Junke Zhang

GIC due to storm sudden commencement in low‐latitude high‐voltage power network in China: Observation and simulation

The impact of geomagnetically induced currents (GICs) on the power networks at middle and low latitudes has attracted attention in recent years with the increase of large-scale power networks. In this study, we report the GIC monitored at two low-latitude 500xa0kV substations of China during the large storm of 17 March 2015. The GIC due to the storm sudden commencement (SSC) was much higher than that during the storm main phase. This phenomenon is more likely to happen at low-latitude locations, highlighting the importance of SSC in inducing GIC in low-latitude power networks. Furthermore, we ran a global MHD model to simulate the GIC during this SSC event by using the solar wind observation as input. The model results reproduced the main features of the GIC. The study also indicated that the eastward component of the geoelectric field is dominant for low-latitude locations during the SSC events. Further, topology and electrical parameters of the power grids make significant differences in the GIC levels.

Regional pollution and its formation mechanism over North China Plain: A case study with ceilometer observations and model simulations

To investigate regional haze formation, ceilometer observations at the Beijing (BJ), Shijiazhuang (SJZ), Tianjin (TJ), and Qinhuangdao (QHD) stations were conducted from 12 October to 10 November 2014, to obtain the boundary layer height (BLH) and the attenuated backscattering coefficients (ABC). Particles at the four stations were highly correlated, whereas precursors of particles exhibited weaker correlations. By analyzing the typical haze episode between 21 and 26 October 2014, we found that warm advection at a height of 850u2009hPa from the Loess Plateau caused a gradual decline in the regional BLH. Moreover, water vapor transported from the southern NCP caused the column water vapor amount to increase from 0.015u2009kgu2009m−2 to 0.042u2009kgu2009m−2 in the boundary layer in BJ. As southerly transport prevailed during the transition period, ABC profiles in the BJ, TJ, and QHD stations showed a bilayer pattern, and the second layer was between 500 and 1000u2009m. As a result, the ABC integrations of BJ and TJ increased by 74.2 and 139.7%, respectively. During the polluted period, due to the weakened transport effect, the ABC integrations of the four stations decreased by 7.9, 18.2, 16.2, and 28.2%, respectively. Contributions of the secondary inorganic species (sulfate, nitrate, and ammonium) at BJ increased from 37.3% to 56.9%, and the mean particle size increased from 107.8u2009nm to 140.8u2009nm. Emissions in southern NCP should be mitigated during the transition period, whereas the inorganic precursors are the most important air pollutants during the polluted period.

The chain response of the magnetospheric and ground magnetic field to interplanetary shocks

In response to interplanetary (IP) shocks, magnetic field may decrease/increase (negative/positive response) in nightside magnetosphere, while at high latitudes on the ground it has two-phase bipolar variations: preliminary impulse and main impulse (MI). Using global MHD simulations, we investigate the linkage between the MI phase variation on the ground and the magnetospheric negative response to an IP shock. It is revealed that although the two phenomena occur at largely separated locations, they are physically related and form a response chain. The velocity disturbances near the flanks of the magnetopause cause the magnetic field to decrease, resulting in a dynamo which thus powers the transient field-aligned currents (FACs). These FACs further generate a pair of ionospheric current vortex, leading to MI variations on the ground. Therefore, we report here the intrinsic physically related chain response of the magnetospheric and ground magnetic field to IP shocks, and thus link the magnetospheric sudden impulse (SI) and ground SI together.

Modeling geomagnetically induced electric field and currents by combining a global MHD model with a local one-dimensional method

Geomagnetically induced currents (GIC) flowing in long conductor systems on the ground are a well-known space weather hazard. We develop a new approach to simulating GICs by combining a global MHD model with a local one-dimensional method. As an example, we apply this approach to model the GIC at the Pirttikoski 400 kV transformer of the Finnish high-voltage power system during the space weather event of 22-23 September 1999. The modeled results can capture the main observational features, and the model performances is better than two GIC persistence models, which demonstrates this promising new approach in GIC forecasting.

Comparison of equivalent current systems for the substorm event of 8 March 2008 derived from the global PPMLR-MHD model and the KRM algorithm

Geomagnetic perturbation is an important aspect to determine the capability of a 3-D MHD model in predicting space weather. Taking the substorm event of 8 March 2008 as an example, we compare the equivalent current systems (ECS) in the ionosphere derived from the global PPMLR-MHD simulation model and the ground-based magnetic field observations using the KRM inversion algorithm. The evolution of ECS is utilized to give a global view of the temporal and spatial development of the magnetic fields on the ground. The PPMLR-MHD model has generally reproduced the main characters of the large-scale magnetic field variation on the ground. The magnetic latitude and local time distribution of the ECS is in reasonably agreement with the inversion results during the disturbed period. We hopefully consider the ECS to be a promising numerical forecast product of the global geomagnetic variation from an global 3-D MHD model in the future.

Characteristics, source apportionment and reactivity of ambient volatile organic compounds at Dinghu Mountain in Guangdong Province, China

Volatile organic compounds (VOCs) play a very important role in the formation of ozone and secondary organic aerosols. The concentrations, compositions, and variability of VOCs were measured from 2005 to 2008 at Dinghu Mountain Forest Ecosystem Research Station, a remote station in Southeast China. Weekly samples were collected in the Dinghu Mountain area and were analysed via gas chromatography-mass spectrometry. The results revealed that the total VOC concentrations decreased continuously and that the dominant VOC components were alkanes (43%) and aromatics (33%), followed by halo-hydrocarbons (12%) and alkenes (12%). The general trend of seasonal variation indicated higher concentrations in spring and lower concentrations in summer. The positive matrix factorization model was used to identify the sources of the VOCs. Seven sources were resolved by the PMF model: (1) vehicular emissions, which contributed 25% of the total VOC concentration; (2) industrial sources and regional transportation, contributing 17%; (3) paint solvent use, contributing 17%; (4) fuel evaporation, contributing 13%; (5) stationary combustion sources, contributing 12%; (6) biogenic emissions, contributing 10%; and aged VOCs, contributing only 6%. The HYSPLIT model was used to analyse the effect of pollutant transport, and the results indicated that the transport of pollutants from cities cannot be ignored. Finally, the OH radical loss rates and ozone formation potentials (OFPs) were calculated, and the results indicated isoprene to have the highest OH radical loss rate and toluene to be the largest contributor to the OFP at the Dinghu Mountain site.

Source appointment of fine particle number and volume concentration during severe haze pollution in Beijing in January 2013

Extreme haze episodes repeatedly shrouded Beijing during the winter of 2012–2013, causing major environmental and health problems. To better understand these extreme events, particle number size distribution (PNSD) and particle chemical composition (PCC) data collected in an intensive winter campaign in an urban site of Beijing were used to investigate the sources of ambient fine particles. Positive matrix factorization (PMF) analysis resolved a total of eight factors: two traffic factors, combustion factors, secondary aerosol, two accumulation mode aerosol factors, road dust, and long-range transported (LRT) dust. Traffic emissions (54xa0%) and combustion aerosol (27xa0%) were found to be the most important sources for particle number concentration, whereas combustion aerosol (33xa0%) and accumulation mode aerosol (37xa0%) dominated particle volume concentrations. Chemical compositions and sources of fine particles changed dynamically in the haze episodes. An enhanced role of secondary inorganic species was observed in the formation of haze pollution. Regional transport played an important role for high particles, contribution of which was on average up to 24–49xa0% during the haze episodes. Secondary aerosols from urban background presented the largest contributions (45xa0%) for the rapid increase of fine particles in the severest haze episode. In addition, the invasion of LRT dust aerosols further elevated the fine particles during the extreme haze episode. Our results showed a clear impact of regional transport on the local air pollution, suggesting the importance of regional-scale emission control measures in the local air quality management of Beijing.

V753 MON: A UNIQUE CLOSE BINARY JUST AFTER THE EVOLUTIONARY STAGE WITH THE SHORTEST PERIOD DURING MASS TRANSFER

We discovered that the O-C curve of V753 Mon shows an upward parabolic change while undergoing a cyclic variation with a period of 13.5 yr. The upward parabolic change reveals a long-term period increase at a rate of (P) over dot = +7.8 x 10(-8) days yr(-1). Photometric solutions determined using the Wilson-Devinney method confirm that V753 Mon is a semi-detached binary system where the slightly less massive, hotter component star is transferring mass to the more massive one. This is in agreement with the long-term increase of the orbital period. The increase of the orbital period, the mass ratio very close to unity, and the semi-detached configuration with a less massive lobe-filling component all suggest that V753 Mon is on a key evolutionary stage just after the evolutionary stage with the shortest period during mass transfer. The results in this paper will shed light on the formation of massive contact binaries and the evolution of binary stars. The cyclic oscillation in the O-C diagram indicates that V753 Mon may be a triple system containing an extremely cool stellar companion that may play an important role for the formation and evolution in the binary system.

Risk assessment of the extreme interplanetary shock of 23 July 2012 on low‐latitude power networks

Geomagnetic sudden commencements (SCs), characterized by a rapid enhancement in the rate of change of the geomagnetic field perturbation (dB/dt), are considered to be an important source of large geomagnetically induced currents (GICs) in middle- and low-latitude power grids. In this study, the extreme interplanetary shock of 23 July 2012 is simulated under the assumption that it had hit the Earth with the result indicating the shock-caused SC would be 123nT. Based on statistics, the occurrence frequency of SCs with amplitudes larger than the simulated one is estimated to be approximately 0.2% during the past 147 years on the Earth. During this extreme event, the simulation indicates that dB/dt, which is usually used as a proxy for GICs, at a dayside low-latitude substation would exceed 100nT/min; this is very large for low-latitude regions. We then assess the GIC threat level based on the simulated geomagnetic perturbations by using the method proposed by Marshall et al. (2011). The results indicate that the risk remains at low level for the low-latitude power network on a global perspective. However, the GIC risk may reach moderate or even high levels for some equatorial power networks due to the influence of the equatorial electrojet. Results of this study feature substantial implications for risk management, planning, and design of low-latitude electric power networks.

1SWASP J074658.62+224448.5: A LOW MASS-RATIO CONTACT BINARY AT THE PERIOD CUTOFF

The first sets of high-quality light curves of the extremely short period eclipsing binary 1SWASP J074658.62+224448.5 (hereafter J074658) were obtained in 2012 and 2014. The photometric solutions were derived using the 2013 version of the Wilson-Devinney code. Two different modes of overcontact binaries were used to analyze the light curves, and the adopted solutions show that J074658 is a shallow contact system (the degree of contact is f = 13.1 +/- 2.1%) with a mass ratio of q= 0.386 +/- 0.017. The two components have very close temperatures, which may indicate that J074658 is in thermal contact. The variation of the orbital period was studied using all the available times of minimum light. According to the O - C diagram, the orbital period of J074658 shows an increase at a rate of P = 5.39 10(-7) days yr(-1) in about an eight-year span. The reasons for the period increase compared with other well-studied contact binaries with extremely short periods are discussed. The period increase may be caused by mass transfer from the less massive component to the more massive one, or it could be only part of a long period cyclic variation that may reveal the presence of a third body. In this paper, the latter is suggested.