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International audience; Inconsistencies in the Eocene climates of East Asia have been revealed in both geological studies and simulations. Several earlier reconstructions showed an arid zonal band in mid-latitude China, but others showed a humid climate in the same region. Moreover, previous Eocene modeling studies have demonstrated that climate models can simulate both scenarios in China. Therefore, it is essential to investigate the cause of this model spread. We conducted a series of experiments using Norwegian Earth System Model 1-F and examined the impact of mountains in Southern China on the simulated Eocene climate. These mountains, including the Gangdese and Southeast Mountains, are located along the main path of water vapor transport to East Asia. Our results reveal that the Southeast Mountains play the dominant role in controlling the simulated precipitation in Eastern China during the Eocene. When the heights of the Southeast Mountains exceed ∼2,000 m, an arid zonal band appears in mid-latitude China, whereas humid climates appear in Eastern China when the elevation of the Southeast Mountains is relatively low.

Unipolar pulses of kinetic Alfven waves (KAW) are first observed in the near-Earth plasma sheet (NEPS) associated with dipolarizations during substorm expansion phases. Two similar events are studied with Time History of Events and Macroscale Interactions during Substorms (THEMIS) observations during substorms on 3 February 2008 and 7 February 2008. The unipolar pulses were located at a trough-like Alfven speed profile in the northern plasma sheet at a distance of 10–11 R E from Earth. The dominant wave components consist of a southward δ E z toward the neutral plane and a +δ B y toward the dusk. The |δ E z |/|δ B y | ratio was in the range of a few times the local Alfven speed, a strong indication of KAW nature. The wave Poynting flux was earthward and nearly parallel to the background magnetic field. The pulse was associated with an earthward field-aligned current carried by electrons. These observational facts strongly indicate a KAW eigenmode that is confined by the plasma sheet but propagates earthward along the field line. The KAW eigenmode was accompanied by short timescale (1 min) dipolarizations likely generated by transient magnetotail reconnection. The observed polarity of the KAW field/current is consistent with that of the Hall field/current in magnetic reconnection, supporting the scenario that the Hall fields/current propagate out from reconnection site as KAW eigenmodes. Aurora images on the footprint of THEMIS spacecraft suggest that KAW eigenmode may power aurora brightening during substorm expansion phase.

A substorm dispersionless injection event observed during the storm recovery phase on 11 March 1998 at geosynchronous orbit is carefully studied. The event shows the notable characteristics that for energetic ions the flux enhancement ratio before and after injection increases and remains elevated with increasing energy, while for energetic electrons it tends to decrease with increasing energy. In order to explain the unique injection feature, the authors propose a possible mechanism that velocity space diffusion in common to electric acceleration adjusts the particle injection state. Spectral characteristics of four different phases (pregrowth phase, the growth phase, the substorm expansion phase, and the recovery phase) have been investigated. The differential fluxes of electrons from 50 keV to 1.5 Mev and ions from 50 keV to 1.2 MeV measured by Synchronous Orbit Plasma Analyzer (SOPA) instrument onboard LANL satellite 1991-080 are found to be best fitted with the three-parameter kappa distribution function (f similar to A(0) . E[1 + E / (kappa E-0)](-kappa-1)) by Levenberg-Marquardt and Universal Global Optimization methods. The evolutions of the three parameters in the above kappa distribution in different substorm phases have been depicted for both electrons and ions. In each phase, E-0 and kappa show an approximately linear relationship kappa(E-0) = kappa(0) + eta E-0. This linear relationship can be obtained by solving the velocity space diffusion equation with an initial superthermal kappa distribution. Ion and electron are found to have opposite trend of parameters kappa(0) and eta in each phase, which indicates that the different species of particles exert different velocity space diffusion processes so that their flux enhancement ratios before and after injection are rather different. This implies that not only electric field acceleration, but also velocity space diffusion plays a very important role in the particle injection.

[1] The Neutral Atom Detector Unit (NUADU) aboard the TC-2 spacecraft recorded energetic neutral atom (ENA) image data for >3 h during part of the main and recovery phases of a major magnetic storm on 15 May 2005. A custom designed, constrained linear inversion method was applied to retrieve ring current ion distributions in the ENA records out to L = 6.6. Comparisons were then made between the ion fluxes retrieved from these ENA data (energy ranges 50–81 keV and 81–158 keV) and complementary, contemporaneous particle fluxes measured in situ by Synchronous Orbit Particle Analyzer (SOPA) instruments aboard a series of geosynchronous satellites that were launched to encircle the equatorial plane at L ∼ 6.6 by the Los Alamos National Laboratory (LANL). The ENA data revealed the development of two emission peaks during the main phase of the storm which corresponded to the arrival from the magnetotail of a pair of particle injections. These injections reached, in each case, maximum value before the corresponding AL index amplitude peak was attained. The main phase of the storm concluded (Dst ≈ −256 nT) in the aftermath of this event pair, and the ring current ion fluxes thereafter gradually decayed over several hours (the storm recovery phase). This is the first time that the linear inversion method developed for NUADU data has been globally validated using multipoint in situ measurements made at different magnetic local times. It was found that the higher the derived flux values were on the duskside/nightside, the closer they were to the in situ measurements. The retrieved fluxes obtained on the duskside/nightside tended, however, to be still somewhat underestimated since the ENA measurements concerned were made around the outer edge of the ring current at an altitude where the magnetic field in the inner magnetosphere deviates from that dipole configuration assumed in the inversion procedure to pertain there. The two methods utilized to study ions during a large magnetic storm are complementary in that the retrieved ion fluxes provide high time resolution information concerning the changing, large-scale structure of ring current events, whereas in situ flux sampling presents “measurement truth” at particular locations within individual ring currents.