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.

 Dependence of the radiative-convective equilibrium structure of the lower atmosphere of Venus on the specification of 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 of 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.

 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.

 Inspired by two recent studies on the Pekeris mode, one of which first detected the Pekeris mode in satellite data after the eruption of the Hunga Tonga-Hunga Ha'apai (HTHH) volcano in January 2022, and the other of which obtained the theoretical equivalent depth of the Pekeris mode under the vertical temperature profile of the US Standard Atmosphere, the present manuscript calculates the theoretical equivalent depths of the Pekeris and Lamb modes under the realistic vertical temperature profile of the atmosphere after the eruption of the HTHH and longer period averages using global reanalysis data. The obtained equivalent depths depend to some extent on the location and range of the horizontal mean used to determine the vertical temperature profile, as well as the time and length of the temporal mean, but the equivalent depth of the Lamb mode is about 10.1 km, and that of the Pekeris mode is about 6.5 km. The reason why the equivalent depth of the Pekeris mode differs from the values obtained in the two recent studies mentioned above is also discussed.

 Modulation of tropical convection by the stratospheric quasi-biennial oscillation (QBO) during the Austral summer has become evident in recent studies. In this study, we show that the QBO affects the seasonal migration of the tropical convection from the equatorial Indian Ocean to the Western Pacific: large-scale convection over the Maritime Continent (MC) and western Pacific strengthens and moves eastward more effectively during easterly QBO (QBO–E) austral summers than during westerly QBO counterparts. This relationship is consistent with an enhanced Madden–Julian Oscillation (MJO) in the QBO–E. The monsoonal active convection over the Sumatra–Borneo region in December produces Kelvin wave-like low temperature anomalies in the tropical tropopause layer (TTL) over the eastern MC. These temperature anomalies strengthen when the lower stratospheric wind is easterly. We propose a hypothesis that the anomalous cooling associated with Kelvin wave-like response produces a favorable condition for a development of penetrating convection into the TTL over the eastern MC and more effective seasonal march of deep convection across the MC occurs under the QBO–E. The implication of this process for the QBO modulation of the MJO crossing the MC is also discussed.