of the climate change problem; since they have a cooling effect they could offset the warming (see this recent TES post: https://www.facebook.com/TheEarthStory/posts/544004955660553). But, this study should serve as an important reminder; sulfate aerosols don’t just cause cooling, they’re not just “anti-CO2”, their release can shift regional and global weather patterns in unpredictable ways.

-JBB

Image credit: Andrew Heavens, shared under creative commons license http://www.flickr.com/photos/andrewheavens/100048522/

Original paper (Subscription): http://onlinelibrary.wiley.com/doi/10.1002/grl.50502/full

Press report: http://news.yahoo.com/africas-worst-drought-tied-wests-pollution-164423549.html

आईएमडी के मुताबिक, मानसून के 22-23 जून तक दिल्ली पहुंचने की संभावना है

दिल्लीवासियों के लिए कुछ अच्छी खबरें, भारत का मौसम विभाग बुधवार को कहा कि मानसून 27 जून की सामान्य तारीख से तीन से चार दिन पहले राष्ट्रीय राजधानी में पहुंचने की संभावना है। कुलदीप श्रीवास्तव, आईएमडी के क्षेत्रीय पूर्वानुमान केंद्र के प्रमुख, ने कहा कि पश्चिम बंगाल और पड़ोस में एक चक्रवाती संचलन 19 जून और 20 जून तक दक्षिण-पश्चिम उत्तर प्रदेश की ओर बढ़ेगा।

उन्होंने कहा, “यह 22 जून से 24 जून के…

What it is and its role in Trinidad and Tobago Rainfall

25/06/2018

Pictured above: a hyperactive and prolonged ITCZ in October 2017

The Inter Tropical Convergence Zone or ITCZ as it is commonly called is one of the main climatological features of the global atmosphere. 

It is a zone (belt) of low atmospheric pressure that forms where the northeast trade winds meet the southeast trade winds (zone of convergence) near the earth's real equator. 

When the two trade wind regimes meet, moist warm air is forced upward. This causes water vapour to condense as the air cools and rises, resulting in the formation of a band of clouds with heavy rainfall. 

Photo credit: http://principiojoanne2196.blogspot.com/2012/06/intertropical-conversion-zone-itcz.html

The location of the ITCZ varies throughout the year and dramatically affects rainfall in areas where it is located.

It is also called the thermal or climate equator because the zone of low pressure associated with the ITCZ migrates with the changing position of the thermal equator. 

The thermal equator is that zone that receives the most intense heat from the sun and hence moves with the movement of the sun. The ITCZ, therefore, appears to move north and south with the overhead sun, because where the sun is overhead is likely to be the hottest area. 

As such, the movement of the thermal equator shifts the belts of planetary winds and low pressure zone to the north and to the south annually.

When it moves north over Trinidad and Tobago it brings wet weather and significant rainfall, with thunderstorms regularly occurring directly within the associated band of cloud mass. Land areas heat up a lot more quickly than the sea so you will find that the ITCZ is particularly active over land areas during the day and more active over coastal and sea areas during the night.

Trinidad received around 1643 mm of rainfall per wet season.

Trinidad has a twin-peak rainfall regime, with a major peak in June-July-August and a smaller peak in November as the graph above shows for Piarco, Trinidad. 

This twin peak in rainfall occurs because the ITCZ moves northward in the early part of the wet season, which brings much rainfall with it, As it moves southward-- as the sun migrates later in the season-- it brings another peak in the rainfall totals. 

Tobago has average rainfall totals per wet season of around 1250 mm and, as the graph below shows, Crown Point in Tobago receives an early peak in rainfall in July when the ITCZ is furthest north and its main peak in November when the ITCZ is on its way southward. 

It is important to note that the ITCZ is not the only feature affecting rainfall during the wet season.

Usually, the wet season accounts for 75 to 80% of the annual rainfall total in Trinidad and Tobago. 

Grography – ITCZ, Doldrums, Horse Latitude

Doldrums:- At sea, ITCZ area is called doldrums because sailors in olden days used to get becalmed here. It’s the region of weak winds (small pressure gradients), High Humidity and High Temperatures occuring heat near equator.

Horse Latitude:- In olden days, Zones at about 30 N/S Degree were known as Horse latitude. When ships were becalmed, horses were thrown to reduce the load. Here, the air is…

New Tropical Wave Could Affect The Country This Coming Weekend

The month of October is the worst of the rainy season. Typical forecasts are rain, rain, and more rain. The difference this year is, even more, rain than usual.

From the national weather service

As the country recovers from the effects of tropical storm Nate, a new tropical wave (number 43) could affect the country next weekend as the Inter-Tropical Convergence Zone, or ITCZ continues to generate…