Earth Gauge » Atmosphere

Climate Trivia: Earth’s Green Season

kraus — Mon, 08 Mar 2010 15:01:01 +0000

In the Northern Hemisphere, deciduous trees are beginning to come out of their dormant season and unfurl their leaves. Soon, the greys and browns that characterize America’s broadleaf forests during winter will be replaced the by the greens of spring and summer. Over the last four decades, there has been a global trend in the length of the “green” season, or the period between when leaves emerge in the spring and when they turn color and drop in the fall.

Trivia Question: Since 1970, Earth’s “green” seasons have become…

a) longer
b) shorter

The correct answer is a. Earth’s “green” season – the combined average length of both the Northern and Southern Hemisphere green seasons – is now on average 15 days longer than it was in 1970. This trend has been linked to warmer temperatures, milder winters and higher concentrations atmospheric carbon dioxide.

Seasons: Late Winter, Early Spring

Source: Peñuelas, J et al. “Phenology Feedbacks on Climate Change.” Science 324 (2009): 887-888.

Climate Number: Two Tons

kraus — Mon, 01 Mar 2010 14:57:07 +0000

Over the past 250 years, the amount of carbon dioxide (CO2) in the atmosphere has risen from 280 parts per million to almost 400. Plants use sunlight to convert this atmospheric carbon into the sugars and starches that make up their tissues. As the amount of carbon in the atmosphere changes, plant growth patterns change as well. Longer growing seasons, the period of the year when freezing temperatures do not restrict growth, as well as warmer temperatures in general, also affect plant growth. All three of these climate trends (more CO2, longer growing seasons and higher temperatures) have been occurring in the forests of America’s Mid-Atlantic region over the past century. During this period, plant growth in these forests accelerated. Each acre accumulates a certain amount of “biomass” each year, which reflects how much carbon these forests take out of the atmosphere and store in their bodies. Each acre of Mid-Atlantic forest is now accumulating about two more tons of biomass each year than they did in 1900.

For Comparison: Two tons is about the same weight as two mature Hereford bulls.

Seasons: Spring, Summer, Fall

Sources: McMahon, SM et al. “Evidence for a recent increase in forest growth.” Proceedings of the National Academy of Sciences 107 (2010): 3611-3615 and “Forests are Growing Faster, Ecologist Discover; Climate Change Appears to be Driving Accelerated Growth.” Science Daily 2 February 2010. Accessed Online 28 February 2010 )

Climate Fact: Prairie Plant Response to CO2 Enrichment

kraus — Mon, 22 Feb 2010 15:17:11 +0000

Changes in the amount of carbon dioxide (CO2) in the air have been shown to affect plant growth rates, the amount and quality of fruit plants produce and how much water a plant releases through evaporation. A study conducted between 1996 and 2001 in the western Great Plains (parts of Colorado and Wyoming) grew several species of native and invasive prairie plants under both elevated and current CO2 concentrations and temperatures. The plants communities grown under elevated CO2 concentrations and temperatures produced about twice as much plant matter as the communities grown under today’s conditions. This growth, however, was accompanied by a decrease in the amount of nutrients the plant matter held. Also, plant species considered to be of poorer quality for livestock became more prevalent under the elevated CO2 and temperature conditions.

Seasons: Winter, Spring, Summer, Fall

Source: Parton, WJ et al. “Projected ecosystem impact of the Prairie Heating and CO2 Enrichment experiment.” New Phytologist 174 (2007): 823-834.

Climate Fact: Midwinter Storm Track Suppression

kraus — Mon, 22 Feb 2010 15:15:29 +0000

The temperature/pressure difference between the equatorial regions and the poles is at its maximum during the winter months. The energy this difference generates is thought to power the “storm tracks,” or the bands in the mid-latitudes where east to west traveling storms (cyclonic high and low pressure systems) are most common. The storm track over the Pacific brings the western U.S. ample rainfall for much of the fall, winter and spring seasons. One aspect of Northern Hemisphere winter storm behavior that has been somewhat of a mystery is the midwinter suppression of the Pacific storm track. The maximum latitudinal temperature/pressure difference during winter, which means more power for the storms, is reflected in the Atlantic storm track being at its strongest during the winter months. Over the Pacific, however, the midwinter corresponds to an average decrease in the number and strength of these storms by 20 and 14 percent respectively compared to the fall and spring months. One possible explanation for this suppression is a wintertime drop in the number of atmospheric disturbances that make their way from the mountains of central Eurasia to the Pacific. These disturbances can become the storms that move across the Pacific to North America. The sheer size of the Eurasian landmass means that the wintertime high pressure centers that sit in the middle of the continent are strong enough to push the warmer and competing air masses far to the south and away from the mountains where these warmer air masses can generate the disturbances that can ultimately become the Pacific storms.

Season: Winter

Source: Penny, S et al. “The Source of the Midwinter Suppression in Storminess over the North Pacific.” Journal of Climate 23 (2010): 634-648.

Climate Fact: North American and Eurasian Snow

kraus — Mon, 22 Feb 2010 15:13:48 +0000

Snow is both a product of the weather and a weather maker. It has long been recognized that snow exhibits a cooling effect on local and regional scales. Snow reflects more sunlight than bare ground, meaning that it absorbs less energy. More snow cover also means soils stay moist for longer following the spring melting than they otherwise would. More soil moisture means that more of the sun’s energy that would have been spent heating the ground is instead spent evaporating water. In North America, lots of snow over the continent affects the storm track, or the latitudinal band where travelling cyclonic high and low pressure systems are most common. More specifically, the cold temperatures the snow cover induces eventually force the storm track over North America to veer south. As it does this, the storm track downstream in Eurasia veers north, allowing warmer air masses to penetrate further into the continent than they otherwise would. The presence of these warmer air masses generally means less snow there. Thus, years of above average snow cover in North America tend to be years of below average snow cover in Eurasia.

Seasons: Winter, Spring

Source: Sobolowski, S et al. “Modeled Climate State and Dynamic Responses to Anomalous North American Snow Cover.” Journal of Climate 23 (2010): 785-799.

Climate Trivia: Ocean vs. Atmosphere Carbon Stocks

espinoza — Mon, 08 Feb 2010 13:56:38 +0000

Carbon is a critical element in the Earth system. Carbon molecules are constantly moving from different states and from reservoir to reservoir. One reservoir is the terrestrial biosphere (the life systems that exist on land), which holds carbon primarily in the form of plant matter and soil. The atmosphere holds carbon in the form of carbon-dioxide gas (CO2) and methane. The oceans also hold carbon, primarily in the form of dissolved CO2 and calcium carbonate. The amount of reactive carbon – carbon in forms that can readily change its chemical state and move from one reservoir to another – in each of these reservoirs is markedly different. The ocean is by far the largest of these three carbon reservoirs.

Trivia Question: The ocean’s carbon reservoir is about how many times the size of the atmosphere’s carbon reservoir?

a. Two times
b. Ten times
c. 25 times
d. More than 60 times

The correct answer is d. The oceans hold more than 60 times the amount of reactive carbon that the atmosphere does.

(Source: Riebesell, U et al. “Sensitivities of marine carbon fluxes to ocean change.” Proceedings of the National Academy of Sciences 49 (2009): 20602-20609)

Climate Trivia: Earth’s Largest Dust Source

espinoza — Mon, 08 Feb 2010 13:50:31 +0000

At any given time, there is about 22 million tons of dust suspended in the atmosphere around us. Dust has important effects on Earth’s climate. It absorbs and scatters incoming radiation, affecting how much sunlight reaches the Earth’s surface and how much is reflected back into space. How much sunlight reaches the Earth’s surface helps drive surface temperatures and rainfall patterns. Dust also serves as a fertilizer – dust from barren regions can travel thousands of miles and fertilize plants that grow in lush regions. The Amazon rainforest is one such lush region that is stimulated by fertilizing dust from afar.

Trivia Question: What region is Earth’s largest single source of atmospheric dust?

a. The Great Basin
b. The Gobi Desert
c. The Sahara Desert
d. The Atacama Desert

The correct answer is c. More dust comes out of Africa’s Sahara Desert than any other region on Earth. The Bodélé Depression in Chad (central Africa) may be Earth’s largest single dust “hot spot.” About half of the dust emitted from the Sahara comes from this 8650 square mile barren lake bed. Each year, about 100 dust plumes rise from the depression. Each plume contains about 700,000 tons of dust.

(Source: Grini, A et al. “Model simulations of dust sources and transport in the global atmosphere: Effects of soil erodibility and wind speed variability.”Journal of Geophysical Research – Atmospheres. 110 (2005): D02205 and Washington, R. et al. “Dust as a tipping element: The Bodélé Depression, Chad.” Proceedings of the National Academy of Sciences 49 (2009): 20564-20571)

Climate Trivia: Ocean vs. Atmosphere Heat Capacity

espinoza — Mon, 08 Feb 2010 13:39:51 +0000

Even if the sun’s energy suddenly stopped, Earth would still give off heat for a while. This is because while much of the sun’s energy is reflected back into space, much of the energy that does reach the Earth is “stored” by the atmosphere, the oceans and the land. These bodies gradually release accumulated solar energy back into space in the form of long-wave or infrared radiation. The oceans are an especially complex energy storage system, with an elaborate network of currents that move heat from the surface to the depths and from the tropics to the poles. Water has a higher heat capacity than air, which means it takes far more energy to raise the temperature of a given volume of water than a given volume of air. One consequence of this higher heat capacity is that the oceans store more energy than the surrounding atmosphere.

Trivia Question: The ocean’s heat capacity is approximately how many times larger than that of the surrounding atmosphere?

a. Two times
b. Ten times
c. 100 times
d. 1000 times

The correct answer is d. The oceans hold about 1000 times as much heat as the atmosphere does. Over the past 50 years, the Earth has warmed. During this period, the oceans accumulated about 20 times the amount of heat the atmosphere accumulated.

(Source: Riebesell, U et al. “Sensitivities of marine carbon fluxes to ocean change.” Proceedings of the National Academy of Sciences 49 (2009): 20602-20609)

Climate Number: Five Trillion Gallons

kraus — Mon, 01 Feb 2010 15:39:54 +0000

While commonly considered two separate lakes, Lakes Michigan and Huron are actually hydrologically one body of water – they are connected at the Straits of Mackinaw and rise and fall in unison. Since 1980, Lake Michigan-Huron has been warming and annually averaged surface temperatures are now 3.6 degrees Fahrenheit warmer than they were in the late 1970’s. This warming has been accompanied by less wintertime ice cover and more evaporation from the Lake’s surface. While about half of this 25 percent increase in evaporation is accounted for by increases in summertime evaporation, more water is evaporating from the lakes during the spring, fall and winter seasons as well. The decline in ice cover means that there is now more liquid water exposed to late fall and winter winds, which pick up the moisture from the Lake and deposit it down-wind in the form of lake effect snow. Increases in Great Lake lake effect snow have been observed during this same period when ice cover has declined. This 25 percent annual increase in evaporation from the Lake means that over five trillion more gallons of water are going into the atmosphere from the lakes each year than during a typical year in the 1970’s. This increase helps to explain why lake levels have been declining over the last few decades despite above average regional precipitation totals. Water levels in Lake Michigan-Huron have been hovering around long-term record lows since 2000.

For Comparison: Five trillion gallons is about the same amount of water stored in the reservoir created by China’s Three Gorges Dam on the Yangtze River. Five trillion gallons is also about how much water is allocated annually to seven western states and Mexico under the 1922 Colorado Water Compact, which is based on estimates of the annual flow of the Colorado River at that time.

Seasons: Winter, Spring, Summer, Fall

Sources: Hanrahan, JL et al. “Connecting past and present climate variability to the water levels of Lakes Michigan and Huron.” Geophysical Research Letters 37 (2010): L01701 and National Geographic: Global Action Atlas. Colorado River Project Summary (2009). Accessed Online 1 February 2010 and Dangerfield, Whitney. “Snapshot: Yangtze River.” Smithsonian.com 1 September 2007. Accessed Online 1 February 2010 and Source: Burnett, AW et al. “Increasing Great Lake-Effect Snowfall during the Twentieth Century: A Regional Response to Global Warming.” Journal of Climate 16 (2003): 3535-3542.

Climate Number: $16.3 Billion

kraus — Mon, 01 Feb 2010 15:37:37 +0000

When put in 2000 US dollars, freezing rain (ice storm) events in America caused an estimated 16.3 billion dollars in total losses between 1949 and 2000 due to downed power lines, downed trees, agricultural losses, transportation accidents and medical costs from injuries due to slippery conditions. Freezing rain events are most frequent in the Northeast, but are also common across the Midwest and Piedmont regions from North Carolina northward. When freezing rain events hit the Southeast they tend to be accompanied by high dewpoints. This means that while ice storms are rarer in the Southeast, they tend to be heavy and particularly damaging when they do hit. Records kept since the late 1920’s show that ice storms were the least frequent during the 1930’s and rose to a peak in the early 1950’s, showing little or no trend thereafter.

For Comparison: 16.3 billion dollars is around the same amount collectively pledged by all participating parties to fight global poverty following the 2008 U.N. anti-poverty summit. It is also roughly the same amount as NASA’s annual budget.

Seasons: Winter

Source: Houston, TG et al. “Freezing rain events: a major weather hazard in the conterminous United States.” Natural Hazards 40 (2007): 485-494.

Climate Number: 100 Million Metric Tons

kraus — Mon, 01 Feb 2010 15:35:39 +0000

In the Southern Ocean around Antarctica, strong winds accompany strong ocean currents that move carbon from the ocean surface to the depths and from the depths to the surface. This ocean is considered to be a “Carbon dioxide (CO2) sink,” or a component of Earth’s climate that takes in more atmospheric CO2 as carbon concentrations in the atmosphere increase. It is also believed to be an important mechanism in the deglaciation process following ice ages, when atmospheric carbon concentrations are low, by “outgassing” more CO2 into the atmosphere than it absorbs. In today’s climate, it is estimated that the Southern Ocean takes in between 100 and 600 million metric tons of carbon ever year.

For Comparison: Americans consume about 100 million metric tons of concrete each year. While this may sound like a huge number, it is small compared to the total amount of CO2 exchange between the oceans and atmosphere each year, which is about 1000 times that amount.

Seasons: Winter, Spring, Summer, Fall

Sources: United Nations Conference on Trade and Development. “Review of Maritime Transport 2004.” Accessed Online 1 February 2010 and Le Quéré, Corinne et al. “Saturation of the Southern CO2 Sink Due to Recent Climate Change.” Science 316 (2007): 1735-1738 and Yuan, X and Martinson, DG. “The Antarctic Dipole and its Predictability.” Geophysical Research Letters 28 (2001): 3609-3612.

Climate Fact: Lake Warming in California and Nevada

kraus — Mon, 25 Jan 2010 14:29:50 +0000

Air temperatures are fickle – they fluctuate significantly from day to day, from season to season and from year to year. The temperature of a water body fluctuates as well, but is much more constant than the surrounding air temperature. Water has a higher heat capacity than air, which means it takes far more energy to raise the temperature of a given volume of water than a given volume of air. It also means that once warmed, the water must lose lots of energy to fall in temperature. This higher heat capacity causes seasonal changes in water temperature to “lag” behind the ambient air temperature. This phenomenon is easily observable. The air temperature can remain below freezing for weeks before ice cover begins to form on lakes. The higher heat capacity of water means that temperature fluctuations on multi-annual time scales in lake water as a whole are much smoother than temperature fluctuations in the atmosphere, making lakes effective indicators of longer term warming or cooling trends. Records from satellite imaging systems that collect nighttime infrared emissions show that several large lakes in the Sierra Nevada region (Tahoe, Mono, Pyramid, Almanor and Clear Lake) have collectively been warming at a rate of 0.2 degrees Fahrenheit per year since 1992. This trend may have implications for the life in these lakes that has adapted to the traditionally cold high-altitude temperatures.

Seasons: Winter, Spring, Summer and Fall

Source: Schneider, P et al. “Satellite observations indicate rapid warming trend for lakes in California and Nevada.” Geophysical Research Letters 36 (2009): L22402.

Climate Fact: Arctic Temperature Trend Amplification and the AMO

kraus — Mon, 25 Jan 2010 14:26:27 +0000

Temperature records suggest that the Earth’s surface temperatures warmed during the early part of the 20th century, cooled from the period 1940-1970 and have since been warming. While Arctic temperature trends have corresponded to this general warming and cooling pattern, it has followed these trends more severely. During the warming period from 1910-1940, the Arctic warmed about 5.4 times the rate of the rest of the planet and from 1970-2008 it warmed at about twice the rate. During the cooling period of 1940-1970 it cooled at about nine times the rate of Earth’s average trend. What is behind this temperature trend amplifications in the Arctic? The best explanation is the behavior of the Atlantic Multidecadal Oscillation (AMO), or the periodic 65-year warming and cooling of North Atlantic sea-surface temperatures due to a strengthening and weakening of the ocean currents that bring warm waters from the tropics into the far north. If the Atlantic had a cold anomaly in the far northern regions that was balanced by a warm anomaly in the subtropics, the Arctic would noticeably cool while the rest of the planet would show little or no change in temperature. The coincidence of warm AMO periods (warm waters in the Arctic) and cool AMO periods (cool waters in the Arctic) during periods of global warming and cooling respectively helps to explain why the Arctic has shown such severe warming or cooling trends compared to globally averaged rates.

Seasons: Winter, Spring, Summer, Fall

Source: Chylek, P et al. “Arctic air temperature change amplification and the Atlantic Multidecadal Oscillation.” Geophysical Research Letters 36 (2009): L14801.

Climate Fact: Antarctic Sea Ice

kraus — Wed, 13 Jan 2010 14:42:55 +0000

Much attention has been given to the decline of sea ice over the North Pole, which fell to a September minimum of 1.6 million square miles in 2007, about 40 percent below normal levels. On the other side of the world, the sea ice that extends from Antarctica’s continental ice sheets out over the ocean fluctuates between an average summertime (March) minimum extent of about 1.1 million square miles to an average of 6.9 million miles at the end of winter (September). In contrast to the Arctic ice, the average annual extent of the southern hemisphere ice has actually grown since the late 1970s at a rate of around one percent per decade. This trend has been linked to:

•   Ozone Depletion: The most pronounced rates of ozone depletion have occurred over Antarctica, where the ozone hole forms during the spring months. While the strong westerly winds that “trap” frigid air around the continent during winter make the ozone hole possible, the hole itself works as a feedback by accentuating the pressure difference between the continent and the mid-latitudes of the Southern Hemisphere. This works to strengthen the winds responsible for the ozone hole in the first place.
•   Wind Shifts: The accentuation of the pole to mid-latitude pressure difference linked to ozone depletion has deepened several of the continent’s low pressure zones, strengthening some of the winds that blow from the continent over the ocean during the autumn months. This has led to increases in sea ice over several of Antarctica’s coastal regions.
•   Freshwater on the Ocean Surface: Increased precipitation around Antarctica and melting of the glaciers that sit on the land have led to freshening of the ocean surface waters. This promotes ice formation.

Shifts in the winds have also caused decreases in sea ice extent in some areas of the continent – specifically parts of the Southern Ocean adjacent to the Indian Ocean and the Amundsen-Bellingshausen Sea sectors. These losses have been more than compensated for by gains in other areas.

Seasons: Winter, Spring, Summer, Fall

Source: Turner, J et al. “Non-annular atmospheric circulation change induced by stratospheric ozone depletion and its role in the recent increase in Antarctic sea ice extent.” Geophysical Research Letters 36 (2009): L08502.

Climate Fact: The Ozone Hole and Climate

kraus — Mon, 11 Jan 2010 15:28:14 +0000

Near the center of Antarctica in the polar vortex, strong westerly winds that blow in a circle around the continent during winter trap an envelope of air near the South Pole, prohibiting this air from mixing with warmer air masses closer to the equator. The extreme cold in the vortex causes clouds to form in the lower part of the stratosphere. Conditions in these stratospheric clouds are just right for a complex series of chemical reactions to take place, resulting in the destruction of ozone molecules and the formation of the ozone hole. This hole is at its maximum during the austral (Southern Hemisphere) spring months of September through December; stratospheric ozone concentrations during these months can fall by 33 percent. Once temperatures warm sufficiently, the strong westerly winds slow and the polar vortex breaks up, allowing ozone rich air to blow in and ozone poor air to blow out. This movement of ozone poor air is noticeable in parts of New Zealand and South America, where ozone concentrations can temporarily drop by 10 percent.

While the vortex is a local phenomenon, the strength and annual duration of the westerly winds that create the polar vortex are influenced by a larger phenomenon called the Southern Annular Mode (SAM), the difference in atmospheric pressure between 40 and 65 degrees South. When this difference is relatively large, the westerly winds around Antarctica are particularly strong, leading to a stronger vortex and more ozone destruction. High concentrations of ozone, however, can affect the movements of air between the stratosphere and troposphere, ultimately affecting the SAM itself. Better understanding this “coupling” between the SAM and the ozone hole will be needed for better weather and climate prediction, as well as for predicting future ozone concentrations.

Seasons: Winter, Spring, Summer, Fall

Sources: Sparling, B. “The Antarctic Ozone Hole.” NAS Educational Resources. 2001. Accessed Online 10 January 2009 and Fogt, RL et al. “Intra-annual relationships between polar ozone and the SAM.” Geophysical Research Letters 36 (2009): L04707 and Son, SW et al. “Ozone hole and Southern Hemisphere climate change.” Geophysical Research Letters 36 (2009): L15705.

Climate Fact: Antarctica’s Moisture Sources

kraus — Tue, 05 Jan 2010 21:35:41 +0000

Once water is evaporated from the ocean or a moist land surface, it may spend days traveling through the air. Complicated systems of winds at different levels of the atmosphere can transport moisture (as well as other gases and dust) from the point of origin to remote locations thousands of miles away. While about 30 percent of the moisture that rains or snows over Antarctica originates in the Southern Ocean close to the continent, the rest comes from latitudes north of 50 degrees South (about the same latitude as the southern tip of New Zealand). Ten percent comes from north of 30 degrees South (about the same latitude as Durban, South Africa). The higher elevations closer to the center of Antarctica have mean moisture origin sources north of 44 degrees South. During the summer, when there is less sea ice, more of Antarctica’s precipitation originates from the waters around the continent.

Seasons: Winter, Spring, Summer, Fall

Source: Sodemann, H and Stohl, A. “Asymmetries in the moisture origin of Antarctic precipitation.” Geophysical Research Letters 36 (2009): L22803.

Climate Trivia: East Coast Winter Storm Frequency and ENSO

kraus — Mon, 07 Dec 2009 15:59:51 +0000

December is East Coast Winter Storm (ECWS) season. These storms are powered by warm water that flows from the Gulf Stream. The Gulf Stream current flows along the Eastern Seaboard past Florida and the Carolinas before reaching Cape Hatteras, where the warm water heads out into the Atlantic. ECWS’s travel northward along the coast causing high winds and coastal property damage comparable to hurricanes. They also bring heavy snowfall, causing further weather complications. On average, there are 12 ECWS’s during the December to February season, with January being the most active month. One of the best predictors of how intense an ECWS season will be is the ocean temperature along the coast of the southeastern U.S. during the previous summer (Gulf of Mexico temperatures were above average this past summer). The warmer these waters are, the stronger the Gulf Stream generally is and the more active the winter storm season will be. Interestingly, conditions in the eastern tropical Pacific affect ECWS activity as well. What eastern tropical Pacific conditions are most conducive to an active ECWS season?

a)   El Niño conditions (warmer eastern tropical Pacific SSTs)
b)   La Niña conditions (cooler eastern tropical Pacific SSTs)
c)   Neutral Conditions (average eastern tropical Pacific SSTs)

The correct answer is a. More active ECWS seasons tend to coincide with El Niño years. This is in contrast to Atlantic hurricane season trends, as El Niño conditions tend to suppress Atlantic Hurricane formation. Over the second half of the 20th century, the frequency of ECWS events showed little trend, but the storms did become slightly more intense.

Season: Winter

Sources: DeGaetana, AT et al. “Statistical Prediction of Seasonal East Coast Winter Storm Frequency.” Journal of Climate 15 (2002): 1101-1117 and Hirsch, ME et al. “An East Coast Winter Storm Climatology.” Journal of Climate 14 (2001): 882-899 and Eichler, T and Higgins W. “Climatology and ENSO-Related Variability of North American Extratropical Cyclone Activity.” Journal of Climate 19 (2006): 2076-2093 and National Oceanic and Atmospheric Administration: Climate Prediction Center. Accessed Online 7 December 2009 http://www.cpc.ncep.noaa.gov/products/precip/CWlink/stormtracks/eisdiffobs.meta.gif

Climate Trivia: ENSO and Regional Rainfall (Northwest)

kraus — Mon, 07 Dec 2009 15:58:02 +0000

Winter storm season is here. Storms will be blowing in from the Pacific, bringing rainfall to lower elevations and snow to the mountains. This year, the eastern tropical Pacific is in an El Niño phase, meaning that its waters are warmer than average. When the eastern Pacific is in an El Niño phase, the northwestern U.S. can expect:

a)   more than normal rainfall
b)   less than normal rainfall
c)   about average rainfall

The correct answer is b. The Northwest gets less than normal rainfall during El Niño winters and greater than normal rainfall during La Niña winters, when the colder waters in the eastern Pacific cause the Pacific storm track to shift north and hit us. The storm track will spend most of its time south of us this winter, thus giving us below average rainfall through about April.

View a schematic diagram of how El Niño and La Niña events affect wintertime rainfall and temperature: http://www.earthgauge.net/climate-facts-image-library#5. For more information on El Niño, including seasonal forecasts by region, visit: http://www.elnino.noaa.gov/. Learn more about what Northern Hemisphere storm tracks are and how they work: http://www.earthgauge.net/wp-content/CF_Storm%20Tracks.pdf.

Season: Winter

Sources: Eichler, T and Higgins W. “Climatology and ENSO-Related Variability of North American Extratropical Cyclone Activity.” Journal of Climate 19 (2006): 2076-2093 and National Oceanic and Atmospheric Administration: Climate Prediction Center. Accessed Online 7 December 2009 (http://www.cpc.ncep.noaa.gov/products/precip/CWlink/stormtracks/eisdiffobs.meta.gif

Climate Fact: ENSO and Regional Rainfall (South)

kraus — Mon, 07 Dec 2009 15:54:44 +0000

a)   more than normal rainfall and cooler temperatures
b)   less than normal rainfall and warmer temperatures
c)   about normal rainfall and about normal temperatures

The correct answer is a. The South gets more than normal rainfall during El Niño years and less than normal rainfall during La Niña years when the colder waters in the eastern Pacific cause the Pacific storm track to shift north and miss us. During El Niño, not only does the storm track head right for us, it is even stronger than it is during the La Niña phase. Another effect of El Niño is cooler than normal winters in the South from about Texas eastward.

View a schematic diagram of how El Niño and La Niña events affect wintertime rainfall and temperature: http://www.earthgauge.net/climate-facts-image-library#5. For more information on El Niño, including seasonal forecasts by region, visit: http://www.elnino.noaa.gov/. Learn more about what Northern Hemisphere storm tracks are and how they work: http://www.earthgauge.net/wp-content/CF_Storm%20Tracks.pdf.

Seasons: Winter

Climate Trivia: ENSO and Regional Rainfall (Southwest)

kraus — Mon, 07 Dec 2009 15:50:46 +0000

Winter storm season is here. Storms will be blowing in from the Pacific, bringing rainfall to lower elevations and snow to the mountains. This year, the eastern tropical Pacific is in an El Niño phase, meaning that its waters are warmer than normal. When the eastern Pacific is in an El Niño phase, the southwest U.S. can expect:

a)   more than normal rainfall
b)   less than normal rainfall
c)   about normal rainfall

The correct answer is a. The Southwest gets more than normal rainfall during El Niño years and less than normal rainfall during La Niña years when the colder waters in the eastern Pacific cause the Pacific storm track to shift north and miss us. During El Niño, not only does the storm track head right for us, it is even stronger than it is during the La Niña phase. Hopefully, this El Niño winter will give the Southwest some relief from the current dry and drought conditions.

Season: Winter