We investigate how high seas closure will affect the availability of commonly consumed food fish in 46 fish reliant, and/or low income countries. Domestic consumption of straddling fish species (fish ...that would be affected by high seas closure) occurred in 54% of the assessed countries. The majority (70%) of countries were projected to experience net catch gains following high seas closure. However, countries with projected catch gains and that also consumed the straddling fish species domestically made up only 37% of the assessed countries. In contrast, much fewer countries (25%) were projected to incur net losses from high seas closure, and of these, straddling species were used domestically in less than half (45%) of the countries. Our findings suggest that, given the current consumption patterns of straddling species, high seas closure may only directly benefit the supply of domestically consumed food fish in a small number of fish reliant and/or low income countries. In particular, it may not have a substantial impact on improving domestic fish supply in countries with the greatest need for improved access to affordable fish, as only one third of this group used straddling fish species domestically. Also, food security in countries with projected net catch gains but where straddling fish species are not consumed domestically may still benefit indirectly via economic activities arising from the increased availability of non-domestically consumed straddling fish species following high seas closure. Consequently, this study suggests that high seas closure can potentially improve marine resource sustainability as well as contribute to human well-being in some of the poorest and most fish dependent countries worldwide. However, caution is required because high seas closure may also negatively affect fish availability in countries that are already impoverished and fish insecure.
In the Earth's magnetotail, magnetic reconnection releases stored magnetic energy and drives magnetospheric convection. The rate at which magnetic flux is transferred from the reconnection inflow to ...outflow regions is determined by the reconnection electric field Er, which is often referred to as the unnormalized reconnection rate. To better quantify the efficiency of reconnection, this electric field Er is often normalized by the characteristic Alfvén speed and the reconnecting magnetic field. This parameter is generally called the normalized or dimensionless reconnection rate R. In this paper, we employ a two‐dimensional fully kinetic simulation to model a magnetotail reconnection event with weak geomagnetic activity (<200 nT of the AE index) observed by the Magnetospheric Multiscale (MMS) mission on 11 July 2017. We obtain R and Er from direct measurements in the diffusion region and indirect measurements of the rate at the separatrix using a recently proposed remote sensing technique. The measured normalized rate for this MMS event is R ∼0.15–0.2, consistent with theoretical and simulation models of fast collisionless reconnection. This corresponds to an unnormalized rate of Er ∼2–3 mV/m. Based on quantitative consistencies between the simulation and the MMS observations, we conclude that our estimates of the reconnection rates are reasonably accurate. Given that past studies have found Er of the order ∼10 mV/m during strong geomagnetic substorms, these results indicate that the local Er in magnetotail reconnection may be an important parameter controlling the amplitude of geomagnetic disturbances.
Key Points
Reliable reconnection rates are obtained based on virtual observations in a fully kinetic simulation of an MMS tail reconnection event
The normalized rates obtained from the simulation and MMS data are 0.15–0.2, indicating the occurrence of fast reconnection
The observed unnormalized rate is 2–3 mV/m, while higher rates were observed in other events with stronger geomagnetic activities
Climate change-reflected in significant environmental changes such as warming, sea level rise, shifts in salinity, oxygen and other ocean conditions-is expected to impact marine organisms and ...associated fisheries. This study provides an assessment of the potential impacts on, and the vulnerability of, marine biodiversity and fisheries catches in the Arabian Gulf under climate change. To this end, using three separate niche modelling approaches under a 'business-as-usual' climate change scenario, we projected the future habitat suitability of the Arabian Gulf (also known as the Persian Gulf) for 55 expert-identified priority species, including charismatic and non-fish species. Second, we conducted a vulnerability assessment of national economies to climate change impacts on fisheries. The modelling outputs suggested a high rate of local extinction (up to 35% of initial species richness) by 2090 relative to 2010. Spatially, projected local extinctions are highest in the southwestern part of the Gulf, off the coast of Saudi Arabia, Qatar and the United Arab Emirates (UAE). While the projected patterns provided useful indicators of potential climate change impacts on the region's diversity, the magnitude of changes in habitat suitability are more uncertain. Fisheries-specific results suggested reduced future catch potential for several countries on the western side of the Gulf, with projections differing only slightly among models. Qatar and the UAE were particularly affected, with more than a 26% drop in future fish catch potential. Integrating changes in catch potential with socio-economic indicators suggested the fisheries of Bahrain and Iran may be most vulnerable to climate change. We discuss limitations of the indicators and the methods used, as well as the implications of our overall findings for conservation and fisheries management policies in the region.
Abstract
Coalescence of multiple magnetic islands is recognized as an effective process to energize particles during magnetic reconnection, while its energy conversion process still remains unclear. ...Here, a two-dimensional fully kinetic simulation of multiple island coalescence with a small reconnection guide field is studied. In the analysis of energy conversion within a magnetic island, the dot product of
V
e
·
j
×
B
=
w
1
is a useful quantity to compare with
j
·
E
=
w
2
, since the average work done by the Lorentz force on the circulating particles is negligible in the island and
w
2
−
w
1
=
j
·
E
+
V
e
×
B
=
j
·
E
′
=
w
3
. A bipolar pattern of
w
1
is found at a secondary island when the electrons are in circular motion inside the island. Significant energy dynamo (
w
3
< 0) resulting from
j
∥
E
∥
is found at the secondary island, which has not been reported before, where the parallel electric field
E
∥
is highly correlated with
w
3
. Moreover, significant energy dissipation (
w
3
> 0) due to
j
⊥
·
E
⊥
′
is seen in the merging region between two coalescing islands. Both types of energy conversions are accompanied by enhancements in
j
∥
and the parallel electron temperature
T
e
∥
. Three ion-scale magnetic islands (FR1, FR2, and FR3) observed by the Magnetospheric Multiscale spacecraft are compared favorably with the simulated signatures of energy dynamo and dissipation of an evolving secondary island. In particular, FR1 displayed a similar energy dynamo signature as that simulated in an early stage of the secondary island. FR2 and FR3 showed a dominant
j
⊥
·
E
⊥
′
energy conversion similar to that obtained in a later stage of the secondary island.
We examine traversals on 20 November 2001 of the equatorial magnetopause boundary layer simultaneously at ∼1500 magnetic local time (MLT) by the Geotail spacecraft and at ∼1900 MLT by the Cluster ...spacecraft, which detected rolled‐up MHD‐scale vortices generated by the Kelvin‐Helmholtz instability (KHI) under prolonged northward interplanetary magnetic field conditions. Our purpose is to address the excitation process of the KHI, MHD‐scale and ion‐scale structures of the vortices, and the formation mechanism of the low‐latitude boundary layer (LLBL). The observed KH wavelength (>4 × 104 km) is considerably longer than predicted by the linear theory from the thickness (∼1000 km) of the dayside velocity shear layer. Our analyses suggest that the KHI excitation is facilitated by combined effects of the formation of the LLBL presumably through high‐latitude magnetopause reconnection and compressional magnetosheath fluctuations on the dayside, and that breakup and/or coalescence of the vortices are beginning around 1900 MLT. Current layers of thickness a few times ion inertia length ∼100 km and of magnetic shear ∼60° existed at the trailing edges of the vortices. Identified in one such current sheet were signatures of local reconnection: Alfvénic outflow jet within a bifurcated current sheet, nonzero magnetic field component normal to the sheet, and field‐aligned beam of accelerated electrons. Because of its incipient nature, however, this reconnection process is unlikely to lead to the observed dusk‐flank LLBL. It is thus inferred that the flank LLBL resulted from other mechanisms, namely, diffusion and/or remote reconnection unidentified by Cluster.
With high time‐resolution field and plasma measurements by the Magnetospheric Multiscale spacecraft, interior fine structures of two ion‐scale magnetic flux ropes (~5 and ~11 ion inertial length ...radius) separated by ~14 s are resolved. These two ion‐scale flux ropes (FR1 and FR2) show non‐frozen‐in ion behavior and consist of a strong axial magnetic field at the reversal of the negative‐then‐positive bipolar field component. The negative bipolar field component of the FR2 is found to be depressed, where magnetic pressure and total pressure decrease, but ion and electron thermal pressures increase, a feature akin to a crater‐like flux rope. The pressure enhancement is due to the magnetosheath plasma feeding into the flux rope along the field lines. Magnetic field draping and energetic electrons are also observed in the trailing part of the FR2. The ratio of perpendicular and parallel currents indicates that the FR1 appears force‐free but the FR2 seems not. Moreover, the FR2 is time‐dependent as a result of a low correlation coefficient (CC = 0.75) for the derivation of the deHoffmann‐Teller frame using the direct measured electric fields, while the FR1 is in quasi‐steady conditions (CC = 0.94). It is concluded that the crater formation within the FR2 can be interpreted by the analytical flux rope simulation as the evolution of typical flux rope to crater‐like one due to the thermal pressure enhancement, which could be induced by the depression of transverse magnetic fields of the flux rope.
Key Points
Interior fine structures of two ion‐scale flux ropes are resolved for which some of their flux rope properties are contrasted
Crater is formed within one flux rope where magnetic pressure decreases while thermal pressure increases
Crater formation can be interpreted by flux rope simulation as evolution of typical flux rope to crater‐like one due to pressure increase
•We develop the run sum charts for monitoring the coefficient of variation (CV).•The CV is successfully applied in various scientific and societal disciplines.•The ARL, SDRL and EARL formulae are ...derived through a Markov chain approach.•Optimal designs are based on the deterministic and unknown shift-size conditions.•New optimal charts’ parameters under the zero- and steady-state modes are given.
The coefficient of variation (CV) is a unit-free and effective normalized measure of dispersion. Monitoring the CV is a crucial approach in Statistical Process Control when the quality characteristic has a distinct mean value and its variance is a function of the mean. This setting is common in many scientific areas, such as in the fields of engineering, medicine and various societal applications. Therefore, this paper develops a simple yet efficient procedure to monitor the CV using run-sum control charts. The run-length properties of the run-sum CV (RS-γ) charts are characterized by the Markov chain approach. This paper proposes two optimization algorithms for the RS-γ charts, i.e. by minimizing (i) the average run length (ARL) for a deterministic shift size and (ii) the expected ARL over a process shift domain. Performance comparisons under both the zero- and steady-state modes are made with the Shewhart-γ, Run-rules-γ and EWMA-γ charts. The results show that the proposed RS-γ charts outperform their existing counterparts for all or certain ranges of shifts in the CV. The application of the optimal RS-γ charts is illustrated with real data collected from a casting process.
In the solar wind Alfvénic fluctuations are coupled fluctuations in the transverse components of plasma velocity, , and magnetic field, , in which remains nearly constant. Consequently, the ...fluctuations in the component of and along the direction of the underlying magnetic field, , are always one-sided relative to base values rather than mean values. This paper proposes a new method for estimating and verifies it using simulation data. The new approach is to find a consistent minimum variance direction of magnetic field for two different data subsets divided by a threshold angle from the original data set. Simulation results show that (1) the direction of predicted by the new method is generally more accurate than the average magnetic field, , and that (2) does not correspond to when the averages of the transverse field fluctuations are nonzero. Two events of one-sided Alfvénic fluctuations in the solar wind observed at 0.36 and 1 au, where a small but significant mean appears in the transverse field fluctuation, are demonstrated for the new method. Results show that the new estimate is more radial than and also different from that predicted by Parker's model of the heliospheric magnetic field (HMF). This new technique will be useful for comparing solar wind observations with the global HMF model and for determining the fluctuation k-vector, which is presumably directed along .
Governance of South China Sea (SCS) fisheries remains weak despite acknowledgement of their widespread overexploitation for the past few decades. This review incorporates unreported fish catches to ...provide an improved baseline of the current status and societal contribution of SCS marine fisheries, so that the socio-economic and ecological consequences of continued fisheries unsustainability may be understood. Potential fisheries contribution to food and livelihoods include 11-17 million t in fisheries catch and USD 12-22 × 10⁹ in fisheries landed value annually in the 2000s, and close to 3 million jobs. However, overfishing has resulted in biodiversity and habitat loss, and altered ecosystem trophic structures to a 'fished down' state. The present situation reiterates the urgency for fisheries policies that simultaneously address multiple political, social, economic, and biological dimensions at regional, national, and local scales. Importantly, improved cooperation between SCS nations, particularly in overcoming territorial disputes, is essential for effective regional fisheries governance.
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