Description: As the result of changes in ice dynamics and weather-driven changes on the surface, surface elevation changes over ice sheets are sensitive to climate forcing. Thus, long-term surface elevation changes over ice sheets of Greenland and Antarctica are of essential to assess the impact of climate change. Here, a dataset of monthly surface elevation time series over ice sheets of Greenland and Antarctica at 5km grid resolution using ERS-1, ERS-2, Envisat, and CryoSat-2 radar altimeter observations from August 1991 to December 2020. An updated plane-fitting least-squares regression strategy and Empirical orthogonal function (EOF) reconstruction were applied to ensure the accuracy and self-consistency of the merged elevation time series in the data processing. In addition, the cross-comparison with the IceBridge airborne laser altimeter observations confirmed that our merged dataset is reliable. Benefiting from its high temporal and spatial resolutions, the evolution processes on multiple temporal (up to 30 years) of ice loss from the main outflow glaciers in Greenland and Antarctica can be derived in detail. The spatiotemporal patterns of accelerating or decelerating surface elevation changes over ice sheet related to ENSO (for the Antarctic Ice sheet) and NAO (for the Greenland Ice sheet) indicated that climate forcing shifts oceanic forcing or atmospheric forcing in some way to affect ice sheet changes. Our merged time series provide a vital dataset for exploring the processes of climate forcing driving ice sheet change.

Description: A severe flooding hit the region of central east China to southern Japan in summer 2020. It is found that the extremely strong rainfall experienced pronounced subseasonal variation, dominated by a quasi-biweekly oscillation (QBWO) mode. The analysis of streamfunction of water vapor flux demonstrates that a large amount of water vapor eastward zonal transport from the Bay of Bengal and Indo-China and northward transport from the South China Sea provided the background moisture supply for the rainfall. The quasi-biweekly anomalies of potential and divergent component of vertically integrated water vapor flux played an important role in maintaining the subseasonal variability of extreme rainfall. The diagnosis of moisture tendency budget shows that the enhanced moisture closely related to the quasi-biweekly fluctuated rainfall was primarily attributed to the moisture convergence. Further analysis of time-scale decomposition in the moisture convergence indicates that the convergence of background mean specific humidity by the QBWO flow and convergence of QBWO specific humidity by the mean flow played dominant roles in contributing to the positive moisture tendency. In combination with adiabatic ascent over the rainfall region induced by the warm temperature advection, the boundary layer moisture convergence strengthened the upward transport of water vapor to moisten the middle troposphere, favoring the persistence of rainfall. The vertical moisture transport associated with boundary layer convergence was of critical importance in causing low-level tropospheric moistening.

Description: The East Asian winter monsoon (EAWM) exerts impacts on climate in the regions from East Asia down to the Maritime Continent. The El Niño-Southern Oscillation (ENSO) affects not only the tropical climate, but also the extratropical climate. This study evaluates the relationship between El Niño-Southern Oscillation (ENSO) and the East Asian winter monsoon (EAWM) in 26 Coupled Model Intercomparison Project phase 6 (CMIP6) models. Results show that the model’s ability of simulating the ENSO-EAWM relationship is more dependent upon the longitudinal extension of ENSO-related equatorial Pacific sea surface temperature (SST) anomalies than the amplitude of the equatorial central-eastern Pacific SST anomalies. The influence of the amplitude of ENSO on the simulation of the ENSO-EAWM relationship depends on the westward extension of ENSO-related equatorial Pacific SST anomalies. Another factor for the model’s ability of simulating the ENSO-EAWM relationship is the SST anomalies in the tropical western North Pacific (WNP). A westward extension of the equatorial Pacific SST anomalies shifts the west branch of anomalous Walker circulation too far westward, which causes westward displaced anomalous ascending (descending) motion around the Philippine Sea through modulating regional meridional vertical circulation in El Niño (La Niña) years. The weak SST anomalies in the tropical WNP lead to the failure of inducing anomalous lower-level anticyclone (cyclone) over the Philippine Sea through a Rossby wave response in El Niño (La Niña) years. The accompanying weak anomalous lower-level southwesterly (northeasterly) winds along the west flank of the anomalous anticyclone (cyclone) account for the weak ENSO-EAWM relationship.

Description: An open-ocean polynya is an offshore area where the sea ice is significantly less than that of its surrounding area. Polynyas are known as oases in Antarctic for driving the interactions between the atmosphere and the ocean. Extensive studies have addressed the characteristics and mechanisms of open-ocean polynyas in the Weddell and Cosmonaut Seas. The purpose of this study is to indicate the existence of more persistent open-ocean polynyas in the Cooperation Sea and propose the atmospheric and oceanic forcing mechanisms responsible for the formation of the open-ocean polynyas. Our results offer a more complete circumpolar view of open-ocean polynyas in the Southern Ocean and have implications for physical, biological, and biogeochemical studies of the Southern Ocean. Future efforts should be particularly devoted to more extensively observing the ocean circulation to understand the variability of open-ocean polynyas in the Cooperation Sea.

Description: The bathymetry around Antarctica can govern the shelf sea circulations and play a key role in conditioning water masses. In Prydz Bay, the Prydz Bay Gyre and coastal currents are also determined by the continental shelf topography. However, due to the paucity of beam echo sounding data, the bathymetric datasets in Prydz Bay still have large uncertainties. With the aid of in situ hydrographic observations, this study focuses on the correction of an up-to-date bathymetric dataset and the resultant influences on the shelf circulation and the basal melting of the ice shelves. The corrected bathymetry mainly improves the biased shallow representations in the uncorrected bathymetric data set, with a maximum change of ~500 m deepening in the eastern flank of Prydz Bay. Sensitivity numerical experiments show that the bathymetric corrections in Prydz Bay have a significant impact on the circulation pattern and onshore warm water intrusions. In addition, the corrected bathymetry markedly decreases the heat transport towards the calving front of the Amery Ice Shelf. The onshore heat transport reduces by ~22.18% from ~5.23×10〈sup〉13〈/sup〉 J s〈sup〉-1〈/sup〉 to ~4.07×10〈sup〉13〈/sup〉 J s〈sup〉-1〈/sup〉 over the outer shelf. Over the inner shelf, the heat transport towards the Amery Ice Shelf reduces by ~18.15% from ~5.95×10〈sup〉13〈/sup〉 J s〈sup〉-1 〈/sup〉to ~4.87×10〈sup〉13〈/sup〉 J s〈sup〉-1〈/sup〉. Consequently, the temporally and spatially averaged basal melting rate of the Amery Ice Shelf reduces by ~13.04% from ~0.69 m yr〈sup〉-1〈/sup〉 to ~0.60 m yr〈sup〉-1〈/sup〉.

Description: Numerous studies have indicated that the atmospheric heat source (AHS) over the Tibetan Plateau (TP) is highly correlated with the western North Pacific anomalous anticyclone (WNPAC) in summer. However, such an interannual relationship has been weakened since the late 1990s. The present work shows that the TP AHS was significantly and positively correlated with the WNPAC in 1979–1999 (P1), while this relationship became insignificant hereafter (2000–2020; P2). We identify that the long-term change in the upper-level atmospheric circulation over the TP is responsible for weakening the relationship. An obvious upper-level anticyclonic trend occurred over the northeastern TP in the past four decades, with an easterly trend on the anticyclone’s southern flank, representing anomalous westerlies during P1 but anomalous easterlies during P2 over the main portion of the TP. With the anomalous upper-level westerlies in P1, the abnormal high pressure induced by the TP heating (i.e. AHS) extended downstream in the upper troposphere. Subsequently, anomalous descending motions formed over the northwestern Pacific due to the eastward-extended high pressure, together with the vertical transport of negative relative vorticity, favorable for the enhancement of the WNPAC. Whereas in P2, the TP heating-induced abnormal high pressure was confined over the southern TP due to the anomalous easterlies, suppressing its downstream influence and finally breaking the connection between the TP AHS and the WNPAC. Modeling results from both LBM sensitivity experiments and CESM large ensemble dataset further confirm the important role of the change in background circulation in weakening the relationship.

Description: Recent annual assessments of present-day and future climate variability provided by the World Meteorological Organization have motivated the need for the attribution of environmental change, separating climate forcing agents from large-scale natural climate variability. To address this need operational forecasting systems are essential together with sustained, comprehensive and relevant observations for assessing current climate and climate forcers. The World Climate Research Programme Light House Activity – Explaining and Predicting Earth System Change (EPESC) – will cast a new light on the proximal drivers of regional climate variation on annual-to-decadal (A2D) timescales. The EPESC is focused on three distinct yet interrelated themes: The monitoring and modelling of Earth system change; the integrated attribution, prediction and projection of A2D changes including the potential for extremes; and the assessment of current and future hazards. In this presentation we will outline the current and future requirements of A2D prediction and projection, including the requisite infrastructure of operational attribution and the need for comprehensive whole-atmosphere observations, such as those which will be provided by the proposed Changing-Atmosphere Infra-Red Tomography Explorer (CAIRT), recently selected by the European Space Agency (ESA) as one of four candidates for the Earth Explorer 11 mission.

Description: Due to different reanalysis methods and input data, there exist big discrepancies between hydrological models from regions to regions. Therefore, accuracy assessment of different models is necessary before applications in specific areas. In this report, six hydrological models, including GLDAS, FLDAS, ERA5, MERRA-Land, NCEP and WGHM were evaluated and analyzed through inter-comparison between models and outer-comparison with Global Positioning System (GPS) station height time series, GRACE/GRACE-FO RL06 Mascon solutions, and Precipitation data from Global Precipitation Climatology Centre (CPCC) for a comprehensive assessment of model differences. We then try to combine the six models through variance component estimation (VCE), entropy weight method (EWF), coefficient of variation method (CVM) and other mathematical models, so as to improve the accuracy, integrity and applicability of hydrological models. Our results show that the root mean square (RMS) of global GPS height time series improves by up to 17% after correcting the hydrological effect obtained from combined models compared with that from individual models, while the correlation with rainfall also improves by 30% at most. Compared with TWSC derived from satellite gravity inversion, the correlation coefficient increases from 0.2 to 0.8 at the highest. Finally, the combined methods exhibit much higher signal-to-noise ratio (SNR) value than that of the pre-combined models, and the VCE combined model performs as the optimal hydrology model to correct the GPS height. Therefore, we conclude that the combined hydrological model could provide a better data source for monitoring hydrological changes and surface load deformation at a global scale.

Description: Ocean surface winds are critical for shaping the Earth's weather and climate, and the CYGNSS mission, launched in 2016, is designed to monitor ocean wind. This study presents a novel deep learning model, CNN-LSTM, which retrieves ocean wind speed using CYGNSS observations. The model uses a Convolutional Neural Network (CNN) module to extract spatial features from a two-dimensional matrix of the delay-Doppler Map (DDM) around the Specular Point (SP) and a Long Short-Term Memory (LSTM) module to capture temporal features from a time series. The model's performance is evaluated against the fifth generation European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis (ERA5) products, and error analysis is performed to demonstrate the model's robustness at both spatial and temporal scales. Additionally, the study proposes the segmental modeling and calibration to address the issue of wind speed underestimation at high wind speeds. The study demonstrates the effectiveness and feasibility of the CNN-LSTM model in providing efficient processing of GNSS reflectometry observations and accurate global-scale ocean wind speed retrieval.

Description: Ice shelf basal melting is the major cause of the current mass loss of Antarctic ice sheets. The resultant meltwater plumes contribute to the development of the unique two-layer stratified ice shelf–ocean boundary currents underlain by warmer, saltier, and stationary source waters. However, knowledge of the thermodynamics within these plumes, controlling the heat available for melting ice, remains outstanding. To this end, we investigated that important issue by developing a 2.5-dimensional nonhydrostatic vertical slice model with 1.5 m vertical resolution, and conducted the reference run based on a representative Ice Shelf Water (ISW)-High Salinity Shelf Water (HSSW) boundary current beneath the Amery Ice Shelf, East Antarctica. Based on that we identified two dominating vertical thermal processes regulating the local temperature: the turbulent diffusion and the shear instabilities-induced convection, and carried out a quantitative thermal budget analysis in the framework of plume model, including deriving an analytical expression for the entrainment-induced heat flux. Moreover, after evaluating the entrainment parametrizations, we found that the common assumption of neglecting the velocity at the lower boundary of meltwater plume potentially leads to a considerable deviation from the real entrainment. The sensitivity of the simulated results to model configuration and model resolution are also investigated. The findings in this study imply that we need to improve the model resolution of current ocean cavity models to sufficiently resolve the interfacial processes between lighter–denser waters.