![]() ![]() The remnants of Lake Chad appear in olive-green amid the tan and light brown hues of the surrounding landscape where the countries of Chad, Niger, Nigeria and Cameroon all share borders. Once heaved aloft, the dust can be carried for hundreds or even thousands of kilometers. The small grains of the silty sand are easily swept up by the strong wind gusts that occasionally blow over the region. As the waters receded, the silts and sediments resting on the lakebed were left to dry in the scorching African sun. But persistent drought conditions, coupled with increased demand for freshwater for irrigation, have reduced Lake Chad to about 5 percent of its former size. In the mid-1960s, Lake Chad was about the size of Lake Erie. Once serving as part of the floor for a much larger Lake Chad, the area now known as the Bodele Depression, located at the southern edge of the Sahara Desert in north central Africa, is slowly being transformed into a desert landscape. Lake Chad, Africa February 7 and 11, 2004. The high energy levels of these storm systems typically make them hazardous due to associated heavy precipitation, lightning, high wind speeds and possible tornadoes. The image, taken while the International Space Station was located over western Africa near the Senegal-Mali border, shows a fully formed anvil cloud with numerous smaller cumulonimbus towers rising near it. The photo was taken from a viewpoint that was at an angle from the vertical, rather than looking straight down towards the Earth’s surface. The cloud tops flatten and spread into an anvil shape, as illustrated by this astronaut photograph. The tropopause halts further upward motion of the cloud mass. Beyond the tropopause, the air no longer gets colder as altitude increases. The tropopause is characterized by a strong temperature inversion. If enough moisture is present to condense and heat the cloud mass through several convective cycles, a tower can rise to altitudes of approximately 10 kilometers at high latitudes and to 20 kilometers in the tropics before encountering a region of the atmosphere known as the tropopause-the boundary between the troposphere and the stratosphere. This leads to the characteristic vertical “towers” associated with cumulonimbus clouds, an excellent example of which is visible in this astronaut photograph. This type of convection is common in tropical latitudes year-round and during the summer season at higher latitudes.Īs water in the rising air mass condenses and changes from a gas to a liquid state, it releases energy to its surroundings, further heating the surrounding air and leading to more convection and rising of the cloud mass to higher altitudes. The air mass itself also expands and cools as it rises due to decreasing atmospheric pressure, a process known as adiabatic cooling. Surface air is warmed by the sun-heated ground surface and rises if sufficient atmospheric moisture is present, water droplets will condense as the air mass encounters cooler air at higher altitudes. Once logged in, click "HTTP" under the charts on this page to access the data.Perhaps the most impressive of cloud formations, cumulonimbus (from the Latin for “pile” and “rain cloud”) clouds form due to vigorous convection (rising and overturning) of warm, moist and unstable air. Note: You now need to create an Earthdata account to access NASA's ice sheet data. ![]() Meltwater coming from these ice sheets is responsible for about one-third of the global average rise in sea level since 1993. They are losing ice due to the ongoing warming of Earth’s surface and ocean. This is important because the ice sheets of Greenland and Antarctica store about two-thirds of all the fresh water on Earth. This record includes new data-processing methods and is continually updated as more numbers come in, with a delay of up to two months. ![]() ![]() The GRACE Follow-On mission began collecting data in June 2018 and is continuing to monitor both ice sheets. Antarctica is losing ice mass (melting) at an average rate of about 150 billion tons per year, and Greenland is losing about 270 billion tons per year, adding to sea level rise.ĭata from NASA's GRACE and GRACE Follow-On satellites show that the land ice sheets in both Antarctica (upper chart) and Greenland (lower chart) have been losing mass since 2002. ![]()
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