Clouds with Precipitation - Real-time

In this new layered version of two existing SOS datasets, we've combined Clouds - Real-time with Precipitation - Real-time to give a uniquely meaningful glimpse of global weather over the last month. Where you see bright colors over the clouds, there has been precipitation measured by satellites. Warm colors are rain and cold colors are snow.

Geostationary infrared satellite images are used by meteorologists to determine where clouds are, but more importantly, how the clouds are moving. The infrared, IR, satellites work by measuring the infrared radiation that is emitted. Because the emitted radiation is proportional to temperature, the data are converted to temperature values, which can be useful for meteorologists. In comparison to clouds, the Earth's surface, even on very cold nights, is warm. When there are clouds, they absorb the radiation emitted by the Earth below and emit their own radiation at a much cooler temperature. Any area that has clouds shows up cooler than the ground, allowing meteorologists to detect the locations of the clouds. The height of clouds is inversely proportional to temperature, meaning that the tallest clouds are the coldest. It is often the tallest clouds that bring the most severe weather.

The satellites that collect these data are geostationary, meaning that they rotate at the same rate as the Earth so that the satellites are over the same spot on Earth all the time. This allows them to collect a continuous stream of data for one location so that "movies" of the data can be made. Over the United States there are two such satellites, the GOES (Geostationary Operational Environmental Satellites) - East and GOES-West. There are many such satellites worldwide. This dataset is a composite of GOES, Meteosat, and MTSat satellite data. Meteosat and MTSat are similar to GOES, but are operated by other countries. This real-time dataset is shaded on a gray scale, meaning that the lowest clouds are a very light gray and the highest clouds are bright white. The "Blue Marble" is the background image for this dataset. Data for this visualization is available for the past thirty days.

Precipitation (falling rain and snow) that occurs around the globe is the source of fresh water on which all life depends. Even in the tropics, much of the precipitation begins as snow in the clouds high above the surface, then generally melts as it falls into warmer temperatures near the surface, except when the surface temperature is below freezing. The heaviest precipitation is found in the persistent band near the Equator, known as the Intertropical Convergence Zone (ITCZ). Just outside the ITCZ, more noticeably in the Northern Hemisphere, the tight swirls of tropical storms (including hurricanes and typhoons) can be seen occasionally in the northern summer. At subtropical latitudes in both hemispheres there are persistent dry areas associated with subtropical high pressure centers. The major deserts of the world occur in the subtropical highs, but these highs also cover vast regions of the oceans. At midlatitudes, the storm tracks display the swirls of low pressure systems and bands of frontal precipitation. [Note the opposite directions of circulation in the Northern and Southern Hemispheres!] Important year-to-year and shorter-interval variations cause strong modifications to local conditions, bringing droughts and floods.

Precipitation changes the naturally occurring microwave energy emitted by the Earth's surface and atmosphere. These signals are detected by satellite instruments that are attuned to specific microwave frequencies. In addition, a few satellites carry weather radars, providing data to adjust the estimates of precipitation from the microwave instruments. Finally, sometimes it is useful to estimate precipitation from information about cloudiness that is provided by infrared sensors flying on geostationary satellites (geo-IR).

This NASA GPM IMERG dataset is provided to Science On a Sphere in near-real time, about six hours after the observation. This dataset uses information from as many satellite microwave sensors as possible, and includes satellite radar data for calibration and geo-IR for additional information. The satellite data provide observations at each location about every three hours or less, and smooth transitions from one observation to the next are computed to give estimates every half hour.