Modeling studies of the bioluminescence potential dynamics in a high Arctic fjord during polar night

Ocean Dynamics - During polar nights in January 2012 and 2017, significantly higher bioluminescence (BL) potential emissions in the upper 50 m were observed in the fjord Rijpfjorden...     

Indexing the relationship between polar motion and water mass change in a giant river basin

Previous studies on the relationship between polar motion and water mass change have mainly concentrated on the excitation of polar motion via global terrestrial water storage changes(TWSC). In view of the uneven distribution of global terrestrial water storage, the relationship between regional water mass change and polar motion needs to be further explored owing to the lack of documented results. In addition, given the uncertainty in the estimation of TWSC, it is required to develop appropriate indices to describe water mass change from different perspectives. The Amazon River basin(referred to Amazon hereafter), containing the world's largest river, located at around the 90°W longitude, is selected as the study area. Water vapor flux, precipitation, runoff and TWSC are selected as the indices of water mass changes to reveal the relationship between polar motion and water mass change in this giant basin. The Mann-Kendall(M-K) method, the accumulated anomaly analysis method and the curvature method are used to identify the abrupt change points; the least squares method is used to estimate the trends,and the Fast Fourier Transform(FFT) and the Ensemble Empirical Mode Decomposition(EEMD) are used to perform a periodic analysis, for all the above indices. It is shown that, of all the indices from 1948 to 2011, water vapor flux is the most closely related index to polar motion. In detail, precipitation and water vapor flux contain beat periods of polar motion; water vapor flux,precipitation and polar motion have a common M-K test abrupt change point(occurring in ca. 1968) at the 0.05 significance level; water vapor flux has a similar accumulated anomaly curve with that of polar motion; and water vapor flux is more highly correlated with polar motion than most other indexes. It is found, just like global TWSC, the χ2 component of the excitation via water vapor flux and water storage change in the Amazon follows that of observed polar motion; χ1 does not follow. However, the pattern in the Amazon that the χ2 component of the excitation by water follows that of observed polar motion is at a more significant level than in global. Finally, the new index termed Location of Vapor-based Inter Tropical Convergence Zone(LVITCZ) we proposed to describe the annual mean latitudinal location of water mass change shows a more close and visual relationship between water mass change and polar motion than other chosen indices do.     

Investigating potential future changes in surface water flooding hazard and impact

Surface water flooding (SWF) is a recurrent hazard that affects lives and livelihoods. Climate change is projected to change the frequency of extreme rainfall events that can lead to SWF. Increasingly, data from Regional Climate Models (RCMs) are being used to investigate the potential water-related impacts of climate change; such assessments often focus on broad-scale fluvial flooding and the use of coarse resolution (>12 km) RCMs. However, high-resolution (<4 km) convection-permitting RCMs are now becoming available that allow impact assessments of more localised SWF to be made. At the same time, there has been an increasing demand for more robust and timely real-time forecast and alert information on SWF. In the UK, a real-time SWF Hazard Impact Model framework has been developed. The system uses 1-km gridded surface runoff estimates from a hydrological model to simulate the SWF hazard. These are linked to detailed inundation model outputs through an Impact Library to assess impacts on property, people, transport, and infrastructure for four severity levels. Here, a set of high-resolution (1.5 km and 12 km) RCM data has been used as input to a grid-based hydrological model over southern Britain to simulate Current (1996–2009) and Future (~2100s; RCP8.5) surface runoff. Counts of threshold-exceedance for surface runoff and precipitation (at 1-, 3- and 6-hr durations) are analysed. Results show that the percentage increases in surface runoff extremes, are less than those of precipitation extremes. The higher-resolution RCM simulates the largest percentage increases, which occur in winter, and the winter exceedance counts are greater than summer exceedance counts. For property impacts, the largest percentage increases are also in winter; however, it is the 12-km RCM output that leads to the largest percentage increase in impacts. The added-value of high-resolution climate model data for hydrological modelling is from capturing the more intense convective storms in surface runoff estimates.     

Variations in the near-ground electric field at high latitudes and the potential drop across the polar cap during morning polar substorms

This paper studies time variations in the near-ground atmospheric electric field (Ez) at the geomagnetic latitude of 74° (Hornsund observatory) during polar substorms. Ez variations are compared with those in the potential drop across the polar cap (Up), according to SuperDARN radar observations. It is found that in the morning sector, time variations in Ez are strongly driven by time variations in the electrojet and almost do not depend on time variations in Up, which is presumably due to the penetration of the electric field of the electrojet into tropospheric altitudes.     

Estimating potential evapotranspiration without continuous daily data: possible errors and impact on water balance simulations

Abstract

Alternative approaches to estimating monthly and annual potential evapotranspiration (PE) are explored in cases where daily climate data are not routinely recorded. A database consisting of data from 222 weather stations, representing a wide variety of climatic conditions, is used to draw general conclusions. In addition, two PE formulae with different data requirements are used: the standard FAO-56 Penman-Monteith equation, and a simple temperature-based equation. First, we tested the degree of bias introduced by using climate data averaged over long time periods instead of daily data. Second, we explored the sensitivity of PE estimation with respect to variations in sampling frequency of climate variables. The results show that using mean weather data has only a limited effect on monthly and annual PE estimates. Conversely, imperfect sampling of weather data may bias monthly and to a lesser extent annual PE estimates if the sampling period exceeds 5 and 10 days, respectively. Finally, we tested the impact of erroneous weather data on the simulations of annual actual evapotranspiration obtained with the Budyko model. The impact on the Budyko model outputs depends more on the dryness index of a given location than on annual PE; for regions under water stress, the errors in estimation of actual evapotranspiration are very limited, compared to humid regions where available energy is the dominating factor and the propagation of PE errors is important.

Citation Oudin, L., Moulin, L., Bendjoudi, H. & Ribstein, P. (2010) Estimating potential evapotranspiration without continuous daily data: possible errors and impact on water balance simulations. Hydrol. Sci. J. 55(2), 209–222.     

Eddy-permitting simulations of the sub-polar North Atlantic: impact of the model bias on water mass properties and circulation

Some previous studies demonstrated that model bias has a strong impact on the quality of long-term prognostic model simulations of the sub-polar North Atlantic Ocean. Relatively strong bias of water mass characteristics is observed in both eddy-permitting and eddy-resolving simulations, suggesting that an increase of model resolution does not reduce significantly the model bias. This study is an attempt to quantify the impact of model bias on the simulated water mass and circulation characteristics in an eddy-permitting model of the sub-polar ocean. This is done through comparison of eddy-permitting prognostic model simulations with the results from two other runs in which the bias is constrained by using spectral nudging. In the first run, the temperature and salinity are nudged towards climatology in the whole column. In the second run, the spectral nudging is applied in the surface 30 m layer and at depths below 560 m only. The biases of the model characteristics of the unconstrained run are similar to those reported in previous eddy-permitting and eddy-resolving studies. The salinity in the surface and intermediate waters of the Labrador Sea waters increases with respect to the climatology, which reduces the stability of the water column. The deep convection in the unconstrained run is artificially intensified and the transport in the sub-polar gyre stronger than in the observations. In particular, the transport of relatively salty and warm Irminger waters into the Labrador Sea is unrealistically high. While the water mass temperature and salinity in the run with spectral nudging in the whole column are closest to the observations, the depth of the winter convection is underestimated in the model. The water mass characteristics and water transport in the run with spectral nudging in the surface and deep layers only are close to observations and at the same time represent well the deep convection in terms of its intensity and position. The source of the bias in the prognostic model run is discussed.     

Modeling the water resources of the Black and Mediterranean Sea river basins and their impact on regional mass changes

For the first time, a dedicated release of the hydrology and water use model WaterGAP3, has been developed to spatially explicit calculate hydrological fluxes within river basins draining into the Mediterranean and Black Sea. The main differences between the new regional version of the global WaterGAP3 model and the previously applied global version WaterGAP2 can be found in the spatial resolution, snow modeling, and water use modeling. Comparison with observations shows that WaterGAP3 features a more realistic representation of modeled river runoff and inflow into both seas. WaterGAP3 generates more inflow to both seas than WaterGAP2. In the WaterGAP3 simulation, contributions to the total runoff into the Black Sea from individual discharge regions show in general a good agreement to climatology derived runoff, but lesser importance of Georgian rivers for the basin's water. After the successful model validation WaterGAP3 has been applied to correct estimates of seawater mass derived from the GRACE gravity mission and to account for freshwater inflow into both basins. The performance of the WaterGAP3 regional solution has been evaluated by comparing the seawater mass derived from GRACE corrected for the leakage of continental hydrology, to an independent estimate derived from steric-corrected satellite altimetry with steric correction from regional oceanographic models. The agreement is higher in the Mediterranean Sea than in the Black Sea. Results using WaterGAP3 and WaterGAP2 are not significantly different. However the agreement with the altimetry-derived results is higher using WaterGAP2, due to the smaller annual amplitude of the continental hydrology leakage from WaterGAP3. We conclude that the regional model WaterGAP3 is capable of realistically quantifying water mass variation in the region, further developments have been identified.     

Assessment of terrestrial water contributions to polar motion from GRACE and hydrological models

The hydrological contribution to polar motion is a major challenge in explaining the observed geodetic residual of non-atmospheric and non-oceanic excitations since hydrological models have limited input of comprehensive global direct observations. Although global terrestrial water storage (TWS) estimated from the Gravity Recovery and Climate Experiment (GRACE) provides a new opportunity to study the hydrological excitation of polar motion, the GRACE gridded data are subject to the post-processing de-striping algorithm, spatial gridded mapping and filter smoothing effects as well as aliasing errors. In this paper, the hydrological contributions to polar motion are investigated and evaluated at seasonal and intra-seasonal time scales using the recovered degree-2 harmonic coefficients from all GRACE spherical harmonic coefficients and hydrological models data with the same filter smoothing and recovering methods, including the Global Land Data Assimilation Systems (GLDAS) model, Climate Prediction Center (CPC) model, the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis products and European Center for Medium-Range Weather Forecasts (ECMWF) operational model (opECMWF). It is shown that GRACE is better in explaining the geodetic residual of non-atmospheric and non-oceanic polar motion excitations at the annual period, while the models give worse estimates with a larger phase shift or amplitude bias. At the semi-annual period, the GRACE estimates are also generally closer to the geodetic residual, but with some biases in phase or amplitude due mainly to some aliasing errors at near semi-annual period from geophysical models. For periods less than 1-year, the hydrological models and GRACE are generally worse in explaining the intraseasonal polar motion excitations.     

Intentional contamination of water distribution networks: developing indicators for sensitivity and vulnerability assessments

Performing a comprehensive risk analysis is primordial to ensure a reliable and sustainable water supply. Though the general framework of risk analysis is well established, specific adaptation seems needed for systems such as water distribution networks (WDN). Understanding of vulnerabilities of WDN against deliberate contamination and consumers’ sensitivity against contaminated water use is very vital to inform decision-maker. This paper presents an innovative step-by-step methodology for developing comprehensive indicators to perform sensitivity, vulnerability and criticality analyses in case of absence of early warning system (EWS). The assessment and the aggregation of these indicators with specific fuzzy operators allow identifying the most critical points in a WDN. Intentional intrusion of contaminants at these points can potentially harm both the consumers as well as water infrastructure. The implementation of the developed methodology has been demonstrated through a case study of a French WDN unequipped with sensors.     

Solomon Sea circulation and water mass modifications: response at ENSO timescales

The South Pacific low latitude western boundary currents (LLWBCs) carry waters of subtropical origin through the Solomon Sea before joining the equatorial Pacific. Changes in their properties or transport are assumed to impact El Niño Southern Oscillation (ENSO) dynamics. At ENSO timescales, the LLWBCs transport tends to counterbalance the interior geostrophic one. When transiting through the complex geography of the Solomon Sea, the main LLWBC, the New Guinea Coastal Undercurrent, cannot follow a unique simple route to the equator. Instead, its routes and water mass properties are influenced by the circulation occurring in the Solomon Sea. In this study, the response of the Solomon Sea circulation to ENSO is investigated based on a numerical simulation. The transport anomalies entering the Solomon Sea from the south are confined to the top 250 m of the water column, where they represent 7.5 Sv (based on ENSO composites) for a mean transport of 10 Sv. The induced circulation anomalies in the Solomon Sea are not symmetric between the two ENSO states because of (1) a bathymetric control at Vitiaz Strait, which plays a stronger role during El Niño, and (2) an additional inflow through Solomon Strait during La Niña events. In terms of temperature and salinity, modifications are particularly notable for the thermocline water during El Niño conditions, with cooler and fresher waters compared to the climatological mean. The surface water at Vitiaz Strait and the upper thermocline water at Solomon Strait, feeding respectively the equatorial Pacific warm pool and the Equatorial Undercurrent, particularly affect the heat and salt fluxes. These fluxes can change by up to a factor of 2 between extreme El Niño and La Niña conditions.     

利用GPS对磁暴期间极区TEC变化与极区碎片（Polar Patches）的研究

利用2004年11月6～10日磁暴发生期间南极区域内的中国中山站GPS常年跟踪站（ZHON）和国际GPS服务站（CAS1, MCM4, SYOG, MAW1）的GPS观测数据,计算了可观测卫星传播路径上的TEC和ROT值,进而依据TEC的波动频率和幅度推估出极区碎片的个数,分析了极区磁暴期间电离层响应及其极区碎片特性. 最终所得TEC和ROT结果与极区地磁场Dst和Kp指数信息相吻合,如实地反映了磁暴事件和极区碎片的出现. 本文所做工作在国内尚未开展,因此所用方法和结论为将来这一方向的研究提供了一定的参考.     

1960—2019年鄱阳湖五河流域陆地水储量变化及其对主湖区水量的影响

流域内地表水、土壤水和地下水等水储量组分相互作用和影响,共同构成了陆地水储量(TWS)的动态变化格局。本文以GRACE卫星数据为基准,利用GLDAS数据解析1960-2019年鄱阳湖“五河”流域TWS的时空变化特征及各组分对其变化的贡献,采用相关分析方法分析TWS对降水的滞后响应关系,并进一步采用多元线性回归分析方法探究了“五河”流域TWS及各组分对鄱阳湖主湖区水量的影响。结果表明:“五河”流域年TWS在1960-2011年(P1)以-0.07 mm/a的下降,而在2012-2019年(P2)以3.37 mm/a的速率上升。相较于P1阶段,P2阶段春、夏季TWS盈余增强,秋、冬季TWS亏损减弱。春、夏季流域西部TWS变化逐渐由地表水转变为地下水储量主导,流域东部TWS变化主要由地下水储量主导;秋、冬季流域TWS变化主要为地下水储量主导,且地表水对TWS变化的贡献减弱。流域TWS对降水变化的响应滞时呈现夏、秋季短(1个月)而冬、春季长(3~6个月)的季节模式。地下水储量和土壤水对TWS变化的贡献增加会延长TWS对降水的响应滞时,而地表水对响应滞时起相反的作用。“五河”流域TWS与鄱阳湖主湖区水量具有显著的正相关性,地表水和地下水储量增加对湖区水体的增长具有正向作用,而土壤水增加对湖区水体的增长具有反向作用。本研究解析了近六十年鄱阳湖“五河”流域陆地水储量的变化及其对主湖区水量的影响,可为流域水安全管理提供参考。     

Response of the reconnection electric field and polar cap potential to the IMF and velocity of solar wind

It is well known that the cross polar cap potential is saturated under a strong interplanetary electric field and is often said to be related to the ionospheric currents. To investigate the other factors influencing this phenomenon, a global magnetohydrodynamics simulation not including the feedback from the ionosphere to the magnetosphere was conducted. The simulation results showed that an increase in the southward IMF causes a smaller increase in the cross polar cap potential than that caused by an increase in the solar wind velocity. This difference was caused by the transportation of reconnected magnetic field lines towards the tail.     

极点热层密度变化特征及其受太阳风扇形结构调制

本文基于2002年至2010年的GRACE卫星的观测密度统计分析南北极点的热层大气密度的世界时（即磁地方时）变化.研究发现：在9—11月份地球处于行星际磁场为背向太阳的扇区内（背向扇区）时,南极点热层密度在约17:00 UT（13:30 MLT）达到最大值,比日平均值高约22%;而在6—8月份,当地球处于行星际磁场为面向太阳的扇区内（面向扇区）时,北极点热层密度在06:00 UT（12:30 MLT）达到最大值,比日平均值高约13%.南极点的磁纬是-74°,其在15:30 UT处于磁地方时正午,恰与极尖区位置重合.北极点在5:30 UT处于磁地方时正午,此时北极点与极尖区位置最靠近.因此,极点热层大气密度的磁地方时变化可能是其周期性靠近极尖区的结果.南北极点热层密度的磁地方时变化分别在背向和面向扇区内更明显,这可能与行星际磁场B_y分量对南北半球密度的不同影响有关.统计结果还表明,极点热层大气密度的磁地方时变化在冬季半球内不明显.这可能是由于在冬季半球,沉降于极尖区的粒子相比夏季半球少、沉降高度低,因而能量沉降所引起的热层上部的密度增强较小.

     

Correlations of mesospheric variability and their relation to the large-scale circulation during polar winter

WINDII data from the Upper Atmosphere Research Satellite show an integrated OH emission rate systematically increasing with decreasing airglow peak altitude. A Spectral Airglow Temperature Imager (SATI) at 74°N shows strong positive correlations between the integrated emission rate and the rotational OH temperature. Taken together, the two correlations are consistent with vertical motions of the mesopause region, over periods from hours to winter to winter. SABER data are consistent with these correlations. The O₂ atmospheric band shows much weaker correlations. The SATI mesospheric temperatures also correlate with Resolute Bay temperatures for the 22.5 km level, a mesosphere–stratosphere relationship.     

Hydrodynamic dispersion during absorption of water by soil: 2. Immobile water model

The assumptions and analysis of Part 1 are extended to the three model soil-water profiles having different immobile-water contents up to 0.08 m³ m^?3. Concentration profiles in the mobile zone obtained with a constant dispersion coefficient are compared with those calculated with the same dispersion coefficient and no immobile water. The average concentration profiles were calculated from the concentration of the solution in both the mobile and immobile phases. Increasing the immobile-water content decreased and shifted the average concentration profiles further into the soil. The values of the dispersion coefficient calculated with the immobile-water fraction ignored, were found to be water content dependent and many times greater than that of the input dispersion coefficient.     

Impacts of forest conversion and agriculture practices on water pathways in Southern Brazil

Land‐use/cover change (LUCC), and more specifically deforestation and multidecadal agriculture, is one of the various controlling factors of water fluxes at the hillslope or catchment scale. We investigated the impact of LUCC on water pathways and stream stormflow generation processes in a subtropical region in southern Brazil. We monitored, sampled and analysed stream water, pore water, subsurface water, and rainwater for dissolved silicon concentration (DSi) and ¹⁸O/¹⁶O (δ¹⁸O) signature to identify contributing sources to the streamflow under forest and under agriculture. Both forested and agricultural catchments were highly responsive to rainfall events in terms of discharge and shallow groundwater level. DSi versus δ¹⁸O scatter plots indicated that for both land‐use types, two run‐off components contributed to the stream discharge. The presence of a dense macropore network, combined with the presence of a compact and impeding B‐horizon, led to rapid subsurface flow in the forested catchment. In the agricultural catchment, the rapid response to rainfall was mostly due to surface run‐off. A 2‐component isotopic hydrograph separation indicated a larger contribution of rainfall water to run‐off during rainfall event in the agricultural catchments. We attributed this higher contribution to a decrease in topsoil hydraulic conductivity associated with agricultural practices. The chemical signature of the old water component in the forested catchment was very similar to that of the shallow groundwater and the pore soil water: It is therefore likely that the shallow groundwater was the main source of old water. This is not the case in the agricultural catchments where the old water component had a much higher DSi concentration than the shallow groundwater and the soil pore water. As the agricultural catchments were larger, this may to some extent simply be a scale effect. However, the higher water yields under agriculture and the high DSi concentration observed in the old water under agriculture suggest a significant contribution of deep groundwater to catchment run‐off under agriculture, suggesting that LUCC may have significant effects on weathering rates and patterns.     

Influence of climate,water content and leaching on seasonal variations in potential water repellence

Seasonal variation in potential water repellence has not been widely reported in the literature, and little is known of the processes that cause changes in potential water repellence. In this study, the severity and stability of potential water repellence varied seasonally from being weakly hydrophobic in July 2009 (water drop penetration time, 0.19 min; water entry potential, 0.0 cm) to severely hydrophobic (water drop penetration time, 54 min; water entry potential, 14.3 cm) in May 2009. Seasonal variation in the stability of potential water repellence was significantly correlated with cumulative rainfall, air temperature and soil water deficit, which indicated that the accumulation of water‐repellent compounds, presumably polar waxes, resulted from microbial or plant inputs to the soil. Laboratory experiments demonstrated that saturating and mixing the soil resulted in a two to three order of magnitude reduction in the stability of potential water repellence, even after oven drying at 40 °C and 60 °C. Repeated leaching resulted in sequential reduction in both the stability and severity of water repellence. The significant correlation between soil water repellence and dissolved organic carbon content of the leachate, together with pedological evidence of organic staining of ped faces in the clay subsoil indicate that seasonal rainfall leached soluble water‐repellent compounds from the topsoil. The reestablishment of water repellence after saturation and leaching required the input of new water‐repellent compounds. These findings suggest that the use of surfactants before sowing may assist to leach water‐repellent compounds from the topsoil, allowing improved infiltration and reduced runoff through the remainder of the cropping season. Copyright © 2011 John Wiley & Sons, Ltd.     

水文干旱多变量联合设计及水库影响评估

基于东江流域博罗站月径流数据,采用游程理论提取水文干旱事件.选用Meta-Gaussian Copula函数,统计模拟水文干旱指标的多变量联合分布.采用Kendall联合重现期和最大可能权函数,设计给定联合超越重现期的水文干旱指标组合值,并定量评估水库径流调节作用对水文干旱多变量联合特征的影响.结果表明:东江流域水文干旱历时、强度和峰值的统计优选分布均为韦布尔分布.干旱指标之间具有较高的正相关性,Meta-Gaussian Copula能够很好地模拟水文干旱指标两变量和三变量联合分布.基于任意两个变量联合设计和三变量联合设计,干旱指标设计组合值位于同频位置附近,且同一个干旱指标设计值在不同变量组合之间差别较小.水库径流调节作用对于缓解东江流域水文干旱效果明显,同一组干旱指标的多变量联合超越重现期在水库影响下明显变大.联合超越重现期越小,水库对联合设计值的影响程度越大.根据目前水库运行模式,若要满足河道内最小管理流量目标,联合超越重现期10 a一遇的干旱历时、强度和峰值依然达到了约3.89~4.04月、7.20~7.97亿m3和2.99~3.12亿m3.