Dependence of the radiative-convective equilibrium structure of the lower atmosphere of Venus on the specification of an atmospheric thermodynamic model is investigated. A series of thermodynamic models including ideal gases, van der Waals gases, and real gases are introduced by the use of the Helmholtz energy given by the EOS-CG mixture model (EOS-CG: Equation of State for Combustion Gases and Combustion Gas-like Mixtures). It is demonstrated that the radiative-convective equilibrium profile for the real gas differs significantly from that for the ideal gas with temperature-dependent specific heat by an increase of about 7 K in the surface temperature. This difference is caused by the fact that the adiabatic lapse rate evaluated with the thermodynamic model of real gas is larger than that of ideal gas, since the non-ideality of gas increases the thermal expansion coefficient, which overwhelms the increases in density and specific heat. It is confirmed that, in order to obtain better calculations of atmospheric circulations including the lower atmosphere of Venus, the ideal gas with a constant specific heat should be abandoned. The ideal gas with a temperature-dependent specific heat may not be enough. A promising method is to use the ideal gas but with the temperature-dependent specific heat such that its adiabatic lapse rate profile mimics that for the real gas.

To determine the complex refractive indices of aerosol particles in the atmospheric boundary layer, simultaneous measurements of scattering coefficients at 450, 550, and 700 nm wavelengths, absorption coefficient at 565 nm, and aerosol particle number size distributions were performed during a voyage of the icebreaker Shirase from Tokyo to the offing of the Philippines over the northwestern Pacific in November 2010. Three sets of Ångström exponents were calculated using the three observed scattering coefficients. Using the observed number size distributions, three sets of Ångström exponents were reproduced by assuming their complex refractive indices. Appropriate complex refractive indices for aerosol particles in the atmospheric boundary layer can be obtained when the difference between the observed and reproduced Ångström exponents is minimal. Absorbing substances were assumed to be present in the fine particles. For polluted air masses, if the refractive index for aerosol particles was uniform regardless of the particle size, the estimated Ångström exponents were consistent with the observed values. The refractive index must be the normal dispersion, which increases with a decrease in wavelength. For pristine air masses, the refractive index was estimated to be higher for coarse particles than for fine particles. This could be explained by preferential condensation of organic compounds onto coarse particles, which is observed to alter the number size distribution over Chichi-jima of the Ogasawara Islands in the northwestern Pacific in August 2014 and February 2015. This study is the first to report that the increase in the refractive index of coarse particles is likely caused by the optical properties of volatile organic compounds and/or secondary organic aerosols condensed on coarse particles.

It is well-known in rainfall ensemble forecasts that ensemble means suffer substantially from the diffusion effect resulting from the averaging operator. Therefore, ensemble means are rarely used in practice. The use of the arithmetic average to compute ensemble means is equivalent to the definition of ensemble means as centers of mass or barycenters of all ensemble members where each ensemble member is considered as a point in a high-dimensional Euclidean space. This study uses the limitation of ensemble means as evidence to support the viewpoint that the geometry of rainfall distributions is not the familiar Euclidean space, but a different space. The rigorously mathematical theory underlying this space has already been developed in the theory of optimal transport (OT) with various applications in data science.

In the theory of OT, all distributions are required to have the same total mass. This requirement is rarely satisfied in rainfall ensemble forecasts. We, therefore, develop the geometry of rainfall distributions from an extension of OT called unbalanced OT. This geometry is associated with the Gaussian-Hellinger (GH) distance, defined as the optimal cost to push a source distribution to a destination distribution with penalties on the mass discrepancy between mass transportation and original mass distributions. Applications of the new geometry of rainfall distributions in practice are enabled by the fast and scalable Sinkhorn-Knopp algorithms, in which GH distances or GH barycenters can be approximated in real-time. In the new geometry, ensemble means are identified with GH barycenters, and the diffusion effect, as in the case of arithmetic means, is avoided. New ensemble means being placed side-by-side with deterministic forecasts provide useful information for forecasters in decision-making.

The Japan Meteorological Agency (JMA) has developed the third Japanese global atmospheric reanalysis, the Japanese Reanalysis for Three Quarters of a Century (JRA-3Q). The objective of JRA-3Q is to improve quality in terms of issues identified in the previous Japanese 55-year Reanalysis (JRA-55) and to extend the reanalysis period further into the past. JRA-3Q is based on the TL479 version of the JMA global Numerical Weather Prediction (NWP) system as of December 2018 and uses results of developments in the operational NWP system, boundary conditions, and forcing fields achieved at JMA since JRA-55. It covers the period from September 1947, when Typhoon Kathleen brought severe flood damage to Japan, and uses rescued historical observations to extend its analyses backwards in time about 10 years earlier than JRA-55. This paper describes the data assimilation system, forecast model, observations, boundary conditions, and forcing fields used to produce JRA-3Q as well as the basic characteristics of the JRA-3Q product. The initial quality evaluation revealed major improvements from JRA-55 in the global energy budget and representation of tropical cyclones (TCs). One of the major problems in JRA-55—global energy imbalance with excess upward net energy flux at the top of the atmosphere and at the surface—has been significantly reduced in JRA-3Q. Another problem—a trend of artificial weakening of TCs—has been resolved through the use of a method that generates TC bogus based on the JMA operational system. There remain several problems such that the volcanic-induced stratospheric warming is smaller than expected. This paper discusses the causes of such problems and possible solutions in future reanalyses.

Sea surface temperature anomaly (SSTA) in the Kuroshio region near the East China Sea (K-ECS) during August has been found to be closely related to the September precipitation anomaly over Central China (CC) in this study. The significant causality is identified from SSTA in K-ECS to anomalous rainfall over CC. When a negative SSTA occurs in K-ECS during August, its cooling effect on the overlying atmosphere lasting from August to September promotes the formation of anomalous anticyclonic circulation below 600 hPa above K-ECS and the southeast of China by weakening the local convection. The southerly in the west of this anomalous circulation transports more water vapor into CC. Eventually, the convergence of moisture provides favorable conditions for the generation of precipitation here. The responsive characteristics of the anomalous atmospheric circulation during September to a negative SSTA in K-ECS in August can be confirmed through numerical experiments. The above important long-term relationship suggests that SSTA in K-ECS during August could serve as a valuable predictor for September precipitation over CC.