ALBERT

Description: The Geoengineering Model Intercomparison Project (GeoMIP) is a coordinating framework, started in 2010, that includes a series of standardized climate model experiments aimed at understanding the physical processes and projected impacts of solar geoengineering. Numerous experiments have been conducted, and numerous more have been proposed as “test-bed” experiments, spanning a variety of geoengineering techniques aimed at modifying the planetary radiation budget: stratospheric aerosol injection, marine cloud brightening, surface albedo modification, cirrus cloud thinning, and sunshade mirrors. To date, more than 100 studies have been published that used results from GeoMIP simulations. Here we provide a critical assessment of GeoMIP and its experiments. We discuss its successes and missed opportunities, for instance in terms of which experiments elicited more interest from the scientific community and which did not, and the potential reasons why that happened. We also discuss the knowledge that GeoMIP has contributed to the field of geoengineering research and climate science as a whole: what have we learned in terms of intermodel differences, robustness of the projected outcomes for specific geoengineering methods, and future areas of model development that would be necessary in the future? We also offer multiple examples of cases where GeoMIP experiments were fundamental for international assessments of climate change. Finally, we provide a series of recommendations, regarding both future experiments and more general activities, with the goal of continuously deepening our understanding of the effects of potential geoengineering approaches and reducing uncertainties in climate outcomes, important for assessing wider impacts on societies and ecosystems. In doing so, we refine the purpose of GeoMIP and outline a series of criteria whereby GeoMIP can best serve its participants, stakeholders, and the broader science community.

Description: As one of the seafloor geodetic techniques, precise seafloor positioning by the GNSS—Acoustic ranging combination technique (GNSS-A) is applied for the observations of the crustal deformation in the plate subduction zones (e.g., Spiess et al., 1998; Fujita et al., 2006). For the precise positioning with the GNSS-A, it is required to appropriately cancel or correct the effects of sound speed variation on acoustic travel time. We have developed static GNSS-A analysis methods where the sound speed effects were simultaneously corrected with well-distributed acoustic data, by introducing the perturbation field model (Watanabe et al., 2020). Based on the empirical Bayes approach, it was implemented in an open-source software GARPOS (the latest version is v1.0.1, https://doi.org/10.5281/zenodo.6414642), in which hyperparameters are selected to minimize the Akaike Bayesian Information Criterion (ABIC; Akaike, 1980). Watanabe et al. (under review, preprint https://doi.org/10.21203/rs.3.rs-1881756/v1) developed the upgraded version of GARPOS, i.e., GARPOS-MCMC (the latest version is v1.0.0, https://doi.org/10.5281/zenodo.6825238), with a full-Bayes GNSS-A analysis scheme, where the hyperparameters are also expressed as probability density functions. The parameters are estimated with the Markov chain Monte Carlo method, which enabled us to directly sample from the joint posterior of parameters including any hyperparameters and evaluate the correlations between those parameters. However, it requires computational resources as the number of acoustic data becomes large. To overcome the disadvantage, we introduced the widely applicable Bayesian information criterion (WBIC; Watanabe, 2013) for model selection for some hyperparameters, to partly take an empirical Bayes approach, and implemented it on GARPOS-MCMC.

Description: Effects of mid-latitude Sea Surface Temperature (SST) fronts on the middle atmosphere were investigated by using the high-top MIROC AGCM. This model has horizontal and vertical resolutions of ~120km and 550 m, respectively, with model top of ~95 km. Non-orographic gravity wave parameterizations were not included. We have conducted two idealized experiments. One used the SST with realistic meridional gradients (control run), and the other did the SST with smoothing meridional gradients of mid-latitude SST front (no SST front run; NF run), similar to the previous study (e.g., Nakamura et al. 2008). Previous numerical experiments showed that mid-latitude SST fronts affect precipitation, heat fluxes, and baroclinic wave activities in the troposphere. Our model experiments further showed that more gravity waves were generated around baroclinic waves in the control run than the NF run, which propagate into the stratosphere and mesosphere. Wave momentum fluxes associated with these gravity waves are larger from the upper troposphere to ~0.03 hPa, resulting in larger westward forcing in the control run. Amplitudes of gravity waves in the NF run were smaller than those in the control run, and these waves tend to be dissipated at higher altitudes. Shapes of the zonal mean zonal winds including polar night jets are more realistic in the control run, indicating the SST fronts have impact on not only the troposphere but also on the middle atmosphere.

Description: To investigate this question, we first prepared a new model (Model A) and a model using the previous cumulus parameterization (Model B), each tuned to obtain as realistic a QBO as possible. Each of these models has a different equatorial tropospheric circulation. We then conducted an experiment to nudge the tropospheric circulation of these models using ERA5 daily mean horizontal winds. Surprisingly contrasting results were obtained. Tropospheric nudging resulted in a QBO cycle of 39 months for model A instead of 28 months. The QBO period for Model B remained almost the same, with a slight improvement in the QBO amplitude in the lower stratosphere. This suggests that the equatorial tropospheric circulation bias in Model A is significant. We examined the bias in the upper Walker circulation in Model A and found that the easterly winds in the eastern hemisphere during June-September are stronger than observed and extend eastward and westward. Analysis using 3D wave activity fluxes revealed that the momentum fluxes associated with atmospheric waves propagating eastward and upward in the QBO easterlies and reaching the QBO westerly shear, and the eastward acceleration caused by their convergence, are excessive, reflecting the bias. The increase in the QBO period in the experiment with nudging tropospheric circulation was due to the elimination of these biases, which resulted in a lack of driving force for the QBO that had originally been tuned to the observed QBO period. Further tuning is required to answer the question.

Description: Although GNSS-A (Global Navigation Satellite System–Acoustic ranging combination technique) observation is a technology that measures steady or sudden seafloor crustal deformations at the centimeter level, the technical capabilities are inferior to those of terrestrial GNSS observation in terms of accuracy and frequency. Therefore, many technological developments are currently underway. We are conducting error factor analysis through simulation and experimental research in order to improve the observation accuracy and frequency of SGO-A, which is operated by the Japan Coast Guard. By investigating the effects of high-rate GNSS on GNSS-A, development of representation and modeling methods of underwater sound speed fields, and equipment and angle-dependent characteristics due to sonar characteristics, we are progressing in developing quantitative evaluation and correction methods for errors. The accuracy research of GNSS-A is closely related to the accuracy research of GNSS. In the near future, we would like to construct a unified error correction method for instruments and observation envirnments, similar to GNSS. Regarding the observation frequency, we have reached the limit of observation frequency using ships around 2020, and the development of new sea surface platforms is necessary. For example, research on autonomous buoys (wave glider), moored buoys, and flying-boat type UAVs is underway. Various marine engineering applications other than GNSS-A are underway for a research field of sea surface platforms, and this field may be further updated in the future. In this presentation, we will also discuss new sea surface platforms for GNSS-A.

Description: Around the Japanese Islands, major subduction zones along the plate boundaries of the Pacific Plate and the Philippine Sea Plate have repeatedly caused megathrust earthquakes. GNSS-Acoustic ranging combination technique (GNSS-A) is an effective tool to measure the absolute position on the seafloor, from which we can visualize the plate boundary conditions at these subduction zones. The Japan Coast Guard has been conducting GNSS-A observations at the sites deployed along the Japan Trench and the Nankai Trough, named the Seafloor Geodetic Observation Array (SGO-A). At the SGO-A sites, we have been periodically conducting campaign observations for approximately 20 years. In these two decades, technological advancements in our observation and analysis techniques have enabled us to detect shallow slow slip events lasting for a year (Yokota and Ishikawa 2020). Our decadal observations have revealed the processes related to the 2011 Tohoku-oki Earthquake (Watanabe et al. 2021). We have also been developing a csv-based data format for GNSS-A observation data, which we have been discussing in a working group of the Inter-commission Committee on Marine Geodesy (ICCM) of the International Association of Geodesy (IAG).