The European Space Agency has launched the first of a new generation of weather satellites. This is set to revolutionise short-term weather forecasting in Europe, by providing better imagery at higher resolution and more frequently than before.
This new technology will help meteorologists keep track of sudden storms that can be devastating. That’s because the satellite will be able to resolve smaller cloud features, so they can virtually see them bubble up.
Infrared
There are a number of satellite weather systems that monitor the European region and provide information to meteorologists about Earth’s atmosphere. These include Geostationary Operational Environmental Satellites (GOES) and polar orbiting satellites that relay wind information near the ocean’s surface.
There is also an international mission called Jason-2 that flies an altimeter that measures sea level height and provides high-precision measurements of sea surface temperature. This information is crucial to detecting tropical storms as well as understanding how ocean currents affect the world’s weather.
Another satellite system that monitors Europe is Meteosat Third Generation, which carries an innovative instrument into the European weather forecaster’s toolbox. The MTG-I1 satellite, set to launch in 2024, carries an infrared sounder that will measure the temperature of various layers of the atmosphere and the amount of humidity. This will help improve the accuracy of so-called nowcasting models, which predict weather for the next several hours.
Infrared imagery enables a trained analyst to determine cloud heights and types, calculate land and surface water temperatures, and locate ocean surface features. It can also be used to detect fog and low clouds. Infrared images are useful for determining thunderstorm intensity by detecting cold cloud tops.
These satellites can detect thunderstorms early on and see them building in their earliest stages, before radars can spot them. This helps prevent the loss of lives and property.
Unlike visible imagery, which reflects sunlight, infrared images record the emission of longwave infrared radiation by clouds, land, oceans and snow and ice. This can be recorded day or night.
Infrared pictures show different colors based on the temperature of the clouds, allowing meteorologists to see the differences between clouds. Red and blue areas on infrared satellite images indicate cold (high) cloud tops, which are associated with very strong thunderstorms.
Infrared satellite images can also detect fog and low clouds, showing dark or white areas. This is because fog and low clouds reflect a lot of sunlight, making them brighter than nearby land or ocean surfaces. Infrared images can also identify ocean eddies or vortices, which are valuable to the shipping industry.
Visible
Most of the satellite images that we see in class have been recorded by a pair of weather satellites called Geostationary Operational Environmental Satellites, or GOES, which are operated by the National Oceanographic and Atmospheric Administration (NOAA). The GOES satellites orbit the Earth 22,000 miles directly above the equator once every 24 hours, keeping pace with the earth’s rotation.
They record several images per hour, which is the equivalent of about 13,000 pictures a day. Each one carries a different instrument, but all are designed to collect data that will improve Europe’s ability to forecast and monitor extreme weather.
The most impressive gizmo on the satellite, however, is an infrared sensor that measures temperature by detecting the radiation emitted by objects in Earth’s atmosphere. This data can be used to better estimate the temperatures of clouds, land and oceans, as well as to detect fires.
A second, much smaller instrument, is a lightning detector that will help meteorologists track down these powerful storms. It won’t be able to stop them from forming, but it will allow meteorologists to keep an eye on them in their earliest stages, before they become large enough to produce widespread damage.
Another innovative instrument is an imaging sensor that will help Europe’s weather forecasters see the planet in greater detail than ever before. It will deliver more frequent and accurate weather updates than its predecessors, which will help them issue timelier alerts to warn citizens of potential disasters.
The MTG imager will also carry a holographic display that can be used to show the locations of thunderstorms and lightning strikes. The display will not be operational for a few years, but it will be an improvement over the technology that was used on Europe’s previous weather satellites.
The MTG mission is also expected to improve detection and monitoring of wildfires, a common problem in many regions of the world as summer heatwaves grow more frequent. It will provide more timely information about the location and intensity of wildfires as well as better estimates of the size and direction of fires. This information could be used to better prepare communities for a disaster, and it may even prevent an outbreak of fires that can destroy property and kill people.
Radar
Radar is a technique that uses radio waves to detect and track objects. Originally developed during World War II to help in the battle for airspace, radar technology has since become widely used by governments and other agencies around the globe.
Weather radars monitor local storms such as hail, tornadoes and high winds. They also help scientists study severe weather such as hurricanes, and long-term climate processes in the atmosphere.
There are several different types of radars, but all have the same basic principles. They use microwave-wavelength radiation to transmit signals that reverberate in the atmosphere, like sound waves do when they hit water. These signals are then reflected by targets such as clouds or precipitation and measured, providing information about the object, such as its size, speed and direction of motion.
The amplitude (power) of the pulses that are sent out is determined by the radar’s Pulse Repetition Frequency, or PRF. This frequency is determined by the type of radar and its application. Smaller radars tend to have lower PRFs, while larger ones have higher PRFs.
For a radar to operate well, it must have a relatively low power level. This helps to avoid interference with other radio users, which could negatively impact the radar’s operation. The frequency of a radar’s signal must also be set to ensure it does not interfere with other radars operating at the same time.
Although radars are generally able to detect objects up to a few hundred miles away, this range is limited by the amount of energy they can send out. This is due to the diffraction effect that occurs when these waves pass through a dense atmosphere. In addition, ground clutter such as mountains can reduce the strength of radar echoes further out.
Some radars have a dual band, or multi-band, option that allows them to switch between two frequencies. This enables them to pick up different wavelengths of light, which provides additional supplementary information about terrain surfaces such as snow, ice and cloud cover.
There are a variety of weather radars in Europe, each specialized for specific applications. Some are dedicated to monitoring the surface of the Earth, while others monitor ozone or atmospheric aerosols. These radars can provide a wide array of measurements and are essential to the development of better forecasting systems for a variety of weather conditions.
Sounding
Satellite weather provides detailed information on the temperature, water vapor, ozone and precipitation of the atmosphere. These are essential parameters for numerical models used for forecasting weather and air quality. These instruments include infrared sounders, microwave radiometers and spectrometers that gather data from the Earth’s surface to derive atmospheric profiles of these key geophysical parameters (Ohring, 1979).
Infrared spectra of the radiances emitted by the Earth’s atmosphere at various wavelengths are measured by infrared spectrometers onboard satellites and can be retrieved and used in a wide range of applications including atmospheric climate research. The radiance measurements are then inverted to the geophysical parameters that are required for weather prediction models at numerical weather forecasting centers such as those run by ECMWF and NOAA.
As a result of the high rate at which these satellites collect observations, they are able to provide atmospheric profiles that have a much more accurate resolution than infrared spectrometers or ozone spectrometers on the ground. The higher resolution also allows for the measurement of important indices such as Convective Available Potential Energy (CAPE) that are needed by meteorologists to diagnose storm-scale updraft strength and potential.
These retrieved profiles of temperature, moisture and ozone are processed by the NOAA Unique Combined Atmospheric Processing System (NUCAPS) to produce Environmental Data Records. NUCAPS uses a multi-step retrieval process that includes cloud clearing and resampling the data to a standard latitude/longitude grid with a vertical resolution of 0.5 deg at fixed set of vertical levels.
Gridded soundings are particularly useful for operational forecasters, as they allow them to visualize the broad atmospheric environment quickly and above the boundary layer. They also allow forecasters to track gradients and min/max and trends in instability and moisture, which are useful for assessing the development of the weather system.
However, as pointed out earlier, soundings are volume measurements, not point observations, so they may underestimate important stability indices or features such as inversion layers near the ground when compared to radiosondes. This can lead to incorrect predictions of convective available potential energy (CAPE) values, and can lead to errors in the diagnosis of storm-scale updraft strength, especially during times of severe weather.