Tumulus development on lava flows: insights from observations of active tumuli and analysis of formation models

Here, we use observations of active flows along with detailed morphometric field measurements of more than 70 tumuli on flows at Mount Etna (Italy), Kilauea, and Hualalai (US) volcanoes to constrain a previously published model that estimates the pressure needed to form tumuli. In an attempt to discover the nature and magnitude of pressure variations within active lava flow interiors, we then consider how tumuli differ from idealized circular plates. We incorporate observations of active tumuli and find that they may grow asymmetrically yet produce a symmetrical tumulus and can form where the flow path significantly changes direction. Bending models of clamped edges provide the most reasonable head estimates for the tumuli in our study. Tumulus formation requires the proper combination of cooling and effusion rate. If cooling is too extensive and effusion rate too low, the crust will provide too much resistance to bending. If cooling is too limited and effusion rates too high, crusts will not develop or have insufficient strength to resist fracture and subsequent breakouts. We do not find it surprising that tumuli are rarely found over well-established lava tubes that typically have rigid, walls/overlying crusts that exceed 2 m in thickness and provide too much resistance to bending. Silicic flows lack tumuli because the viscosity gradients within the flow are insufficient to concentrate stress in a localized area.     

Using a landform evolution model to study ephemeral gullying in agricultural fields: the effects of rainfall patterns on ephemeral gully dynamics

Water driven soil erosion is a major cause of land degradation worldwide. Ephemeral gullies (EGs) are considered key contributors to agricultural catchment soil loss. Despite their importance, the parameters and drivers controlling EG dynamics have not been adequately quantified. Here we investigate the effects of rainfall characteristics on EGs, using the physically based landform evolution model (LEM) CAESAR‐Lisflood. An initial goal of this study was to test the feasibility of using a LEM to estimate EG dynamics based on an easily obtainable and moderate spatial resolution (2 × 2 m) Digital Elevation Model (DEM). EG evolution was simulated for two rainfall seasons in a 0.37 km² agricultural plot situated in a semiarid catchment in central Israel. The 2014 rainfall season was used to calibrate the model and the 2015 season was used for validation. The model overall well predicted the EG network structure and average depth but tended to underestimate the EG length. The effects of rainfall characteristics on EG dynamics were investigated by comparing simulations employing seven rainfall scenarios. Four of these scenarios differ in their overall rainfall volume relative to observed precipitation (+20%, +10%, ?10%, ?20%). The remaining three scenarios vary in the temporal distribution of rainfall during each storm, allowing us to isolate the effect of rainfall intensity on EG evolution. The results show that: (1) EG dynamics strongly correlated with changes in rainfall volume; (2) small‐scale morphological behavior varies between rainfall scenarios, resulting in different meandering and connectivity variability; (3) EG evolution is divided into two main stages, an initial rapid development occurring after the first two weeks of the rainy season, followed by a stable development period; (4) a 12 mm h^?1 intensity threshold was observed to initiate and, later, modify EGs; and (5) inner storm rainfall variability can have a considerable effect on EG evolution. Copyright © 2016 John Wiley & Sons, Ltd.     

Model prediction capacity of ephemeral gully evolution in conservation tillage systems

Ephemeral gully (EG) erosion has an important impact on agricultural soil losses and increases field surface hydrology connectivity and transport of pollutants to nearby water bodies. Watershed models including an EG component are scarce and not yet properly evaluated. The objective of this study is to evaluate the capacity of one such tool, AnnAGNPS, to simulate the evolution of two EG formed in a conservation tillage system. The dataset for model testing included runoff measurements and EG morphological characteristics during 3 years. Model evaluation focused on EG evolution of volume, width, and length model outputs, and included calibration and testing phases and a global sensitivity analysis (GSA). While the model did not fully reproduce width and length, the model efficiency to simulate EG volume was satisfactory for both calibration and testing phases, supporting the watershed management objectives of the model. GSA revealed that the most sensitive factors were EG depth, critical shear stress, headcut detachment exponent coefficient b, and headcut detachment leading coefficient a. For EG outputs the model was additive, showing low sensitivity to interactions between the inputs. Prediction of EG spatial evolution on conservation tillage systems requires improved development of gully erosion components, since many of the processes were developed originally for traditional tillage practices or larger channel systems. Our results identify the need for future research when EG form within conservation tillage systems, in particular to study gully headcut, soil erodibility, and width functions specific to these practices.     

Spatio-temporal evolution of Yellowstone deformation between 1992 and 2009 from InSAR and GPS observations

In this study, the spatio-temporal evolution of Yellowstone deformation between 1992 and 2009 is monitored using interferometric synthetic aperture radar (InSAR) data acquired by the European Remote-Sensing Satellites (ERS-1 and ERS-2) and the Environmental Satellite (ENVISAT). These data are combined with continuous global positioning system (GPS) measurements to identify four discrete episodes of caldera subsidence and uplift, these episodes are: 1992–1995 (subsidence of 2.7 cm/year), 1996–2000 (subsidence of 0.5 cm/year, with local uplift of 1.7 cm/year at Norris), 2000–2004 (subsidence of 0.7 cm/year, with local uplift of 0.6 cm/year at Norris), and 2004–2009 (uplift of 3–8 cm/year, with local subsidence of 1–4 cm/year at Norris). We construct the full three-dimensional velocity field of Yellowstone deformation for 2005–2006 from ascending and descending ENVISAT orbits. The InSAR three-dimensional velocity field and three-component GPS measurements indicate that the majority of the observed deformation (3–8 cm/year) across the Yellowstone caldera and near Norris Geyser Basin (NGB) occurred in the vertical direction between the summers of 2005 and 2006. During this time, significant lateral displacements of 3–7 cm/year also occurred in the east–west direction at the southeastern and western rims of the Yellowstone caldera and in the area between Hebgen Lake and NGB. Minor north–south displacements of about 0.2 cm/year also occurred, however, in the southwestern section of the caldera and near Yellowstone Lake during the same period. The calculated three-dimensional velocity field for 2005–2006 implies the existence of two pressure-point sources, beneath the two structural resurgent domes in the Yellowstone caldera, connected by a planar conduit, rather than a single, large sill as proposed in previous studies. Furthermore, no measurable displacements occurred along any fault zone across the caldera during the entire period of observation (1992–2009). Therefore, we infer that magmatic and hydrothermal processes beneath the Yellowstone caldera and NGB were the main sources of deformation.     

Microwave radiation of solar active regions before X flares according to the RATAN-600 observations in 2011

The evolution of the microwave radiation from four active regions, where strong X-ray flares (X-class, GOES) occurred in 2011, has been studied. Daily multiwavelength RATAN-600 radio observations of the Sun in the 1.6–8.0 cm range have been used. It has been indicated that the radiosource above the photospheric magnetic field neutral line (above the region with the maximal convergence of the fields opposite in sign) becomes predominant in the structure of the active region microwave radiation one to two days before a powerful flare as in the eruptive events previously studied with RATAN-600. The appearance of such a radiosource possibly reflects the current sheet formation in the corona above the active region. The energy necessary for a flare is stored in the magnetic field of active region, which can be considered as a factor for predicting a powerful flare.     

Studying the solar corona above active regions from microwave observations during solar flares recorded by CORONAS-F satellite

In 2001–2003, 45 flares of hard X ray (HXR) and gamma ray radiation, identified with a particular active region (AR) that produced each event, were recorded during the experiments onboard the Russian Solar Observatory CORONAS-F using the SONG (solar neutrons and gamma ray quanta) instrument. The solar corona structure and dynamics above these ARs is studied on the basis of the microwave observations with two Russian radio telescopes RATAN-600 and Siberian Solar Radio Telescope (SSRT). The results are illustrated using the active region NOAA 9601 and flare of September 5, 2001 (～ 1430 UT) as an example. The flare is interesting because the energy of its gamma radiation exceeded 1 MeV, while its power was only M6.0 in soft X rays. Such a combination of the event characteristics is not too frequent, which indicates that the spectrum of the studied event was rather hard. The type of the source of microwave radiation above NOAA 9601 has been determined. Some properties of this-type sources of a diagnostic value for detecting ARs capable of producing HXR and gamma radiation are indicated.     

Comparison of Clark,Nash Geographical Instantaneous Unit Hydrograph models for semi arid regions

This paper compares the results obtained from three hydrologic techniques namely Clark, Nash and Geographical Instantaneous Unit Hydrograph. Underpinning of these models and calibration of parameters for these models was a demanding assignment which was performed by downhill simplex optimization method. A semi-arid region of Pakistan was selected for testing the models. Computer coding was prepared for all the models. SPOT maps of the study area were collected from NESPAK (National Engineering Services of Pakistan). The rainfall runoff data was taken from Punjab Irrigation and Power Department. The maps were digitized using ERDAS and Arc GIS to determine the geographic parameters of the watershed. Field surveys and measurements were used to estimate the discharge data. The shape of direct runoff hydrograph, peak flows and time to peak flow obtained from the three models were compared. The model efficiency was determined by a statistical parameter coefficient of determination. It was found that the Clark model simulated superior results in comparison with Nash and Geographical Instantaneous Unit Hydrograph models.     

山基GPS掩星与自动气象站观测结果比较

山基GPS掩星技术可以精确获得低层大气折射率信息,其观测原理是:在高山的山顶安装GPS接收机,跟踪GPS卫星的低仰角和负仰角信号,通过载波相位的变化求出大气折射造成的弯曲角剖面,从而利用科学反演方法获得观测点高度以下的大气折射率剖面.为了对山基掩星测量数据进行验证,2005年8月1日～29日,在河北雾灵山(40.60°N,117.48°E,2118m)开展了为期一个月的山基GPS掩星观测与其他探测的时比实验.实验所用的JAVAD双频GPS接收机共工作576小时,接收机朝南观测,记录到山基掩星事件1136次,其中上升掩星621次,下降掩星515次.实验期间,在雾灵山顶利用自动气象观测仪每天24小时观测当地的温度、湿度和气压,由此可计算大气折射率.本文利用雾灵山GPS掩星实验所获得的观测数据,成功反演得到大气折射率剖面,并将所得接收机高度的折射率与雾灵山顶自动气象站观测结果进行比对,分析结果表明:山基GPS掩星和自动气象站观测结果是一致的.山基GPS掩星观测可为低层大气环境监测提供大量数据,具有潜在的应用前景.     

Gully erosion in the Siwalik Hills,Nepal: estimation of sediment production from active ephemeral gullies

A simple field‐based monitoring programme was established in a small catchment (area 4·6 km²) to find the rates of gully erosion in the Siwalik Hills, Nepal. The rates are used to estimate the amount of sediment produced by gully erosion in the catchment. Three large and active gullies were selected with areas ranging from 0·44 to 0·78 ha. Aerial photographs taken in 1964, 1978 and 1992 were ortho‐rectified and used to study the dynamics of gully heads. The same gullies were also monitored manually using an orthogonal reference system fixed by erosion pins around the gully heads. Results from the aerial photos indicated that the gullies expanded remarkably over the period from 1964 to 1992, by 34 to 58 per cent. Head‐retreat rates during that period were 0·48, 0·55 and 0·73 m a^?1 and average annual sediment evacuation was estimated as 2534 ± 171, 959 ± 60 and 2783 ± 118 m³ a^?1 for the three gullies respectively. From the field measurement, estimated volumes were found to vary from 731 ± 57 to 2793 ± 201 m³ a^?1 over the monitoring period of two years. It was also found that the gullies produce sediment which accounts for up to 59 per cent of the sediment produced from surface erosion in the headwater catchment. The findings are useful for planning and executing appropriate control measures and constructing a sediment hazard map at the catchment scale. Copyright © 2006 John Wiley & Sons, Ltd.     

中国大陆及周边地区1900年以来的地震活动特征

根据中国大陆及周边地区１９００年以来Ｍ≥６．９级地震资料,着重分析地震活动的时空分布特征。结果表明：研究区地震活动具有分区,分期特征,整个时段可划分为３个活跃期（幕）、第Ⅰ、Ⅱ活跃幕持续时间分别在３９和３２年左右,第Ⅲ活跃幕已持续了２２年,目前尚未结束,还可能延续１０－１７年左右;在时空域内,地震活动出现了分区集中和地区间的交替迁移以及平静与活跃的交替现象。每个活跃幕内,地震活动以多周期轮回的迁移     

Some aspects of electrostatic coupling between E and F regions relevant to plasma irregularities: A review based on recent observations

This paper provides a review on some of the electrostatic coupling effects relevant for generating/modifying plasma irregularities during nighttime in the low latitude ionosphere based on recent observations. Emphasis is given to the role of large polarization electric field associated with an unstable region affecting another region remotely located. Recent radar observations on valley region and E region irregularities from low latitudes show convincing evidence in support of effective electrostatic field coupling along the magnetic field line for their manifestation. Interestingly, the low latitude observations clearly show the ineffectiveness of plasma bubble related fringe fields in generating low latitude valley region irregularities unlike that over the dip equator. Velocity perturbations associated with the unstable low latitude E region relevant for studying the seeding of equatorial spread F are also shown. These new observations have been critically examined in the light of existing experimental knowledge and current understanding of the electrostatic coupling effects for the generation/modification of plasma irregularities in a remote region.     

Comparison between two theoretical mechanisms for the formation of the plasmapause and relevant observations

The plasmapause formation physical mechanisms are recalled: (i) the MHD convection mechanism, based on the original idea that the plasmapause coincides with the last closed equipotential (LCE) of the magnetospheric convection electric field or with the last closed streamline (LCS) of the equatorial plasma, and (ii) the interchange mechanism, which is based on peeling off the plasmasphere as a result of substorm associated enhancements of the night side convection velocity, leading to an enhanced centrifugal acceleration in the outermost layers of the plasmasphere. The plasmapause positions, predicted by these alternative theories, were numerically determined for two different magnetospheric empirical electric field models: (i) the Volland-Stern-Maynard-Chen (VSMC) and (ii) McIlwain E5D models, both of which are Kp-dependent. The predicted positions and overall shape of the equatorial plasmapause cross-sections are confronted to those derived from decades of whistler and satellite observations including the EUV observations during the substorm of June 27, 2001. It is found that the VSMC electric field model and the LCS plasmapause formation theory less correspond to whistler measurements and in-situ satellite observations than the E5D model and the interchange plasmapause formation mechanism. Published in Russian in Geomagnetizm i Aeronomiya, 2008, Vol. 48, No. 5, pp. 579–597. The article was translated by the authors.     

Harmonizing models and observations: Data assimilation in Earth system science

Models and observations are two fundamental methodological approaches in Earth system science(ESS). They evolve collaboratively and enhance one another. However, neither of these two approaches is perfect, and they have incompatibilities due to their methodological differences. The emergence of data assimilation(DA) has enabled these two approaches to develop in conjunction and form a harmonic ESS methodology. As a result, DA has shown a fresh vitality and applicability in ESS. This paper reviews the application of DA in the main branches of ESS, traces the coordinated evolution of DA with the methodologies of rationalism and empiricism, analyzes the relationships of DA with estimation theory and cybernetics, summarizes the advances of DA in China, and presents an outlook on the challenges facing the development of a uniform DA for ESS. DA theories and methods will continue to evolve and provide an increasingly mature methodology for enhancing the understanding and prediction of Earth as a system.     

Variations in fractal characteristics of active regions and flares

A multifractal analysis of the Hα images for an active region has been performed; the singularity spectra and segmented images for a narrow range of fractal dimensions have been computed for them. The segmented images show the presence of singular areas where the singularity index takes on maximum values. These areas mark the active sites of flares.     

Comparison between inelastic earth models constructed from astrometric and tidal gravity data

As was shown in [Molodensky, 2004a, 2004b], modern very long base interferometer (VLBI) data on the amplitudes and phases of the Earth’s forced nutation can provide significantly more rigid constraints on possible values of the quality factor of the lower mantle Q _μ and on the dynamic flattening of the liquid core e _lc as compared with seismic evidence and data on damping of the free oscillations of the Earth. On the other hand, the accuracy of modern tidal gravity data (obtained from twenty-year series of observations with a cryogenic gravimeter) is also very high and these data must be taken into account while estimating the parameters Q _μ and e _lc . The paper presents comparative estimates of the determination accuracy of the parameters Q _μ and the dynamic flattening of the liquid core from VLBI and the aforementioned tidal gravity data.     

History of kinetic polar wind models and early observations

Both the polar and solar winds were postulated to explain observations made before routine access to space was possible. Subsequently, significant limitations of the thermal plasma observations of the polar wind led to diverging approaches to modeling it. The hydrodynamic and kinetic approaches to modeling were able to explain the limited observational data. With no extensive and robust data set to determine the relative importance of dynamical effects in the ionosphere and convection in the magnetospheric electric field, there was no valid way to choose between the competing approaches. This has caused confusion in the space and plasma physics communities regarding the polar wind. Recent polar wind observations from the Japanese Akebono, NASA Polar, and the upcoming Canadian e-POP missions call for an appropriate and timely review of our current understanding of the polar wind. This paper presents a review of the modeling techniques from the earliest primitive approaches to the most current treatments that account for collision processes, non-Maxwellian distributions of multiple ion species, the role of photoelectrons in controlling plasma outflow and other topics. A brief overview of early polar wind measurements is given in Appendix B.