The Change of Seasons: Views from Space

A major snowstorm blanketed the United Kingdom in early December 2010. Much greener isles can be seen in an autumn image from several years ago. Images like these help weather forecasters in the United Kingdom track weather systems, watch for the development of severe weather and identify when certain weather systems will clear specific locations. The image of the snow-covered islands validates forecasts of where snow will fall and shows the extent of its coverage across the country.

These images were taken by the Moderate Resolution Imaging SpectroRadiometer on NASA's Terra satellite.

The change in seasons is vividly displayed in four satellite images of Lake George, New York. Snow covers the land in winter, the first greening of vegetation pops up in spring, the landscape is green with plants in summer and finally, fall colors show the green vegetation is dwindling.

These images allow scientists to study the same place at different times of year. This helps scientists learn how different plant types respond to changes in temperature, amount of daylight and rainfall. Over time, variations in normal patterns may be observed. Changes in plants are caused by various factors, including drought, excessive heat or cold and insect infestation.

The four satellite images (taken in different years) were captured by the Advanced Spaceborne Thermal Emission and Reflection Radiometer on NASA's Terra satellite.

Throughout history, the rising and falling waters of the Nile River have directly impacted the lives of the people who live along its banks. Dramatic changes in the water level can be seen from space.

The waters of the White Nile (western branch) and Blue Nile (eastern branch) converge in Khartoum, the capital of Sudan. The rivers join to form the Great Nile and flow northward towards Egypt and the Mediterranean Sea. The growth of the White Nile can be easily seen between spring and summer. In 2001, heavy rains in the Blue Nile area also led to extensive flooding in the Great Nile.

When there are no clouds to cover a satellite's view of the land, images like these help identify and map flood-inundated areas. The images were taken by the Multi-angle Imaging SpectroRadiometer on NASA's Terra satellite.

NASA satellites have been tracking a trend showing a loss of sea ice in the Arctic Circle. Less ice means more open water in the ocean and, over time, this can bring significant changes to a wide region. The maps show the extent of ice at the beginning of fall. The time around the fall equinox marks the lowest extent of ice left after summer's warming and ice melting. Red tones indicate more perennial (older and thicker) ice, while green tones show younger, thinner ice and blue represents the ocean. The circle around the North Pole is an area where no data were available.

By 2005, Arctic sea ice decreased to a record low, compared to results from all satellite data gathered in prior years since the 1970s. Also, most of the sea ice east of Greenland disappeared from 2001 to 2004, compared to normal conditions. In 2007 (the image is not shown here), sea ice extent broke the 2005 minimum record, a record minimum that has not been broken since. Closely monitoring sea ice throughout the seasons gives scientists a view on important changes to the Arctic. NASA's QuikScat satellite collected global data, including data on Arctic sea ice extent, from 1999 to 2009.

The Amazon River flows more than 4,000 miles across South America. By volume, it is the largest river in the world. The world's largest rainforest is in the Amazon River Basin.

The amount of water stored in the basin varies from month to month. From space, NASA's twin GRACE satellites measure the amount of water by looking at changes to Earth's gravity field. When the Amazon River flow is high, there is greater mass in the basin; when the river is low, the mass is lower. In these images, red shows a greater mass in the Amazon and blue shows less mass. Spring is when the waters are highest and fall is when they are lowest.

Scientists use information like this to monitor water storage throughout the world. They watch for changes in normal patterns so communities may have warnings if their water supply patterns are changing.

These maps show the temperature of the air at Earth's surface. Surface air temperature is what we experience every time we are outdoors. The difference in temperature between day and night is very familiar, but these maps are a combination of daytime and nighttime. Very warm average surface temperatures (40 degrees Celsius /104 degrees Fahrenheit) are seen over the deserts in the summer hemisphere (see Africa in July). Cooler surface air temperatures are found at higher elevations in the tropics and subtropics, including the Andes. The coldest temperatures are found at highest latitudes, especially in wintertime (northern hemisphere January and southern hemisphere July). The very coldest temperatures are found in the high-altitude Antarctic Plateau in winter.

Warmest and coldest temperatures are found over land, because land both warms and cools rapidly. In contrast, the ocean surface temperatures are more regular because the ocean warms only very slowly. This prevents very high day-to-day surface temperature changes over the ocean. The ocean is also effective in warming an overlying cold atmosphere. The coldest surface air temperatures over the oceans are found in winter just downwind (east) of Asia and North America. As that cold air moves over the ocean it warms, giving warmer surface air temperature on the upwind (west) sides of the wintertime continents.

The data for these maps comes from the Atmospheric Infrared Sounder on NASA's Aqua satellite.

These global maps show a quantity commonly called 'precipitable water vapor.' Water vapor plays a major role in Earth's water cycle because its condensation leads to clouds, then rain and snow. This precipitation leaves behind heat, with major effects on motion in the atmosphere.

If all water vapor stored in the atmosphere were to fall to Earth, the colors on the map represent the depth of the resulting layer of water, in units of milliliters. Blue shows the largest amount of water vapor in the atmosphere (an equivalent surface layer up to 2 to 3 inches in depth), green indicates about 1 inch of water vapor, and light tan a half inch or less.

The area around the equator is home to the largest amount of water vapor, where it evaporates from the warm tropical ocean. The atmosphere's ability to contain moisture is strongly related to its temperature. Warmer air is likely to have more water vapor. Motion in the atmosphere also controls water vapor. Air from the wet tropics moves towards Earth's poles, often in distinct 'atmospheric rivers' (see the green 'rivers' moving toward the poles on the maps). As this air moving towards the poles cools, the precipitable water vapor falls as rain or snow, leading to a dry polar atmosphere. Water vapor amounts are greatest in the summer hemispheres because of their warmth. In January, the southern hemisphere has more water vapor but by July, the water vapor moves northward.

The data for these maps comes from the Atmospheric Infrared Sounder on NASA's Aqua satellite.

The snow-covered landscape is the easiest change to see between winter and summer around Salt Lake City, Utah. Another is the different coloration between the northern and southern portion of the Great Salt Lake. In 1953, a rock-filled causeway was built to support a permanent railroad. This causeway has resulted in decreased circulation between the two parts of the lake and higher salinity on the northern side.

The city sits near the southeastern shore of the Great Salt Lake Mountains, including the Wasatch Range to the east, surround the city.

The images were taken by the Multi-angle Imaging SpectroRadiometer on NASA's Terra satellite.

To learn more about how NASA studies Earth, go to:

> NASA's Global Climate Change Website

> NASA's Climate Kids Website