Development and Evaluation of an Ensemble-Based Data Assimilation System for Regional Reanalysis Over the Tibetan Plateau and Surrounding Regions.

The Tibetan Plateau is regarded as the Earth's Third Pole, which is the source region of several major rivers that impact more 20% the world population. This high-altitude region is reported to have been undergoing much greater rate of weather changes under global warming, but the existing reanalysis products are inadequate for depicting the state of the atmosphere, particularly with regard to the amount of precipitation and its diurnal cycle. An ensemble Kalman filter (EnKF) data assimilation system based on the limited-area Weather Research and Forecasting (WRF) model was evaluated for use in developing a regional reanalysis over the Tibetan Plateau and the surrounding regions. A 3-month prototype reanalysis over the summer months (June-August) of 2015 using WRF-EnKF at a 30-km grid spacing to assimilate nonradiance observations from the Global Telecommunications System was developed and evaluated against independent sounding and satellite observations in comparison to the ERA-Interim and fifth European Centre for Medium-Range Weather Forecasts Reanalysis (ERA5) global reanalysis. Results showed that both the posterior analysis and the subsequent 6- to 12-hr WRF forecasts of the prototype regional reanalysis compared favorably with independent sounding observations, satellite-based precipitation versus those from ERA-Interim and ERA5 during the same period. In particular, the prototype regional reanalysis had clear advantages over the global reanalyses of ERA-Interim and ERA5 in the analysis accuracy of atmospheric humidity, as well as in the subsequent downscale-simulated precipitation intensity, spatial distribution, diurnal evolution, and extreme occurrence.

Separation of air components and pollutants by the Earth's gravitational field.

In this work, we develop a model able to predict the equilibrium separation of gases due to differences in their molecular weights and the action of gravity. The separation of H, He, O, and N2 with altitude is a characteristic phenomenon of the heterosphere. The model is able to qualitatively recreate the compositional profile of the whole heterosphere from a single composition measurement. The model is applied to the separation of air components and pollutants by empty wells drilled on the planet surface. It predicts that the separation of gases would be possible in wells deep enough under equilibrium. The high molecular weight of some anthropogenic pollutants (SO2, O3, NO2, CO2, etc.) would facilitate their segregation along shorter distances compared to those involved in the heterosphere. The simulations indicate that deep wells could concentrate some air components and pollutants by orders of magnitude over the levels at the Earth's surface without external energy input. For instance, argon molar fractions of >40% and >60% could be achievable at 44 km and 55 km depth, respectively. Finally, we discuss the feasibility of gravitational separation as a potential pollution abatement technology.