| Section A | A index | 411-419 of 917 terms |
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almanac—A calendar to which astronomical and other data (often weather related) are commonly added.
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Almeria–Oran front—A frontal region in the western Mediterranean Sea between Spain and Algeria that separates salty Mediterranean surface water from inflowing Atlantic water. It marks the transition from hydraulic control of the Atlantic inflow through the Straits of Gibraltar to geostrophic control of the flow. The front is associated with a strong current that feeds into the Algerian Current.
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almwind—Local name for a foehn that blows from the south (Hungary) across the Tatra Mountains south of Krakow, Poland, and descends the northern valleys; similar to the Alpine south foehn. It is sometimes stormy and may reach 20–25 m s−1 (40–50 mph) in gusts, especially in spring and fall. It raises temperatures to as much as 14°C above the normal for the season, and in winter and spring it causes avalanches. At Zakopane (in southern Poland) it sometimes blows as a high foehn. This wind occurs in front of depressions moving eastward in the Baltic.
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along-slope wind systems—Thermally forced winds that blow up or down the sidewall slopes in a mountain valley, and the accompanying countercurrents when present; the slope-wind components of the mountain–valley wind system. During the daytime this system consists of upslope (anabatic) flow adjacent to the slope and often a compensatory return current directed downslope just above the upslope layer. At night it is a downslope (katabatic) flow layer near the slope, sometimes with a return flow aloft.
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along-valley wind systems—Thermally forced winds blowing along the main (longitudinal) axis of a valley, sometimes accompanied by countercurrents aloft; the up- and down-valley components of the mountain–valley wind systems. During the daytime, this system comprises an up-valley wind and its countercurrent if present. At night it is a down-valley wind and return flow if present.
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along-valley winds—The component of topographically generated winds that are parallel to the valley axis and can occur during conditions of light or calm synoptic-scale winds such as those near the center of anticyclones. At night, cold, dense air flowing down the river valley from the higher elevations is called a mountain wind or drainage wind with typical depths of 10 to 400 m and speeds of 1 to 8 m s−1, while the weaker return circulation aloft is called an anti-mountain wind. During the day, the gentle up-valley flow of warm air along the valley floor is called a valley wind, and the return circulation aloft is called an anti-valley wind. Compare cross-valley winds, anabatic wind, katabatic wind.
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aloup de vent—A cold night wind in the vicinity of the valley of Brevenne in France.
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alpenglow—The occasional reappearance of sunset colors on a (snow-covered) mountaintop soon after sunset and a similar phenomenon before sunrise. Alpenglow has three phases. During evening twilight, the first stage is the mountain peak's usual coloration seen at low sun elevations h0 (h0 < 2°). Second is the alpenglow proper that occurs a few minutes after the first color has faded (h0 slightly less than 0°). The peaks are still in direct sunlight, and their colors are purer and often pinker than before. The alpenglow boundary may first occur hundreds of meters below the summit, then moves upward, and finally fades as the atmosphere's dark segment rises. Third is the afterglow, which occurs nearly simultaneously with the first purple light. The peaks are no longer in direct sunlight; the illumination is more diffuse and its boundary vaguer than in the earlier stages. The third stage lasts longer than the other two (−5° < h0 < −9°), and its color varies from yellow to purple. A faint second afterglow has been reported and is associated with the rare occurrence of a second purple light. The alpenglow appears to be much less common at sunrise than at sunset. The morning colors are more pink and purple, while those of evening are more orange and red.
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