from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A line drawn on a weather map or chart linking all points of equal or constant temperature.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A line of equal or constant temperature on a graph or chart, such as a weather map.
from the GNU version of the Collaborative International Dictionary of English
- n. A line connecting or marking points on the earth's surface having the same temperature. This may be the temperature for a given time of observation, or the mean temperature for a year or other period. Also, a similar line based on the distribution of temperature in the ocean.
- n. A line on a graph connecting points representing states having the same temperature; an isothermal line.
from The Century Dictionary and Cyclopedia
- n. A line connecting points on the earth's surface having the same mean temperature.
- n. In mathematics, a curve representing phenomena which happen at constant temperature.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. (meteorology) an isogram connecting points having the same temperature at a given time
The treeline is generally coincident with the summer JJA 10°C isotherm, although some argue the isotherm is a response to the treeline because of albedo changes, accumulation of snow and reduced wind speeds.
The 10C (50F) isotherm, which is cold, is within 500 meters of the 30C (86F) surface.
There are some who argue that the isotherm is a response to the treeline not as generally assumed.
"The well-visualized ice margin by ultrasound CT or MR is actually only the 0-degree Celsius line, or isotherm, which is not sufficiently lethal to cancer cells, but has unfortunately been confused with the actual treatment margin.
The present northern distribution coincides with the July 15°C isotherm and is likely to shift northward with climate change.
The weak trend in September temperatures at 2 m is largely explained by the proximity of the 0 ºC isotherm and the latent heat of the associated phase change.
Koppen (1931) uses this line, which coincides approximately with the 50F (10C) isotherm of the warmest month, as a boundary between subarctic and tundra climates.
For example, in the Polar Ural Mountains over the 90 years of study, the upper treeline rose 20 to 40 m in altitude but the June – July temperature isotherm rose 120 to 130 m.
This means that the June – July isotherm rose 120 to 130 m in altitude (in this area the elevational temperature gradient is 0.7 °C/100 m).
The boundary between the two is the isotherm of 72F (22C) for the warmest month.