Assessment of time-series of troposphere zenith delays derived from the Global Data Assimilation System numerical weather model

Troposphere zenith path delays derived from the Global Data Assimilation System (GDAS) numerical weather model (NWM) are compared with those of the International GNSS Service (IGS) solutions over a 1.5-year period at 18 globally distributed IGS stations. Meteorological parameters can be interpolated from the NWM model at any location and at any time after December 2004. The meteorological parameters extracted from the NWM model agree with in situ direct measurements at some IGS stations within 1 mbar for pressure, 3° for temperature and 13% for relative humidity. The hydrostatic and wet components of the zenith path delay (ZPD) are computed using the meteorological parameters extracted from the NWM model. The total ZPDs derived from the GDAS NWM agree with the IGS ZPD solutions at 3.0 cm RMS level with biases of up to 4.5 cm, which can be attributed to the wet ZPDs estimates from the NWM model, considering the less accurate interpolated relative humidity parameter. Based on this study, it is suggested that the availability and the precision of the GDAS NWM ZPD should be sufficient for nearly all GPS navigation solutions.

Assessment of runoff,water and sediment quality in the Selenga River basin aided by a web-based geoservice

The Selenga River is the main artery feeding Lake Baikal. It has a catchment of ~450000 km² in the boundary region between Northern Mongolia and Southern Siberia. Climate, land use and dynamic socioeconomic changes go along with rising water abstractions and contaminant loads originating from mining sites and urban wastewater. In the future, these pressures might have negative impacts on the ecosystems of Lake Baikal and the Selenga River Delta, which is an important wetland region in itself and forms the last geobiochemical barrier before the Selenga drains into Lake Baikal. The following study aims to assess current trends in hydrology and water quality in the Selenga-Baikal basin, identify their drivers and to set up models (WaterGAP3 framework and ECOMAG) for the prediction of future changes. Of particular relevance for hydrological and water quality changes in the recent past were climate and land use trends as well as contaminant influx from mining areas and urban settlements. In the near future, additional hydrological modifications due to the construction of dams and abstractions/water diversions from the Selenga’s Mongolian tributaries could lead to additional alterations.     

Types of river channel patterns and their natural controls

River channel patterns are thought to form a morphological continuum. This continuum is two-dimensional, defined by plan features of which there are three (straight, meandering, branching), and structural levels of fluvial relief of which there are also three (floodplain, flood channel, low-water channel). Combinations of these three categories define the diversity of patterns. One of the most important factors in channel development is stream power, defined by water discharge and river slope. The greater the stream power, the stronger the branching tendency, but threshold values of stream power are different for the three different hierarchical levels of channel relief. The critical stream power values and hydrological regime together define the channel pattern, and analysis of the pattern type can be undertaken using effective discharge curves. © 1998 John Wiley & Sons, Ltd.     

On Continuous Observations of Thin Walls of High-Density Plasma in the High-Latitude Ionosphere from <Emphasis Type="Italic">Arktika-M</Emphasis> Satellites

A new structure element of the Arctic ionosphere has been detected from the data of topside sounding of the ionosphere: quasi-vertical walls of high-density plasma. The importance of studying this phenomenon for geophysics and the practice of radio wave propagation in high latitudes is noted. The Arktika-M hydrometeorological space complex with an onboard ionosonde is proposed for its study. The possibility of observing and analyzing all life-cycle phases of this ionospheric inhomogeneity is shown.     

Eruptive Instability of the Magnetic-Flux Rope: Gravitational Force and Mass-Unloading

We investigate the coronal imaging capabilities of the Solar UltraViolet Imager (SUVI) on board the Geostationary Operational Environmental Satellite-R series spacecraft. Nominally Sun-pointed, SUVI provides solar images in six extreme ultraviolet (EUV) wavelengths. On-orbit data indicated that SUVI had sufficient dynamic range and sensitivity to image the corona to the largest heights above the Sun to date while simultaneously imaging the Sun. We undertook a campaign to investigate the existence of the EUV signal well beyond the nominal Sun-centered imaging area of the solar EUV imagers. We off-pointed the SUVI line of sight by almost one imaging area around the Sun. We present the details of the campaign we conducted when the solar cycle was at near the minimum and some results that confirm that EUV emission is present to beyond three solar radii.

     

Undersampling in action and at scale: application to the COVID-19 pandemic

Stochastic Environmental Research and Risk Assessment - It is the purpose of this short communication to analyze the possible caveats in the statistical interpretation of collected data,...     

A Methodology for Quantifying Uncertainty in Climate Projections

Possible climate change caused by an increase ingreenhouse gas concentrations, despite having been asubject of intensive study in recent years, is stillvery uncertain. Uncertainties in projections ofdifferent climate variables are usually described onlyby the ranges of possible values. For assessing thepossible impact of climate change, it would be moreuseful to have probability distributions for thesevariables. Obtaining such distributions is usuallyvery computationally expensive and requires knowledgeof probability distributions for characteristics ofthe climate system that affect climate projections. A fewstudies of this kind have been carried out with energybalance/upwelling diffusion models. Here wedemonstrate a methodology for performing a similarstudy with a 2 dimensional (zonally averaged) climatemodel that reproduces the behavior of coupledatmosphere/ocean general circulation models morerealistically than energy balance models. Thismethodology involves application of the DeterministicEquivalent Modeling Method to derive functionalapproximations of the model's probabilistic response.Monte Carlo analysis is then performed on theapproximations. An application of the methodology isdemonstrated by deriving the uncertainty in surfaceair temperature change and sea level rise due tothermal expansion of the ocean that result fromuncertainties in climate sensitivity and the rate ofheat uptake by the deep ocean for a prescribedincrease in atmospheric CO₂ concentration. Wealso demonstrate propagation of correlateduncertainties through different models, by presentingresults that include uncertainty in projected carbonemissions.     

Statistical description of the Black Sea near-surface circulation using drifters in 1999–2003

The near-surface circulation in the Black Sea is studied with the data of 54 satellite-tracked drifters in the period 1999–2003. The drifter trajectories confirm the prevalence of the Rim Current trapped on the continental slope (between water depths of 400 and 1800 m) along the periphery of the basin where sub-inertial speeds can reach 1 m/s. Some drifters were found to complete an entire basin loop with the Rim Current in 90–180 days. Meanders and loops in the tracks prove the existence of mostly anticyclonic circulation features inshore of the Rim Current, including strong signatures of the Batumi and Sevastopol eddies. They also reveal the presence of cyclonic and anticyclonic currents in most areas of the Black Sea. Pseudo-Eulerian statistics (averaged in 50-km bins), that is, mean currents and the corresponding velocity variances, show a strong and highly fluctuating signature of the Rim Current and the enhanced variability associated with the Batumi and Sevastopol eddies. The latter is also collocated with the branching of the Rim Current southwest of the Crimean Peninsula. It is shown that the kinetic energy is mainly in the mean for the Rim Current and in the velocity fluctuations elsewhere. Seasonal variability is also explored. The Rim Current tends to form a stronger single loop trapped on the continental slope in winter/spring, whereas in summer/fall the mean circulation is more meandering, recirculation cells appear in the central areas and the bifurcation southwest of Crimea is enhanced. There is some evidence of the reversal of sense of rotation of the currents in the Batumi Eddy region, changing from mainly anticyclonic in summer/fall to cyclonic in winter/spring. Mean residence times were calculated in the 50-km bins, with values ranging from a few days in the central basin to 8 days in the northwestern coastal area. Globally, the kinetic energy levels were found higher in winter–spring and lower in summer–fall, with a significant maximum in March. Single-particle Lagrangian statistics were computed for the entire basin, for the two extended seasons, and in selected local areas. Velocity variance, diffusivity and Lagrangian integral time scales are generally larger in the zonal direction. Globally, the velocity variance is 174 and 127 cm²/s² in the zonal and meridional directions, respectively, after the removal of the pseudo-Eulerian mean circulation. For the zonal direction, a diffusivity value of 4.5×10⁷ cm²/s and Lagrangian integral time and space scales of 3 days and 34 km were found. For the meridional direction, these statistics amount to 4.5×10⁷ cm²/s, 1.2 days and 12.2 km. Seasonal and geographical variations of these Lagrangian statistics were also assessed, showing variations between 1.9 (0.9) 10⁷ and 8.3 (2.0) 10⁷ cm²/s for the diffusivity in the zonal (meridional) direction. Integral time and space scales vary between 1 and 4.7 days, and 8.8 and 58 km, respectively. Seasonal differences are significant only in the zonal direction, where the diffusivity increases from 3.1×10⁷ to 5.9×10⁷ cm²/s and the integral scales vary from 2.1 days (24 km) to 3.8 days (44 km) from summer/fall to winter/spring.