Purevjav G.,Institute of Meteorology and Hydrology IMH |
Balling R.C.,Arizona State University |
Cerveny R.S.,Arizona State University |
Allan R.,UK Met Office |
And 12 more authors.
International Journal of Climatology | Year: 2015
A World Meteorological Organization (WMO) committee evaluated the record sea-level pressure (SLP) measurement of 1089.4hPa on 30 December 2004 in Tosontsengel, Mongolia (1724.6m). Although instrumentation and data collection procedures were properly followed according to the assessment of the committee, concern was raised regarding the reliability of SLP adjustment from such a high-elevation station. This paper addresses this concern with a number of analyses that look at relationships between SLP extremes and corresponding station elevation and temperature. First, we selected data from stations extracted from the Integrated Surface Database (ISD-Lite) of NOAA's National Climate Data Center. A spatial analysis indicates that elevation shows little to no association (R2 values essentially zero) to extreme SLP. However, a second analysis between extreme SLP and air temperature indicates that high regionalism exists in spatial correlations (local R2) between those two variables. This relationship to temperature is likely the result of differences in SLP adjustment formulae used around the world. Based on this analysis, on the need to differentiate the SLP values adjusted using extremely cold temperatures (and generally high elevation), and following past WMO SLP guidelines, the WMO Rapporteurs for Climate and Weather Extremes therefore have created two distinct SLP records: (a) highest adjusted SLP (below 750m), currently 1083.3hPa recorded on 31 December 1968 at Agata, Evenhiyskiy, Russia; and (b) highest adjusted SLP (above 750m), currently 1089.4hPa (by Russian method; 1089.1hPa by WMO formula) on 30 December 2004 in Tosontsengel, Mongolia. Future WMO guidance regarding SLP adjustment may lead to re-evaluation of this and other SLP records. © 2015 Royal Meteorological Society.
News Article | December 28, 2015
SAN FRANCISCO — Why are there so many songs about rainbows? Perhaps because there are so many different types, each with its own distinctive features, new research suggests. There are 12 types of rainbows, distinguished by various characteristics, the study suggests. Fat droplets of water or tiny sprays of mist will affect them, along with the angle of the sun. Rainbows can even appear as twins, triplets or quadruplets, Jean Ricard, a researcher at the National Meteorological Research Center, in France, said here yesterday (Dec. 17) at the annual meeting of the American Geophysical Union. And even a single rainbow is always changing, he said. "They don't look alike because when we look at a rainbow, one second later, the drops which form the primary bow and the secondary bow are not the same, because they are falling," Ricard said here in a news briefing. "If you look carefully after a few minutes you will start to see some changes in each rainbow." [Infographic: Earth's Atmosphere – Top to Bottom] Scientists have understood the basics of rainbow formation since at least Descartes' time: Sunlight interacts with water droplets in the sky, and the light is both reflected and refracted as it enters and leaves the raindrop. Because different wavelengths of light — which correspond to different colors — slow down by different speeds when they hit a raindrop, the different colors get bent at different angles, separating into the rainbow's distinctive hues. (The bizarre phenomenon known as a fire rainbow is neither a fire nor a rainbow, because it occurs when light refracts through ice crystals, not raindrops.) In the past scientists tried to classify rainbows based on the colors in the rainbows, or the size of the droplets they refracted through. But those classifications often missed certain types of rainbows. To capture all the myriad "flavors" of rainbows, Ricard and his colleagues tried to figure out the minimum set of characteristics that would describe all rainbows. It turns out that rainbows can have up to four characteristics . There is the primary bow, with red on top and blue-violent on the bottom. Above that, secondary reflections inside a rain droplet always form a secondary, fainter bow above the primary bow, with the colors reversed. Between the two is a dark region, called Alexander's band, where little light from the raindrops light reflects. And sometimes, there are additional bows, called supernumerary bows, which may occur when the light rays spread and cancel each other out via diffraction and interference in the atmosphere. Based on those characteristics, they determined there are 12 different types of rainbows, with imaginative names like RB_1, RB2, etc. The rainbows vary by whether all colors are visible, whether they have a strong Alexander's band, and whether there are supernumerary bows. Some of the more striking rainbows include only red arcs, and then there are yellow-and-orange rainbows. When Ricard and his colleagues analyzed the physics, they found that the height of the sun in the sky was the biggest single factor affecting the rainbow's appearance. For instance, when the sun is very low in the sky, such as at sunset, light is much less intense and must travel much farther to reach the eye. Only the red wavelengths are able to make it through the atmosphere at this time, he said "At sunset or sunrise, the color of the sun and the intensity of the incoming light changes dramatically," Ricard said. The size of the droplet also affected a rainbow's appearance, though to a lesser degree. Wider drops make for less vivid rainbows with more widely spaced hues, he said. While rainbow research may seem more suited to daydreamers and poets, it may have practical applications, Ricard said. For instance, if scientists can spy rainbows on exoplanets, that may be a sign of atmospheric water. And where there's water, there's often life. Copyright 2015 LiveScience, a Purch company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.