EarthCARE satellite “Hakuryu” – All Observation Data Now Publicly Available!

The Japan Aerospace Exploration Agency (JAXA) and the European Space Agency (ESA) have developed the Earth Cloud Aerosol and Radiation Explorer (EarthCARE) satellite (Japanese nicknamed “Hakuryu”), which was successfully launched on May 29, 2024 (Japan Standard Time). JAXA and ESA will begin all standard products from the EarthCARE publicly available, providing insights into clouds, atmospheric particles (aerosols), and radiation budgets  . This article introduces an observation example of rain clouds spreading over the Japanese archipelago, captured by the EarthCARE on August 10, 2025, using the new product released this time.

EarthCARE is equipped with the Cloud Profiling Radar (CPR) developed by JAXA and the National Institute of Information and Communications Technology (NICT), as well as Atmospheric Lidar (ATLID), Multi-Spectral Imager (MSI), and Broadband Radiometer (BBR) developed by ESA.

JAXA has been collaborating with NICT, Kyushu University, the National Institute for Environmental Studies, Tokai University, the University of Tokyo, and the Remote Sensing Technology Center of Japan to develop data processing methods (algorithms) that estimate the physical properties of clouds, aerosols, and radiation from observation data. The products now being released include three-sensor synergy products of CPR, ATLID, and MSI, as well as four-sensor synergy products that incorporate BBR. With this release, all ten standard products developed by JAXA for the EarthCARE will become publicly available.

On August 10, 2025, at 5:00 UTC, the EarthCARE satellite passed near Osaka-city  and observed rain clouds extending from western to eastern Japan. At this time, localized heavy rainfall systems also formed over northern Kyushu. Figure 1 shows an observation video of clouds captured by the EarthCARE. A major feature of the EarthCARE is its ability to observe the internal structure of clouds.

Figure 2 combines a cloud image (in grayscale) observed from the Geostationary Meteorological Satellite Himawari-9 operated by the Japan Meteorological Agency  with the cloud optical thickness data (in color) observed by the MSI onboard the EarthCARE. This combination reveals how the rain clouds spanning western Japan to southeastern Tohoku exhibit a complex horizontal structure of cloud optical thickness.

The cloud radar (CPR) and the atmospheric lidar (ATLID) onboard the EarthCARE satellite observe the internal structure of clouds in detail. In the next section, we explain this structure using the “3-sensor synergy product (ACM_CLP)” and “4-sensor synergy product (ALL_RAD),” which integrates CPR and ATID, and the other sensor data.

Figure 1: EarthCARE satellite “Hakuryu” observing rain clouds over the Osaka-city in Japan at 5:00UTC on August 10, 2025 (video).

■CPR-ATLID-MSI Synergy Product: Cloud internal structure

One of the major challenges in predicting localized heavy rain lies in predicting the timing of individual cumulonimbus cloud development in advance. This uncertainty makes it difficult to forecast “how long the heavy rain will continue”. Before rain reaches the ground, small cloud droplets form in the atmosphere, grow, and eventually become raindrops. During this process, the size of the droplets and the strength of the updrafts within the cloud are key factors that closely influence hot the droplets develop.

Figure 3 shows a three-dimensional representation of clouds captured near Osaka. The vertical extent shows cloud droplet size (cloud effective radius) and the fall speed of precipitation particles, derived by the 3-sensor synergy product, “ACM_CLP”. These vertical details are primarily based on observations from CPR and ATLID, represented as two-dimensional cross-sections along the satellite track. On the horizontal plane, the figureshows the cloud optical thickness from the MSI single cloud product, MSI_CLP (the same MSI observation data used in Figure 2). CPR is the world’s first spaceborne sensor capable of observing Doppler velocities inside clouds, allowing detection of upward and downward speeds of particles and air within clouds. The CPR simultaneously observes the “backscatter intensity,” which indicates the strength of the radar signal return, and combining these measurements provides a more detailed understanding of the motion of cloud and rain particles, as well as the surrounding atmospheric motions. In Figure 3, the cloud particles size is smaller (in blue) in the upper layers and larger (in red) in the lower layers, indicating how particles grow as they descend and eventually become rain. The arrows highlight strong downward motion in the lower cloud layers, showing that precipitating large particles falling toward the ground. Observations that capture the internal structure of clouds like this deepen our understanding of how cloud particles grow into rain, contributing to improved accuracy in forecasting heavy rainfall events such as heavy rains and typhoons.

■4 Sensor Synergy Product: Heating and cooling profiles

Clouds and aerosols are deeply involved in the transfer of solar radiation and infrared radiation emitted by the Earth, significantly affecting the Earth’s climate and surface temperatures. However, substantial uncertainty remain in accurately quantifying the impact they have on the climate.

Clouds can heat the atmosphere by absorbing sunlight and infrared radiation from the Earth’s surface, but also cool the atmosphere by emitting infrared radiation into space. As global warming progresses, clouds may rise to higher altitudes or lower-level water clouds may thin, potentially leading to further enhance warming. On the other hand, it has also been pointed out that warming atmosphere lead to melting some ice clouds into liquid water, increasing the reflection of sunlight back to space and helping to partially suppresses warming. Thus, the impact of clouds on radiation is highly complex and remain insufficiently quantified. Therefore, clouds represent the largest source of uncertainty in predicting global warming. Reducing this uncertainty requires a detailed scientific understanding of cloud characteristics – such as their height, particles size and thickness, and how these characteristics affect atmospheric heating and cooling.

Figure 4 illustrats how rain clouds heat and cool the atmosphere, based on the 4-sensor synergy product, “ALL_RAD”. As shown in Figure 4, clouds evert both warming effects (shown in warm colors) and cooling effects (shown in cool colors). In particular, the upper layers of clouds that accompany precipitation show extensive blue areas, which can be interpreted as strong radiative colling caused by infrared radiation being emitted into space. On the other hand, the mid-level layers of the clouds show dominant heating from solar radiation.

As demonstrated in Figures 3 and 4, the EarthCARE mission provides consistent estimate of the radiative properties of clouds, which indicate whether the cloud heats or cools the atmosphere through the transmission of solar and infrared radiations, in addition to the microphysical properties of clouds – such as the size of cloud particles. These information are provided as part of the “3-sensor synergy products” and “4-sensor synergy products,” serving as fundamental data for comprehensive understanding of cloud internal structure and their radiative impacts.

■Towards improving climate change predictions

In the EarthCARE mission, the distribution of Level 1 products (for individual sensor) began in January 2025, followed by the distribution of the L2 products – including single-sensor product and two-sensor combined product combining CPR and ATLID – in March 2025. Level 1 products are observation data converted into engineering values, while Level 2 products are scientific data that have been converted into atmospheric physical quantities from Level 1 products. Level 2 products are further classified into single sensor products, created from individual sensor data, and synergy products, which integrate data from multiple sensors. The details on the types of products are found here.

The EarthCARE observation data is freely available to anyone through JAXA G-Portal and ESA websites.
• JAXA Earth observation satellite data provision system G-Portal
• ESA website

A major challenge in climate change prediction is to quantitatively understand how clouds change due to warming and how this affects the Earth’s radiation balance and precipitation formation. Improvements in observational technology and numerical models have advanced our understanding, although cloud and aerosol processes remains the largest source of uncertainty in climate projections, and it is still not fully understood whether they will amplify or, conversely, suppress future warming. By utilizing data from the EarthCARE – available from December 2025 – we aim to enhance the evaluation and improvement of climate models, contributing to more accurate climate predictions and the development of effective climate change adaptation strategies.