Monthly Archives: January 2012

Weather Journal of Lewis and Clark

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I recently came across the book, Lewis and Clark: Weather and Climate Data from the Expedition Journals, edited by NWS meteorologist Vernon Preston.

Ever since my visit to the Jefferson National Expansion Memorial (Gateway Arch) in St. Louis, Missouri, I have been interested in the amazing journey of Meriwether Lewis and William Clark.  Between May 1804 and September 1806, these explorers traveled 4,162 miles from the Mississippi River to the Oregon Coast. Commissioned by President Thomas Jefferson, the “Corps of Discovery” had goals that were both scientific and commercial. Following their mandate, the expedition journals record the geography, flora, fauna, weather, and climate of the then uncharted territory of the American West.

Preston’s book focuses in on the weather and climate data found in the well-ordered journals.  It highlights both the positive and negative impacts the weather had on the expedition as well as how the explorers dealt with the elements. The book also supplements the journal data with route descriptions and historical maps.

A highly detailed book, it would be at home in the library of anyone interested in both meteorology and history.

Route of the Lewis and Clark Expedition

Image Credit: Wikipedia

Ancient Climate of the Tall Grass Prairie

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While traveling in the Mid-West not too long ago, I enjoyed a visit to the Tall Grass Prairie National Preserve in the Flint Hills region of Kansas. When you hike through its beautiful open landscape, the limestone beneath the grass stands out as evidence of past climate change.

Climate can shape the geology of a region in many ways.  In this case, the freezing and thawing of glaciers affected the existence of an ocean that covered much of present-day Kansas and Oklahoma.  Today’s vast “sea of grass” was once the bed of the Permian Sea. According to scientists, this shallow sea rose and fell numerous times during the Permian Period of the Paleozoic Era, about 251-299 million years ago.

This ancient sea sustained an array of aquatic-life, including fish and plants.  Just like today, these marine organisms took calcium carbonate out of the water to form their shells and skeletons.  After they died, these prehistoric sea creatures fell to the ocean floor where their stored calcium carbonate accumulated to form limestone over time.

These layers of sedimentary rock and the fossils they contain give us a much different view of America’s heartland than we are used to today.

Open landscape at the Tall Grass Prairie National Preserve, Kansas.

Limestone at Tall Grass Prairie National Preserve, Kansas.

Photo Credit: MF at The Weather Gamut

Paleoclimatology

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Weather records, in some form or another, go back to early human civilizations.  There are, however, other longer-term records captured in nature. Today, scientists read these proxy weather sources in an effort to better understand the causes of previous climate changes and make forecasts about our future climate.

Tree ring sections provide excellent climatic histories of specific regions, usually going back several hundred years.  Generally, the rings are thicker in warm, wet growing seasons and thin during periods of drought.  They can also display evidence of wildfires.

Glacial ice is an excellent environmental record keeper.  Formed in seasonal layers, each band conveys information about the climatic conditions that existed when the ice formed.  The air bubbles trapped in the ice are particularly valuable, as they provide direct samples of past atmospheric compositions.  Some ice cores provide climate information dating back more than 100,000 years.

The rock record is another window that allows scientists to look into prehistoric climates. Sedimentary rocks are valuable sources of information as they often capture the environmental character of a region from millions of years ago.  Their composition, as well as the fossils found within them, can indicate the rise and fall of ancient sea levels.

The diverse research of Paleoclimatology has given us a detailed view of how Earth’s climate has changed throughout its long history. We have also come to understand that climate and human activities have a significant relationship.  Our activities influence climate and, in turn, climate effects how we live.

First Snow of 2012 in NYC

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On Saturday, New York City received 4.3 inches of snow in Central Park.  This was our first significant snowfall of the season.  The city’s last measurable snowfall was back in October during a surprising pre-season snowstorm.

This winter has been relatively mild, so it was exciting to finally see some snow on the ground.  The local forecast, however, is calling for a major warm up this week.  As a result, this snow will not last long.  However, with more than two months left to the winter season, I am guessing that the snow will be back before long.

Central Park's Lake frozen and covered in snow.

The Sheep's Meadow in Central Park covered by a blanket of snow.

Photo Credit: MF at The Weather Gamut

Converting Fahrenheit and Celsius

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There are many different scales by which temperature can be measured.  In weather, we most often use Fahrenheit or Celsius.

Gabriel Daniel, a German physicist, developed the Fahrenheit scale in 1714.  It marks water’s boiling point at 212°F and its freezing point at 32°F.  In 1742, Anders Celsius, a Swedish astronomer, formulated a new scale intended for scientific use.  It designates the melting point of ice at 0°C and the boiling point of water at 100°C.

Today, most of the world uses the Celsius scale.  In the U.S., however, Fahrenheit is still our official unit of measure for temperature.  To convert between the two scales, use the formulas below.

To convert from Fahrenheit into Celsius: Tc = (5/9)*(Tf-32)

To convert from Celsius into Fahrenheit: Tf = ((9/5)*Tc)+32

Image Credit: Gringer

Weather and Art: Crossing the Delaware

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“Washington Crossing the Delaware” by Emanuel Leutze, is an iconic image of the American Revolution. The weather depicted in the painting, however, may not be accurate.

A new version of this celebrated subject by artist Mort Künstler explores some of these inaccuracies.  Through the research of historical documents, Künstler learned that the actual crossing took place under the cover night and in the midst of a nor’easter.  The artist also learned that the troops and equipment were probably transported on flat-bottomed ferries attached to cables that helped stabilize them in the storm.  Depicted in more realistic conditions, the painting’s main subject is still a determined George Washington.  However, it shows the general in the pragmatic posture of holding on to a cannon as he braces himself against the elements, which included strong winds, snow, and freezing rain.

Leutze created his better-known image in 1851, seventy-five years after the courageous events of December 1776.  His painting is an artistic interpretation that emphasizes the heroic status of General Washington. This is evident in the way he portrays the general illuminated by sunlight and standing tall in a rowboat as he crosses the icy Delaware River. The shape of the ice, in fact, is another questionable aspect of this classic painting. When frozen, the Delaware tends to form broad sheets of ice as opposed to the chunky crags that Leutze chose to illustrate.

After four years of renovations to its American Wing, the Metropolitan Museum Art returned Leutze’s work to public display earlier this week.  Künstler’s new painting entitled, “Washington’s Crossing: McKonkey’s Ferry, Dec. 26, 1776”, was unveiled at the New York Historical Society last month.

Emanuel Leutze's 1851 "Washington Crossing the Delaware"

Image Credit: Emanuel Leutze via Metmuseum

Mort Künstler's 2011, "Washington's Crossing: McKonkey's Ferry, Dec. 26, 1776”

Image Credit: Mort Künstler via AP

Winter and the Jet Stream

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The local forecast is calling for a big dip in the jet stream this weekend.  This will drive cold air south over New York City and send temperatures plummeting from their above average readings. You may wonder, what is this meteorological phenomenon that is bringing winter back to the city so abruptly?

Jet streams are bands of strong winds in the upper atmosphere that mark the location of the strongest temperature contrast at the surface. They are born out of the complex interactions among a variety of atmospheric conditions, including the position of warm and cold air masses, and the location of areas of high and low pressure.

In the U.S., the polar jet stream, one of four major global jets, marks the divide between cold arctic air and mild mid-latitude air. Its position is a function of temperature contrasts and therefore shifts throughout the year, depending on the season. In the warm summer months the jet is typically located around 50° to 60°N latitude.  In the winter, when temperature contrasts are increased, it usually shifts to the south.  It has been known to plunge as far south as 30°N latitude.

This winter, however, the jet stream has been staying well to the north with only a few arctic outbreaks so far.  When they do come though, the sudden drop in temperature can be very jarring.

Average seasonal positions of the Polar Jet Stream in the northern hemisphere.

Image Credit: ncsu.edu

Weather and Art: John Constable

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On a recent visit to the Yale Center for British Art, I was enchanted by the cloud studies of John Constable.  He was an English Romantic painter who believed, “…the sky is the source of light in nature, and governs everything.”

Constable is well known for his grand landscapes that emphasize atmospheric phenomena and mood.  His sketch canvases, however, tell us even more about his fascination with the weather.  On the back of his cloud studies, he recorded the weather conditions that existed while he painted.  For example, on the back of the cloud study painted on September 13, 1821, the artist wrote,  “1 o’clock, slight wind at NW, which became tempestuous in the afternoon, with rain all the night following.”

Interested in the developments of the atmospheric sciences of his time, Constable is reported to have owned a copy of Thomas Forster’s Researches About Atmospheric Phenomena.  This book included Luke Howard’s 1802 scientific paper, Essay on the Modification of Clouds, which outlines the classification system for clouds that is still used today.  A self described “man of clouds”, Constable believed, “we see nothing truly till we understand it.”

Constable's "Study of Cirrus Clouds"

Constable's "Seascape Study with Rain Cloud"

Image Credit: John Constable via Wikipedia

A Brief Blast of Winter

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Earlier this week, New York City was sent into a deep freeze.  After a very mild December, winter finally found us, if only for a short while.

This arctic plunge brought the city its coldest air of the season to date. Temperatures remained below freezing for two consecutive days. Wednesday marked our coldest day since late January of last year with a low temperature of 13°F.

This cold weather, however, did not last long.  Warmer air returned by the end of the week and temperatures quickly rebounded to above average readings.  This warm weather is very odd for January.  Nonetheless, the local forecast is calling for a continuation of these spring-like conditions into next week.

We will have to wait for the Jet Stream to dip south again for winter to return.

Graphics Credit: MF at The Weather Gamut

Perihelion

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Today, the Earth will reach its Perihelion at 8 P.M. Eastern Standard Time.  This is the point in the planet’s orbit where it comes closest to the Sun.

This annual event is due to the elliptical shape of the Earth’s orbit and the off-centered position of the Sun inside that path.  The exact date of the Perihelion differs from year to year, but it’s usually in early January…winter in the northern hemisphere.  We will be furthest from the Sun at the Aphelion in July.

The planet’s distance from the Sun does not cause the seasons, but it does influence their length.  As a function of gravity, the closer the planet is to the Sun, the faster it moves. Today, the Earth is about 146 million kilometers away from the Sun.  That is approximately 5 million kilometers closer than in early July.  This change in distance allows the planet to speed up by about one-kilometer/second.  As a result, winter in the northern hemisphere is about five days shorter than summer.  The opposite is true in the southern hemisphere.

The word, perihelion, is Greek for “near sun”.

The perihelion position of Earth's orbit.

Image Credit: Academy Artworks