Conference Agenda

The CLIMATE-TPE project aimed to advance understanding the interactions between the Asian monsoon, the Tibetan Plateau surface and the plateau atmosphere in terms of water and energy budgets, which is essential for assessing and understanding the causes of changes in cryosphere, and hydrosphere in relation to changes of plateau atmosphere in the Asian monsoon system and for predicting the possible changes in water resources in the Third Pole Environment. A core innovation of the project was to verify or falsify recent hypotheses (e.g. links between plateau heating and monsoon circulation, snow cover and monsoon strength, soil moisture and timing of monsoon) and projections of the changes of glaciers and permafrost in relation to surface and tropospheric heating on the Tibetan Plateau as precursors of monsoon pattern changes and glaciers retreat, and their impacts on water resources in South East Asia. This paper reports results related to: (1) A platform of in-situ observation stations of hydrosphere-pedosphere-atmosphere-cryosphere-biosphere interactions over the Tibetan Plateau, (2) Multiyear in-situ L-Band microwave radiometry of land surface processes, (3) Evaluation and generation of land surface heat fluxes and evapotranspiration, (4) Climate scale monitoring of soil moisture and soil temperature and validation of large scale soil moisture products, (5) Trajectory of water vapor transport in the canyon area of Southeast Tibet, and (6) Vertical characteristics of water vapor exchange between upper troposphere and lower stratosphere.

The strong economic growth in China in recent decades, together with meteorological factors, has resulted in serious air pollution problems, in particular over large industrialized areas with high population density. To reduce the concentrations of pollutants, air pollution control policies have been successfully implemented, resulting in the gradual decrease of air pollution in China during the last decade, as evidenced from both satellite and ground-based measurements. The aim of the DRAGON4 project “Air quality over China” was the determination of trends in the concentrations of aerosols and trace gases, quantification of emissions using a top-down approach and gain a better understanding of the sources, transport and underlying processes contributing to air pollution. This was achieved through (a) satellite observations of trace gases and aerosols to study the temporal and spatial variability of air pollutants (b) derivation of trace gas emissions from satellite observations to study sources of air pollution and improve air quality modeling and (c) study effects of haze on air quality. In these studies, the satellite observations are complemented with ground-based observations and modeling.

The increase in atmospheric greenhouse gas concentrations of CO₂ and CH₄ due to human activities is the main driver of the observed increase in surface temperature by more than 1^oC since the pre-industrial area. To limit the increase in global surface temperature to 1.5°C, the 2015 United Nations Climate Change Conference held in Paris, most nations agreed to reduce greenhouse gas emissions.

Atmospheric observations of greenhouses gas concentrations from satellites will play an important tole for monitoring the effectiveness of any policies aimed at reducing emission. Satellite remote sensing of CO₂ and CH₄ is now well established thanks to missions such as NASA OCO-2, Japanese GOSAT and the Chinese TanSat missions which have allowed us to build a long-term record of atmospheric GHG concentration from space. They also give us a first glimpse into CO₂ and CH₄ enhancements related to anthropogenic emission which helps to pave the way towards the future missions aimed at a Moni­toring & Verification Support (MVS) capacity for the global stock take of the Paris agreement.

The pioneering GOSAT and OCO-2 missions have demonstrated the power of satellite observations to constrain surface fluxes of CO₂ and CH₄ and to inform on regional budgets but it has also emphasised the importance to utilise ground- based measurement to validate the satellite products and intercomparisons of multiple retrieval algorithms, especially to improve the accuracy of satellite retrievals to reduce the interference by many other factors, such as aerosols, clouds or ground surface properties.

The overall goals of this project has been to characterize and improve the TanSat XCO2 retrieval and their uncertainty quantification by retrieval intercomparisons and experiments using Chinese and European algorithms and by using TCCON and Chinese ground-based measurements and extend the validation previously applied for GOSAT and OCO-2 data to TanSat XCO2 and also analyse Sentinel 5 Precursor XCH4 observations. AirCore profile observations of greenhouse gases at Sodankylä has been used to support the validation at high latitudes. The XCO2 datasets obtained from TanSat have also been evaluated against model calculations and we have used XCO2 from satellites data to constrain surface fluxes over China and globally using surface flux inverse calculations.

In this presentation, we will describe the project, summarize the project objectives and give an overview over the project achievements.

The global wind field effects the atmospheric circulation, the atmospheric carbon cycle, marine–atmosphere circulation, and aerosol activities. Aerosols play a key role in climate change and air quality because of its direct, semi-direct, and indirect effects on the radiation budget. As the most important anthropogenic greenhouse gas, carbon dioxide plays a key role in climate studies and for environment monitoring. The European Space Agency (ESA) developed the Aeolus mission to provide global profiles of wind, clouds and aerosols properties. Aeolus carries the first wind lidar in space (ALADIN) and was successfully launched in August 2018. The lidar mission ACDL (Aerosol and Carbon dioxide Detection Lidar) implemented by China is currently scheduled for launch in 2021 to measure CO₂ and aerosol from space. The activities of the project aim at validating Aeolus, the study of long-range transport of aerosol, and the preparation of the Chinese CO₂ spaceborne lidar mission. The first objective is to validate Aeolus wind products based on ground-based and airborne wind lidar observations, and is undertaken by DLR (Deutsches Zentrum f. Luft- und Raumfahrt) and OUC (Ocean University of China). The second objective is to carry out the preparation of ACDL through ground-based and airborne lidar observations by CAS-SIOM (Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences), building on the experience made with the validation of Aeolus. The third objective is to study the long-range dust transport, based on ground-based and satellite lidar observations, by OUC.

Already within the first weeks after the launch of ESA´s Earth Explorer mission Aeolus on 22 August 2018, the first atmospheric backscatter measurements and wind profiles were obtained on 5 and 12 September 2018, respectively. This swift availability of observations from ALADIN after launch is considered as a great success for ESA, space industry as well as the algorithm and processor developer teams that had been working together for more than 15 years before launch. This cooperation from the pre-launch phase of Aeolus was extended within a new framework for exploitation activities named Data Innovation and Science Cluster (DISC) and started in January 2019. The Aeolus instrument performance wrt. random and systematic errors for the wind products were assessed by the Aeolus DISC using the numerical weather prediction (NWP) model from the European Centre for Medium-Range Weather Forecasts (ECMWF). In addition, a number of airborne and ground-based validation campaigns were performed for assessing the wind and aerosol product quality by means of collocated observations. DLR performed 3 airborne validation campaigns since the launch of Aeolus with the DLR Falcon 20 aircraft which was equipped with the airborne demonstrator of Aeolus (A2D) and a 2-µm Doppler lidar as a wind reference instrument. The first two campaigns took place in Central Europe and the third one in the region of the North Atlantic around Iceland and Greenland, delivering a comprehensive dataset to be used for the validation of the Aeolus wind product quality. The aim of the Aeolus mission is to provide global observations of vertical profiles of one component of the horizontal wind vector with sufficient accuracy and precision to demonstrate a positive impact on NWP analysis and forecasts. Impact experiments using the ECMWF model show a significant positive impact of Aeolus on the analysis and weather forecast. Today Aeolus observations are used operationally by several NWP centres including ECMWF, German Weather Service (DWD), Météo-France and UK Met Office.

To validate the data products of Aeolus and to varify the measurement principles of ACDL, the following activities are carried out from China side. Ground-based WACAL (WAter vapor, Cloud and Aerosol Lidar) was developed by the lidar group at OUC (Ocean University of China) and deployed during several field campaigns, including the third Tibetan Plateau Experiment of Atmospheric Sciences (TIPEX III) in Naqu (31.5°N, 92.05°E) with a mean elevation of more than 4500 m above MSL in summer of 2014. For validation of Aeolus wind HLOS data products, CDLs (Coherent Doppler Wind Lidars) developed by OUC were also deployed at 17 observation stations in the coastal zone and China Seas for long-term simultaneous observations with Aeolus. The CAL/VAL campaign contributes to exploit the Aeolus wind observations for the study of atmospheric dynamics. As the science application, a long-term large-scale Sahara dust transport event occurred during 14 June and 27 June 2020 is tracked with the spaceborne lidars ALADIN and CALIOP observations and the models ECMWF and HYSPLIT analysis. During 9 and 19 March 2019, an IPDA CO₂ lidar airborne demostrator was mounted on an aircraft to perform the observation of CO₂. The simultaneous ground-based lidars, Fourier Transform infrared Spectrometer (FTS) and sun photometers are emplored for the validation of CO₂ lidar airborne demostrator. Accordingly, the calibration and retrieval method for aerosol optical properties with CDL are developed with the co-located sun photometer measurements.