T. Y. Wang

Sulfur dioxide vertical column DOAS retrievals from the Ozone Monitoring Instrument: Global observations and comparison to ground-based and satellite data

We present a new data set of sulfur dioxide (SO2) vertical columns from observations of the Ozone Monitoring Instrument (OMI)/AURA instrument between 2004 and 2013. The retrieval algorithm used is an advanced Differential Optical Absorption Spectroscopy (DOAS) scheme combined with radiative transfer calculation. It is developed in preparation for the operational processing of SO2 data product for the upcoming TROPOspheric Monitoring Instrument/Sentinel 5 Precursor mission. We evaluate the SO2 column results with those inferred from other satellite retrievals such as Infrared Atmospheric Sounding Interferometer and OMI (Linear Fit and Principal Component Analysis algorithms). A general good agreement between the different data sets is found for both volcanic and anthropogenic SO2 emission scenarios. We show that our algorithm produces SO2 columns with low noise and is able to provide accurate estimates of SO2. This conclusion is supported by important validation results over the heavily polluted site of Xianghe (China). Nearly 4 years of OMI and ground-based multiaxis DOAS SO2 columns are compared, and an excellent match is found. We also highlight the improved performance of the algorithm in capturing weak SO2 sources by detecting shipping SO2 emissions in long-term averaged data, an unreported measurement from space.

Growth, abscisic acid content, and carbon isotope composition in wheat cultivars grown under different soil moisture

Changes in dry matter accumulation and allocation, abscisic acid content and carbon isotope composition of three wheat cultivars from dry, middle and wet climate regions were recorded at full maturity after exposure to different watering regimes (100, 50 and 25 % field capacity). Compared with the wet climate cultivar, the dry climate cultivar showed lower stem height, total leaf area, total dry biomass and total grain dry mass, and higher root/shoot ratio, abscisic acid content and carbon isotope composition under all watering regimes. Both water-limited treatments significantly reduced leaf growth and increased dry matter allocation into the roots leading to a significant raise of root/shoot ratio in all cultivars tested. In addition, drought affected morphological and physiological properties more in the dry climate cultivar than in the wet climate cultivar.

Storm time evolution of ELF/VLF waves observed by DEMETER satellite

In this paper, using the data of Sun-synchronous satellite (Detection of Electro-Magnetic Waves Transmitted from Earthquake Regions) DEMETER, we investigated the storm time variations of ELF/VLF waves during the intense coronal mass ejections (CME)-driven storms from 2005 to 2009. The results show that there is a good correlation between the enhancement of ELF/VLF waves and the CME events. Immidately following the enhanced wave activity driven by CMEs at the initial phase, the wave intensity decreases temporarily at the beginning of storm main phase. The strongest waves predominantly occur from the late main phase to early recovery phase. The ELF waves below 3 kHz are significantly intensified during the whole storm time, while the high-frequency waves above 3 kHz seem strengthened predominantly during the late main and early recovery phase. The ELF waves below 3 kHz can exist in a wide L shell range, with the intensity peaking at L ~ 3 and 4. High-frequency waves at f > 9 kHz exist mostly outside the plasmapause. The stronger ELF/VLF waves on the dayside can last longer time than those on the nightside.

Polytropic index of central plasma sheet ions based on MHD Bernoulli integral

This paper uses the data of Cluster from 2001 to 2009 to study the polytropic processes of central plasma sheet (CPS) ions. We first adopt the approach of MHD Bernoulli integral (MBI) to identify homogeneous streamflow tubes (quasi-invariant MBI regions) and then calculate the polytropic index of ions for those streamflow tubes whose outward electromagnetic energy ratios δ  < 0.05. The central plasma sheet is actually a complicated system, which comprises many streamflow tubes with different polytropic relations and the transition layers in between. The polytropic indexes of the CPS ions range from 0.1 to 1.8 and have a quasi-Gaussian distribution. The median polytropic index is 0.93 for AE < 200 nT and 0.91 for AE ≥ 200 nT. Thus, there is no obvious difference between the polytropic indexes of the quiet time and the substorm time CPS ions, which suggests that the thinning and thickening processes of plasma sheet during substorm times do not change obviously the polytropic relation of the CPS ions. The statistical analysis using different δ (δ < 0.05, 0.025, and 0.01) shows that the outward emission of electromagnetic energy is an effective cooling mechanism and can make the polytropic index to decrease and shift toward isobaric. It is inferred that the CPS ions as a whole much likely behave in a way between isobaric and isothermal.

Different responses of two contrasting wheat genotypes to abscisic acid application

Purpose of this study was to investigate different responses of two wheat genotypes (Triticum aestivum L.) from the wet and dry climate regions to exogenous abscisic acid (ABA) application under well-watered and water-stressed conditions. Exogenous ABA was applied to the leaves by spraying and changes in dry matter accumulation and allocation, endogenous ABA content and carbon isotope ratio (δ13C) were monitored. The ABA application significantly decreased stem height, total biomass, total leaf area, total grain mass and leaf area/mass ratio, and significantly increased root/aboveground biomass ratio, endogenous ABA content and δ13C under well-watered and water-stressed conditions. Compared with the wet climate genotype, the dry climate genotype was more responsive to exogenous ABA application, resulting in lower stem height, total biomass, total leaf area, total grain mass and leaf area/mass ratio, and higher root/aboveground biomass ratio, endogenous ABA content and δ13C under all experimental treatments.

Suprathermal electron acceleration in the near-Earth flow rebounce region

Flux pileup regions (FPRs) are traditionally referred to the strong-Bz bundles behind dipolarization fronts (DFs) in the Earths magnetotail and can appear both inside earthward and tailward bursty bulk flows. It has been widely reported that suprathermal electrons (40–200 keV) can be efficiently accelerated inside earthward FPRs, leaving the electron acceleration inside tailward FPRs as an open question. In this study, we focus on the electron acceleration inside a tailward FPR that is formed due to the flow rebounce in the near-Earth region (XGSM ≈ −12 RE) and compare it quantitatively with the acceleration inside an earthward FPR. By examining the Cluster data in 2008, we sequentially observe an earthward FPR and a tailward FPR in the near-Earth region, with the earthward one belonging to decaying type and the tailward one belonging to growing type. Inside the earthward FPR, Fermi acceleration and betatron cooling of suprathermal electrons are found, while inside the tailward FPR, Fermi and betatron acceleration occur. Whistler-mode waves are observed inside the tailward FPR; their generation process may still be at the early stage. We notice that the suprathermal electron fluxes inside the tailward FPR are about twice as large as those inside the earthward FPR, suggesting that the acceleration of suprathermal electrons is more efficient in the flow rebounce region. These acceleration processes have been successfully reproduced using an analytical model; they emphasize the role of flow rebounce in accelerating suprathermal electrons and further reveal how the MHD-scale flow modulates the kinetic-scale electron dynamics in the near-Earth magnetotail.

Compressible turbulence with slow‐mode waves observed in the bursty bulk flow of plasma sheet

In this paper, we report the evidence of compressible turbulence with slow-mode waves in a bursty bulk flow of plasma sheet. This compressible turbulence is characterized by a multiscale (1–60 s) anticorrelation between plasma density and magnetic field strength. Besides, the magnetic compressibility spectrum stays nearly constant at all the measured frequencies. Furthermore, the turbulence energy distributions are anisotropic with k⊥ > k//, and the dispersion relation is consistent with slow-mode prediction. The fluctuations of density and magnetic field have similar double slope spectrum and kurtosis. These results suggest that the slow waves are involved in the intermittent turbulence cascade from MHD to ion kinetic scales, which may have significant implications for the energy transfer in the plasma sheet.

Turbulence in the Earth's cusp region: The k‐filtering analysis

On 13 April 2002, four Cluster spacecraft with separations up to 127 km measured similar turbulence in the exterior cusp during northward interplanetary magnetic field (IMF) B-z. Both the power spectra of magnetic and electric field fluctuations resemble the classical Kolmogorov power law, with the scaling f (-1.7) under the proton gyrofrequency f(cp) (similar to 0.3 Hz), breaks near f(cp), and then steepens with the scalings f (-2.8) and f(-2.0) up to 10 Hz, respectively. The observed ratio of the electric to magnetic field is in agreement with the theoretical values of vertical bar delta E/delta B vertical bar for the quasi-perpendicular kinetic Alfven waves (KAWs), which reflects the features of Alfven turbulence. The wave vector and dispersion relation of the turbulence are obtained using k-filtering technique. The results show that the waves propagate quasi-perpendicularly to the background magnetic field. The similarity between the experimental and the theoretical dispersion relations indicates that the measured waves are kinetic Alfvn wave. The waves have right-handed elliptical polarization in the plane perpendicular to k. Themain axis of polarization ellipse is perpendicular to the average magnetic field. These features furthermore indicate that the turbulence properties agree well with those of KAW mode. The observed KAW is much possibly produced through resonance mode conversion. We calculate the density gradient vector using multipoint density data and found that the waves propagate basically toward high-density region. The density gradient in the exterior cusp provides a favorable condition for the resonance converted KAW.

Case study of small scale polytropic index in the central plasma sheet

This paper studies the effective polytropic index in the central plasma sheet (CPS) by using the method of Kartalev et al. (2006), which adopts the denoising technique of Haar wavelet to identify the homogeneous MHD Bernoulli integral (MBI) and has been frequently used to study the polytropic relation in the solar wind. We chose the quiet CPS crossing by Cluster C1 during the interval 08:51:00–09:19:00 UT on 03 August 2001. In the central plasma sheet, thermal pressure energy per unit mass is the most important part in MBI, and kinetic energy of fluid motion and electromagnetic energy per unit mass are less important. In the MBI, there are many peaks, which correspond to isothermal or near isothermal processes. The interval lengths of homogenous MBI regions are generally less than 1 min. The polytropic indexes are calculated by linearly fitting the data of lnp and lnn within a 16 s window, which is shifted forward by 8 s step length. Those polytropic indexes with |R|⩾0.8 (R is the correlation coefficient between lnp and lnn) and p-value⩽0.1 in the homogeneous regions are almost all in the range of [0, 1]. The mean and median effective polytropic indexes with high R and low p-value in homogeneous regions are 0.34 and 0.32 respectively, which are much different from the polytropic index obtained by traditional method ( αtrad=−0.15). This result indicates that the CPS is not uniform even during quiet time and the blanket applications of polytropic law to plasma sheet may return misleading value of polytropic index. The polytropic indexes in homogeneous regions with a high correlation coefficient basically have good regression significance and are thus credible. These results are very important to understand the energy transport in magnetotail in the MHD frame.

Quadrupolar pattern of the asymmetric guide-field reconnection

With high-resolution data of the recently launched Magnetospheric Multiscale (MMS) mission, we report a magnetic reconnection event at the dayside magnetopause. This reconnection event, having a density asymmetry Nhigh/Nlow≈2 on the two sides of the reconnecting current sheet and a guide field Bg≈0.4B0 in the ‘out-of-plane’ direction, exhibit all the two-fluid features: Alfvenic plasma jets in the outflow region, bipolar Hall electric fields toward the current sheet center, quadrupolar Hall magnetic fields in the ‘out-of-plane’ direction, and the corresponding Hall currents. Obviously, the density asymmetry Nhigh/Nlow≈2 and the guide field Bg≈0.4B0 are not sufficient to dismiss the quadrupolar pattern of Hall reconnection. This is different from previous simulations, where the bipolar pattern of Hall reconnection was suggested.