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Abstract

Biological productivity in the Southern Ocean is modulated by iron availability. Every summer, a large phytoplankton bloom forms northwest of the Ross Sea, above the Antarctic Australian Ridge (AAR), due to a plume of iron-rich waters. Here, we investigate the origin and trajectories of these iron-rich waters by analyzing water mass observations and Lagrangian experiments. Output from the Southern Ocean State Estimate (SOSE) and in situ measurements reveal that iron-rich AAR bloom waters share properties with Modified Circumpolar Deep Water (MCDW), which forms on the Antarctic shelf-slope. The Lagrangian experiments are conducted using SOSE velocities. Bloom waters tracked with virtual Lagrangian particles highlight an along isopycnal pathway of MCDW from Antarctica's shelf-slope to the AAR bloom site, illustrating advection of these waters by the Balleny Gyre. These results are supported by temperature-salinity analyses, which show a correlation between waters advected northwards; MCDW properties; and high iron concentrations.

Abstract

Monitoring and investigation of the solar-terrestrial space environment is a huge challenge for humans in space age. To this end, China has established the Ground-based Space Environment Monitoring Network, namely Chinese Meridian Project (CMP). The project comprises three major systems: the Space Environment Monitoring System, Data and Communication System, and Scientific Application System. The Space Environment Monitoring System adopts a well-designed monitoring architecture, known as “One Chain, Three Networks, and Four Focuses,” to achieve stereoscopic and comprehensive monitoring of the entire solar-terrestrial space. The “One-Chain” component utilizes optical, radio, interplanetary scintillation, cosmic ray instruments to cover the causal chain of space weather disturbances from the solar surface to near-Earth space. For the ionosphere, middle and upper atmosphere, and magnetic field, instruments are deployed along longitudes of 120° and 100°E, and latitudes of 30° and 40°N, forming the “Three Networks.” Furthermore, more powerful monitoring facilities or large-scale instruments have been deployed in four key regions: the high-latitude polar region, mid-latitude region in northern China, low-latitude region at Hainan Island, and the Tibet region. These four regions are crucial for disturbances propagation and evolution, or possess unique geographical and topographical characteristics. The Data and Communication System and Scientific Application System are designed for data collecting, processing, storage, mining, and providing user service based on data acquired by the Space Environment Monitoring System. The data obtained by CMP will be shared with the global scientific community, facilitating enhanced collaboration on space weather and space physics research.

Abstract

The ground-based microwave radiometer (MWR) retrieves atmospheric profiles with a high temporal resolution for temperature and relative humidity up to a height of 10 km. These profiles have been widely used in the field of meteorological observation. Due to the inherent fragility of neural networks, one of the important issues in this field is to improve the reliability and stability of MWR profiles based on neural network inversion. We propose a deep learning method that adds noise to the BP neural network inversion (NBPNN) process. Comparison of the radiosonde data and NBPNN results shows that if the error of MWR brightness temperature is in the range of −2–2 K, the root-mean-square error (RMSE) of the temperature profile is 2.15 K, and the RMSE of the relative humidity profile is 19.46 % inverted by NBPNN. The results are much less than the errors of the temperature profile and relative humidity profile inverted by the traditional backpropagation neural network inverse method. From the comparison, we demonstrated that NBPNN significantly increases the inversion accuracy and robustness under the condition of errors in brightness temperature, which can reduce requirements for BT accuracy of MWR and achieve MWR long-term stability.

Abstract

Using Time History of Events and Macroscale Interactions during Substorms (THEMIS) data, we studied the stepwise development in high-latitude geomagnetic perturbations and Pi1 and Pi2 pulsations during substorm onsets and their association with stepwise auroral onset arc development by analyzing four substorm events. We found that the geomagnetic perturbations and pulsations which are magnetic signatures of the substorm on the ground show stepwise changes and excitation similar to the development of the auroral onset arc which is the visual manifestation of the substorm. We observed minor to small changes in magnetic perturbations and excitation of Pi2 pulsations before initial brightening (IB), and the subsequent excitation of Pi1 and the second Pi2 at or around the further enhancement of onset arc (FE). Then, a steep fall in the magnetic northward component, and the largest-amplitude and highest-frequency Pi1 and Pi2 pulsations appeared at or after poleward expansion (PE). The appearance of FE in all four events and its association with magnetic perturbations and pulsations suggest that FE is an important step in addition to IB and PE. The detailed analysis of the FE step using ground- and space-based data may provide information on the substorm triggering mechanism, the sequence of mechanisms behind the substorm, as well as the mechanisms responsible for the excitation of Pi1 and Pi2 pulsations.

Abstract

Energy transfer and transport in the terrestrial magnetotails are primarily driven by dipolarization fronts (DFs) embedded inside plasma jets. The DF-driven energy transfer has hitherto been believed to occur locally at the fronts. Different from the traditional knowledge, here we present the first observation of persistent energy conversion extended far behind a DF. The persistent energy conversion, which was dominated by energy loads and mainly contributed by electron currents, developed inside a turbulent, decaying flux pileup region (FPR), nearly 10 d DF (DF’s thickness) behind the DF. The energy transfer chain may be initiated by interaction between the ion flow and ambient plasmas and closed by electron dynamics, leading to electron acceleration perpendicular to magnetic field. These results highlight that electron physics in turbulent FPRs plays a crucial role in the energy transport in the planetary magnetospheres.

Abstract

Observational data sets for the high latitude middle atmosphere are key to understand the dynamics over those latitudes and the coupling between the lower and middle atmosphere. Utilizing long-term data sets from an all-sky imager at Tromsø, Norway (69.6°N, 19.2°E), the characteristics of 18 mesospheric frontal events in the Arctic winter mesosphere from 2011 to 2015 were studied. These frontal events exhibit horizontal extensions exceeding 500 km and were characterized by a sharp leading front, sometimes followed by a quasi-monochromatic wave train or a turbulent region. A subset of these frontal gravity wave events has been identified in the past as “bores.” While there have been numerous previous reports from low- and mid-latitude sites, and also from southern high latitudes, there have been a few from northern high latitudes. This study focuses on the frontal events in the northern high latitudes and provides new insights into the characteristics of these events. Their horizontal wavelengths primarily ranged from 20 to 40 km, and they exhibited phase speeds in the range 30–80 m/s. Most events were observed before local midnight. No clear link between these events and auroral activity was found. The majority of fronts were found propagating in the north-west direction, which might be due to the wind filtering effects.

Abstract

Utilizing the multi-point observations by Van Allen Probe A, GOES 13 and 15, we analyzed the competing influences of earthward convection and azimuthal drift loss on the pitch angle distributions of energetic electrons during the simultaneous increases in solar wind flow velocity and pressure. The increase in solar wind speed amplifies the dawn-dusk convection electric field and causes the earthward transport of energetic electrons, and meanwhile the enhancement of solar wind dynamic pressure causes the inward displacement of dayside magnetopause and triggers the azimuthal drift loss of energetic electrons. The earthward convection of low-energy electrons (<60 keV) is much faster than their azimuthal drift loss at most pitch angles, and the fast earthward convections make the butterfly-like electron pitch angle distributions formed early become pancake-like distributions. The 60–530 keV electrons maintain the butterfly-like pitch angle distributions during the earthward convections, whereas the high-energy electrons above 530 keV are not transported to the low-L shells because of fast drift loss in the high-L source region. The competition between the earthward convection and the azimuthal drift loss finally determines the pitch angle distributions of energetic electrons near the trapping boundary during the increases in solar wind flow speed and pressure.

Science, Volume 385, Issue 6705, July 2024.

Science, Volume 385, Issue 6705, Page 149-149, July 2024.

Science, Volume 385, Issue 6705, Page 148-148, July 2024.

Science, Volume 385, Issue 6705, Page 201-204, July 2024.

Science, Volume 385, Issue 6705, Page 174-178, July 2024.

Science, Volume 385, Issue 6705, Page 194-200, July 2024.

Science, Volume 385, Issue 6705, Page 204-209, July 2024.

Science, Volume 385, Issue 6705, Page 161-167, July 2024.

Science, Volume 385, Issue 6705, Page 216-223, July 2024.

Science, Volume 385, Issue 6705, Page 179-183, July 2024.

Science, Volume 385, Issue 6705, Page 183-187, July 2024.

Science, Volume 385, Issue 6705, Page 210-216, July 2024.

Science, Volume 385, Issue 6705, Page 226-226, July 2024.