anemometer: an instrument that measures wind speed. The air is less dense than the surrounding air and travels upward along a slope. anabatic wind: winds caused by warm air close to Earth's surface. Also called atmospheric pressure or barometric pressure. air pressure: the pressure exerted by the weight of air over a given area of Earth's surface. The time of day when temperature and pressure differences are greatest, and therefore the breezes are strongest, is midafternoon, when land reaches its maximum WORDS TO KNOW adiabatic process: a process by which the temperature of a moving air parcel changes, even though no heat is exchanged between the air parcel and the surrounding air. They lose intensity as they travel inland or out to sea. Sea breezes and land breezes are strongest at the shoreline, where temperature and pressure differences are most pronounced. The resultant land breeze flows from the high-pressure area, over the shore, out to the low-pressure area, over the water. At night, the process is reversed as the land loses heat more quickly than does the water. A mild wind blows across the pressure gradient, from the high-pressure area (over the water) to the low-pressure area (over the land). As a result, a low-pressure area develops over warm ground and a high-pressure area over the cooler water. Sea breezes form on hot days because the land warms more rapidly than does the water. A land breeze, in contrast, blows from the shore toward the water. It comes as a welcome relief to coastal inhabitants on a hot day. A sea breeze blows from the water to the shore. Sea breezes and land breezes are two familiar categories of local winds that are driven by differences in temperature and in air pressure, which is the pressure exerted by air on a given area.

In addition, local winds have many interesting and descriptive names. Regardless of their cause, local winds have certain general characteristics. Local winds can be driven by temperature and pressure differences or by variations in topography, the shape and height of Earth's surface features. A local wind can persist anywhere from several minutes to several days. Mesoscale winds are better known as local winds or regional winds. Story by Kathryn Hansen.Mesoscale winds are winds that blow across areas of the surface ranging from a few miles to a hundred miles in width. NASA Earth Observatory images by Joshua Stevens, using MODIS and VIIRS data from LANCE/EOSDIS Rapid Response. Moist sea breezes combine with valley winds and move up toward the mountaintops. As the land warms during the day, the temperature difference between the land and sea surfaces causes winds to blow onshore. Sea breezes could have contributed to the cloud growth, too. As the warm, moist air rises, it cools and condenses into clouds over the volcanoes. Turn on the image comparison tool to see the difference.Īccording to Joshua Qian of the University of Massachusetts, the clouds are the result of a meteorological phenomenon called “ valley wind.” During the day, the Sun warms the air in the valleys and by afternoon causes it to rise up the slopes of the mountains. local time (03:00 Universal Time), the clouds had not yet formed.

Earlier that day, when the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra passed over at about 10 a.m. local time (05:51 Universal Time), the Visible Infrared Imaging Radiometer Suite (VIIRS) on Suomi NPP captured the top image of clouds ringing the volcanoes.

However, they were influenced by the volcanic topography.īoth images were acquired on May 19, 2017. But the white areas surrounding the volcanoes in the top image do not have a fiery origin: they are clouds. Many are active, intermittently spewing plumes of ash into the atmosphere. The Indonesian island of Java is famous for its volcanoes, which run through the island’s center like a spine.

Valley breeze