We use satellite measurements and high-resolution models to study the anomalies in water vapor, temperature, and cloud in the upper troposphere and lower stratosphere (UTLS) region induced by the deep and overshooting convections. A "cloud-assisted" retrieval method is developed to use nadir infrared hyperspectral measurements to retrieve the thermodynamical profiles near and above the convective clouds, filling the vacuum of these data in this critical region. Applying this method to the A-Train satellite measurements, we have obtained a dataset quantifying the thermodynamical anomalies above tropical cyclones, which discloses interesting temperature and humidity anomalies right above the convective clouds and allows us to identify radiative heating signatures of different types of underlying clouds. On the other hand, we use a high-resolution NWP model, capable of simulating the gravity waves and their breaking process in the UTLS caused by overshooting convections, to analyze the impacts of overshooting convection on the UTLS and characterize the properties of water vapor and humidity anomalies, which presents a simulated "truth" for testing the retrievability of these thermodynamic anomalies by new satellite instruments. This analysis highlights a critical lack and need of "curtain-views" of the water vapor and temperature measurements to accompany similar cloud profiles in studying the cloud physics, convective impacts and climate trends in the UTLS region.

GNSS radio occultation (RO) measurements have sensitivity to tropospheric humidity and the radio occultation method therefore has the potential to provide essential knowledge about distribution of humidity in the troposphere. Since the radio occultation technology provides products with reference data quality the method also holds a promise to give estimates of water vapour trends on the time scale of multiple decades, as the radio occultation based climate data records continue to grow.

The tropospheric radio occultation measurand, refractivity, is a combination of a temperature component and a humidity component. These two components cannot be estimated individually without using prior knowledge. A one-dimensional variational procedure (1D-Var) is applied for this purpose, in which NWP model forecast data is used as background for temperature and humidity retrieval. The goal is eventually to be able to positively attribute possible trends and features detected in tropospheric humidity to the radio occultation measurement itself, with negligible interference from model data.

The first step towards that goal is to establish estimates of the observation and background uncertainties and error correlations. This is being done by using empirical methods where independent collocated data sets are analysed and used for estimating random and systematic uncertainties. The second step, which is yet to be explored, is to perform a de-trending operation on the background data before a reprocessing of the radio occultation 1D-Var data sets is carried out. Based on this, the third step is to generate and validate multi-mission radio occultation climate data records, corrected for sampling errors. This presentation discusses reprocessed data records generated by the EUMETSAT ROM SAF (Radio Occultation Meteorology Satellite Application Facility) and will focus on the roadmap to achieve a new radio occultation based water vapour climate data record.

Water vapour is a key component of the Earth climate system. In the lowest 100 m - 1 km region, referred to as the Planetary Boundary Layer (PBL), plays a crucial role in the energy and water cycles by mediating the exchange of heat, momentum, water, and chemical exchange constituents and aerosols. Not only acting as a source for the development of precipitation, water vapour in the PBL also plays a critical role in the evolution of low cloud cover, which has a fundamental role in tropical/subtropical circulation. In turn, these interactions have a strong impact on the Earth’s radiation budget. With land surface temperatures warming at a faster rate relative to the ocean, near-surface/PBL continental absolute water vapour concentrations have increased while having a lower relative humidity. Although an essential quantity for climate, most near-surface/PBL observations (absolute & relative) humidity come from in situ measurements. While there have been extensive efforts in characterising near-surface humidity, there are only a few independent dedicated PBL water vapour records.
Our previous study, Trent et al. 2018, demonstrated the ability to retrieve bulk estimates of PBL water vapour (see Figure 1) from the Greenhouse Gases Observing Satellite (GOSAT) with an accuracy of 5%. In this study we present three new innovations: i) updates to the algorithm to include stable water vapour isotopologues, ii) first decadal analysis of satellite PBL water vapour over land, and iii) linking PBL water vapour to surface humidity from the UK Met Office HadISDH climate data record. With a second GOSAT launched in 2018 and a third planned for 2023, this new climate data record could span nearly 30 years. Additionally, we will also discuss the potential of GOSAT PBL water vapour to provide insights into the potential of Sentinel 5 which will operate on the MetOp-SG platform from 2024.

Water vapour is the single most important natural greenhouse gas in the atmosphere, thereby constraining the Earth’s energy balance, and is also a key component of the water cycle. There is consequently the need to consolidate our knowledge of natural variability and past changes in water vapour and to establish climate data records (CDRs) of both total column and vertically resolved water vapour for use in climate research. This was and will be the objective of the ESA Water Vapour Climate Change Initiative (WV_cci) project.
Within WV_cci a global total column water vapour (TCWV) data record was generated by combining microwave and near-infrared imager based TCWV over the ice-free ocean as well as over land, coastal ocean and sea-ice, respectively. The data record relies on microwave observations from SSM/I, SSMIS, AMSR-E and TMI, partly based on a fundamental climate data record (EUMETSAT CM SAF edition 3) and on near-infrared observations from MERIS (3rd reprocessing), MODIS-Terra (collection 6.1) and OLCI (1st reprocessing). Details of the retrieval are described in the literature. Both, the microwave and near-infrared data streams are processed independently and combined afterwards by not changing the individual TCWV values and their uncertainties. The data records were combined within ESA WV_cci and will be released via EUMETSAT CM SAF in early 2022.
This presentation will briefly introduce the global TCWV product and then has two foci: first, results from validation and comparison to various other data records will be shown. Second, results from example applications will be shown. This will include first results from comparisons to CMIP6 and utilisation in context of atmospheric rivers analysis.

Climate models have continuously been developed and improved over the last decades, yet, accurately reproducing observed climate remains challenging for these numerical models. Therefore, it is important to routinely monitor how well the models reproduce the observed past climate and to systematically analyze, evaluate, and document their results to improve our understanding of the relevant physical mechanisms and climate feedbacks. The Earth System Model Evaluation Tool (ESMValTool) has been developed to take model evaluation to the next level by facilitating analysis of many different earth system model components, providing well-documented source code and scientific background of implemented diagnostics and metrics and allowing for traceability and reproducibility of results. It is developed by a lively and growing community continuously improving the tool supported by multiple national and European projects.
Due to its importance for the radiation budget of the atmosphere as the most important natural greenhouse gas and its key role in the hydrological cycle, water vapour is of great importance for Earth’s climate. Evaluation of water vapour in Earth system models is therefore an important step in assessing the robustness of model projections. This presentation gives an overview on the scientific diagnostics and metrics of the ESMValTool, which are used to evaluate atmospheric water vapour from models contributing to the Coupled Model Intercomparison Project Phase 6 (CMIP6) with observational data sets. These data sets include water vapour products retrieved from satellite measurements like RSS (Remote sensing system) microwave radiometer data, ESA-CCI (Climate Change Initiative) water vapour, and SWOOSH (Stratospheric Water and Ozone Satellite Homogenized). Here, we focus on the evaluation of the short wave radiative transfer in Earth system models based on observations of total column water vapour and radiative fluxes, as well as comparison of the trends and the shape of the vertical profiles of water vapour.