New satellite promises unprecedented data on clouds and aerosols

Image of EarthCARE satellite in orbit

Credit: ESA/ATG medialab

A new satellite called EarthCARE to be launched later this month will provide unprecedented data on clouds and aerosols that will help ECMWF to initialise its weather forecasts.

EarthCARE is a joint venture between the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA). It is the sixth satellite of ESA’s Earth Explorer Programme, and it will be operational for at least three years.

In addition to providing valuable new data to help establish the conditions in the atmosphere at the start of forecasts, EarthCARE’s instruments are optimised for quantifying the size of cloud droplets and ice crystals in clouds.

Indeed, ECMWF scientists are leading the development of EarthCARE’s official ‘synergy’ product, combining the various instruments to estimate cloud properties. These data will be used to evaluate ECMWF forecasts and to improve the representation of physical processing in the model.

“This satellite comes at a crucial time for weather and climate science, so we are extremely excited to see it ready for deployment in space,” says Marta Janisková, an ECMWF scientist who has helped to prepare our systems for the data.

Helping to initialise forecasts

Satellites have a prominent role for ECMWF forecasts. An important way in which data from EarthCARE will be used at ECMWF is to help determine the initial conditions of forecasts.

Two of the four instruments carried by the satellite will be useful for this purpose. The Atmospheric Lidar (ATLID) will provide vertical profiles of aerosols and thin clouds, and the Cloud Profiling Radar (CPR) will provide vertical profile measurements of clouds. It will also observe vertical velocities of cloud particles through Doppler measurements.

EarthCARE's view of clouds and precipitation

The CPR instrument will provide cross sections of clouds and precipitation. The colours indicate the density of the clouds and, below the horizontal line, the intensity of precipitation. The purple line at the top is what the ATLID instrument will see. Credit: ESA.

“The first step will be to monitor these observations. We will then provide feedback on data quality to ESA,” says Marta.

In preparation for the launch, ECMWF carried out tests showing that using EarthCARE’s data will be useful. These feasibility studies used historical observations from NASA’s CloudSat and CALIPSO satellites.

The results were encouraging: they showed that the analysis of weather conditions, which serves as the starting point for weather forecasts, is improved when CloudSat and CALIPSO data are assimilated.

CloudSat radar reflectivity for the 00 UTC analysis on 1 August 2007


ECMWF model equivalent radar reflectivity for the 00 UTC analysis on 1 August 2007

Cross sections of observed CloudSat radar reflectivity (top) and of the ECMWF model equivalent analysis radar reflectivity (bottom) corresponding to various portions of orbital track inside a 12-hour assimilation window for the 00 UTC analysis on 1 August 2007. For details, see the article in ECMWF Newsletter No. 162.

The techniques developed for CloudSat and CALIPSO will have to be adjusted to EarthCARE, but they provide a good starting point. The CPR and ATLID observations can then be used to help establish the location, density, and vertical extent of clouds and aerosols with unprecedented accuracy.

“There will be close cooperation with validation teams at ESA, who will also benefit from us evaluating the satellite’s data,” says ECMWF scientist Mark Fielding.

Atmospheric composition and evaluation

At a later stage, ATLID observations from EarthCARE are also expected to be assimilated into forecasts of atmospheric composition. These are separately operated by the EU’s Copernicus Atmosphere Monitoring Service (CAMS), implemented by ECMWF. The observations will help determine the aerosol content in the atmosphere.

CALIPSO and Aeolus satellite images of aerosol plume

This image shows tracks of the CALIPSO satellite (back) and the Aeolus satellite (front) crossing an aerosol plume north of South America in June 2020. The plume has left a distinctive signature in the satellite observations and would have been seen with even greater clarity by EarthCARE.

In addition to assimilating data, EarthCARE measurements will also be useful to evaluate both cloud cover and air quality forecasts provided by ECMWF.

“The novelty in ATLID is that it can measure very accurately how clouds and aerosols interact with solar and thermal radiation,” says ECMWF scientist Robin Hogan.

Atmospheric Lidar on the EarthCARE satellite

Image of the Atmospheric Lidar (ATLID) on the EarthCARE satellite. Credit: ESA/ATG medialab.

The CPR instrument also provides new possibilities relevant for evaluation. “What’s new in the CPR instrument is that it can measure the speed of the particles, so for the first time we’ll be able to see how fast rain and snow are falling,” Robin says.

“We can use EarthCARE data to evaluate and improve the representation of clouds, precipitation and aerosols in our models.”

Cloud Profiling Radar on the EarthCARE satellite

Image of the Cloud Profiling Radar (CPR) on the EarthCARE satellite. Credit: ESA/ATG medialab.

The other two instruments on EarthCARE, the Multi-Spectral Imager (MSI) and the Broad-Band Radiometer (BBR), will also be used in the evaluation of ECMWF forecasts and of climate models. They will serve in particular to evaluate the impact of clouds and aerosols on radiative fluxes.

Excitement after a long wait

The planned use of EarthCARE comes after several delays to the project, which was originally proposed over 20 years ago.

“We are very pleased and excited that EarthCARE is to launch later this month,” says Mark. “After years of preparatory work, we should be able to make good use of it.”