WES WEEK FOUR: 1-5 October 2001

• More California water problems foretold -- Another winter with inadequate moisture could present more problems for California farmers and hydroelectric utilities. Planning meetings are attempting to assess the conditions during the current 2001 water year that will end on 30 September, inspect the long-range weather forecasts and help users coupe with possible continued drought conditions. [ENN]
• Changes in Arizona climate and health considered -- A report issued by the Physicians for Social Responsibility considers the potential effects that a change in the climate of Arizona during the next 100 years could have upon the health of residents of the Grand Canyon State. Increased heat indices, which combine the effects of high temperatures and high humidities could, could adversely affect residents. Increased incidence of flash flooding is also possible. [ENN]
• Listening for ocean on Europa -- Scientists at MIT are using acoustic techniques to determine if the Jovian satellite Europa has large quantities of water under its crust. [EurekAlert!]

• Brazilian hydropower problems -- An unexpected appetite for electricity coupled with drought conditions have necessitated the expansion of the largest hydroelectric dam along the Brazilian-Paraguayan border. [CNN]

• Updated analysis of atmosphere-ocean poleward heat transport (wonder about 'saving' for later in term? RSW) Using [UCAR]
• An assessment of the weather across the nation for the 2001 Summer -- In a recent press release, the National Climate and Data Center reports that the just concluded summer of 2001 (the three month interval of June through August) was the fifth warmest since nationwide records commenced in 1895. While nationwide average precipitation totals for the summer were close to the long-term average, the Southeast, Gulf Coast, northern Plains experienced wetter than average conditions, while the West Coast remained relatively dry. [NOAA News]
• Earth diary - A summary of the week's major environmental events on Planet Earth. [CNN]

Concept of the Week: Controlling Indoor Humidity

In public buildings as well as individual homes, it is sometimes desirable to alter extremes of relative humidity so that living spaces are more comfortable. For human comfort, optimum relative humidity lies between about 30% and 50%. When indoor air is exceptionally dry, a humidifier may be used to add water vapor to the air, but when indoor air is excessively muggy, a dehumidifier may be used to remove water vapor from the air.

As cold, dry winter air is drawn indoors and heated by a furnace, its relative humidity declines--sometimes to uncomfortably low levels. Suppose, for example, that outdoor air has a temperature of -20° C (-5° F) and relative humidity of 50%. If that air were brought indoors and heated to 21° C (70° F), its relative humidity drops to about 2%--well below the optimal winter indoor relative humidity of 30% to 50%. At such very low relative humidity values, people often feel discomfort caused by dry skin and irritation of the mucous membranes in their nose and throat. Also, wood furniture dries out and may crack and become unjointed. Discharge of static electricity (e.g., after walking across a carpet and touching a metal doorknob) can be a nuisance in dry rooms.

One remedy for excessively low indoor relative humidity is a device known as a humidifier. A humidifier elevates the relative humidity of indoor air to more comfortable levels by evaporating water into the air (increasing the vapor pressure). A common humidifier design consists of a wheel that continually rotates a porous belt (or pads) into and out of a reservoir of water. A fan blows air through the wetted belt, water evaporates into the air stream, and the more humid air circulates through the dwelling.

On the other hand, a dehumidifier may be desirable during warm muggy summer days. In addition to discomfort caused by reduced evaporative cooling, high values of indoor humidity can cause increased incidence of mold and mites. A dehumidifier lowers the relative humidity of indoor air to more comfortable levels by inducing condensation of water vapor (decreasing the vapor pressure). In a standard dehumidifier, a fan draws humid air past a cold refrigerated coil. Air in contact with the coil is chilled to saturation, water vapor condenses on the coils and drips from the coils into a collection reservoir or through a hose into a drain. Most dehumidifiers function best when the air temperature is at or above 18° C (65° F).

Click on forecast map for locations across the country where today's indoor relative humidity is expected to be too high or too low in the absence of any controls on indoor humidity. For an interactive applet (from the University of Wisconsin) that explores the relationships between temperature, dewpoint, and relative humidity, go to http://profhorn.meteor.wisc.edu/wxwise/museum/a7/a7exercise1.html. Follow instructions and note how the indoor relative humidity changes with changes in outdoor conditions.

Concept of the Week: Questions

1. A humidifier elevates the relative humidity by causing [(evaporation)(condensation)].
2. A dehumidifier reduces the relative humidity by causing [(evaporation)(condensation)].

• 1 October 1893...The second great hurricane of the 1893 season hit the Mississippi Delta Region drowning more than 1000 persons. (David Ludlum)
• 1 October 1997... Flash flooding in Nogales, AZ resulted from 2 to 3 inches of rain. One hundred homes and 30 businesses were flooded and five vehicles floated down Western Avenue. (Accord Weather Calendar)
• 2 October 1867...A hurricane struck Galveston, TX with a storm tide that produced $1 million damage. (Intellicast)
• 2 October 1882...A major hurricane struck the Louisiana Delta with 100-mph winds and 12-foot storm tide which inundated the bayous resulting in 1500 deaths. (Intellicast)
• 3 October 1841... The "October Gale", the worst of record for Nantucket, MA, caught the Cape Cod fishing fleet at sea. Forty ships were driven ashore on Cape Cod, and 57 men perished from the town of Truro alone. Heavy snow fell inland, with 18 inches near Middletown, CT and 3 inches at Concord, MA. (David Ludlum)
• 3 October 1912...The longest dry spell of record in the U.S. commenced as Bagdad, CA went 767 days without rain. (David Ludlum)
• 4 October 1869...A great storm struck New England. The storm reportedly was predicted twelve months in advance by a British officer named Saxby. Heavy rains and high floods plagued all of New England, with strong winds and high tides over New Hampshire and Maine. Canton, CT was deluged with 12.35 inches of rain. (David Ludlum)
• 4 October 1986...Excessive flooding was reported along the Mississippi River and all over the Midwest, from Ohio to the Milk River in Montana. In some places it was the worst flooding of record. Rainfall totals for the week included 20.07 inches at Hale, KS, nearly 18 inches at Coffeyville and Walnut, KS. (Sandra and TI Richard Sanders - 1987) (Intellicast)
• 5 October 1786...The famous "Pumpkin Flood" occurred on the Delaware and Susquehanna Rivers. Harrisburg, PA reported a river stage of twenty-two feet. The heavy rains culminated a wet season. (David Ludlum)
• 5 October 1972...Heavy rains, mostly the remnants of Tropical Storm Joanne, fell across much of Arizona. It was believed to be the first time in Arizona weather history that a tropical storm entered the state with its circulation still intact. The center was over Flagstaff early on the 7th. (3rd-7th) (The Weather Channel)
• 5-7 October 1999...A storm southeast of New Zealand caused surf to reach heights of 12 feet along the south shores of all the Hawaiian Islands, flooding some roads and parking lots. The lobby of the Kihei Beach Resort on Maui and three ground floor units were flooded. (Accord Weather Calendar)
• 6 October 1967...Canada's 24 hour rainfall record was established at Ucluelet Brynnor Mines in British Columbia with 19.24 inches. (Accord Weather Calendar)
• 7 October 1737...A furious cyclone in the Bay of Bengal caused a major disaster at the mouth of the Hoogby River near Calcutta, India. As many as 300,000 people were killed, mainly as the result of the storm's forty foot high surge. (Accord Weather Calendar)

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URL: WES:/news.html
Prepared by AMS WES Central Staff and Edward J. Hopkins, Ph.D., email hopkins@meteor.wisc.edu
© Copyright, 2001, The American Meteorological Society.