Annual Amplitude Research Articles

Slow-growing reef corals as climate archives: A case study of the Middle Eocene Climatic Optimum 40 Ma ago.

The skeletons of stony corals on tropical shallow-water reefs are high-resolution climate archives. However, their systematic use for unlocking climate dynamics of the geologic past is limited by the susceptibility of the porous aragonite skeleton to diagenetic alterations. Here, we present oxygen and carbon isotope time series (monthly resolution) from reef corals with an unusual unaltered preservation from the Middle Eocene Climatic Optimum (MECO) “hyperthermal” (40 million years ago). Annual extension of the corals at the studied midlatitude site (France) was remarkably low (0.2 cm). Nonetheless, isotope signatures display no evidence for kinetic disequilibria that discredit their use as climate archive, but growth rate–dependent annual signal amplitude attenuations need corrections using an innovative sampling approach. Thereafter, we present evidence of symbiotic zooxanthellae in reef corals of the Paleogene and subdued sea surface temperature seasonality of only 7° to 8°C during the MECO, consistent with the globally equant climate of the hothouse.

Analysis of mass flux variations in the southern Tibetan Plateau based on an improved spatial domain filtering approach for GRACE/GRACE-FO solutions

ABSTRACT Limited by the north-south stripes and noise, it is challenging to estimate mass flux variations with high-precision from the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) solutions. To extract more geophysical signals from the GRACE/GRACE-FO spherical harmonic coefficients (SHCs), we developed an improved spatial domain filtering (ISDF) approach based on terrain constraints to obtain the mass flux variations in the southern Tibetan Plateau. From the results of simulated data, compared with the actual signal, the Nash – Sutcliffe efficiency (NSE) calculated using the ISDF method (more than 0.86) is much higher than the traditional filtering result. Compared with the traditional filtering method (i.e. unconstrained Gaussian Filtering), the root mean squared error (RMSE) is reduced by about 27.7% of that calculated using the ISDF method from the simulated data with north-south stripes and noise. Moreover, the signal-to-noise ratio (SNR) calculated using the ISDF method has also been significantly improved. In the GRACE/GRACE-FO SHCs experiments, we compared the results calculated using the ISDF method with the mascon solutions of the three official centres, i.e. Center for Space Research (CSR), Jet Propulsion Laboratory (JPL), and Goddard Space Flight Center (GSFC). The results of time series decomposition show that the signals calculated using the ISDF method agree well with the mean-mascon solution and the annual amplitude and semi-annual amplitude differences between the two data are 0.01 cm and −0.61 cm, respectively. Our results underline that the ISDF is an efficient approach for estimating mass flux variations in the southern Tibetan Plateau from GRACE/GRACE-FO SHCs. Finally, we analysed the mass attenuation rates in three periods and the possible reasons in the southern Tibetan Plateau based on the different hydrological models.

Multiscale oscillations of the annual course of temperature affect the spawning events of rudd (Scardinus erythrophthalmus)

Identifying climate impacts on ecosystems and their components requires observing time series of sufficient length to ensure adequate statistical power and reasonable coverage of the historical range of variability inherent in the system. The complexity of the hierarchy of climate effects reflected in temporal patterns in time series creates a need to be accurately modeled. The life cycle phenomena of living organisms, including fish spawning, have the character of one-time or time-limited events in time. An approach to finding the relationship between continuous components of time dynamics of environment properties and life cycle events of living organisms was proposed. This approach allowed us to evaluate the role of temperature patterns in the phenology of spawning rudd (Scardinus erythrophthalmus Linnaeus, 1758) in the Dnipro River basin water bodies. The atmospheric temperature time series may be decomposed into the following components: trend, annual cycle, episodic component, harmonic component, extreme events, and noise. Systematically low water temperatures at the beginning of the spawning period were observed in the Protoka River system and the Obukhov floodplain, and systematically elevated temperatures were recorded in the Dnipro River. The annual temperature dynamics was shown to be presented as a composition of oscillatory processes of different scale levels. The sinusoidal trend was previously extracted from the temperature series data. The average annual temperature, amplitude, and phase shift were calculated on the basis of the sinusoidal regression model. The residuals of the sinusoidal trend were processed by means of redundancy analysis with variables derived from symmetric distance-based Moran’s eigenvector maps as explanatory predictors. A set of 104 orthogonal dbMEM variables was extracted from the annual time series. These temporal variables were divided into the broad-, medium-, and fine-scale components. The parameters of temperature dynamics and biotope type are able to explain 51–72% of variability of spawning event. The time of spawning in water bodies corresponds to the time of spawning start: the earlier spawning starts, the earlier it ends. The duration of the spawning season is influenced by the patterns of different scale levels, as well as the amplitude and shift of phases. In this case, the duration of spawning in all water bodies does not differ. Spawning temperature depends on medium- and fine-scale temperature patterns, but does not depend on the characteristics of the sinusoidal annual trend. The annual temperature variation has been shown to be such that it can be decomposed into a sinusoidal trend, patterns of a multiscale nature, and a random fraction. Over the time range studied, the trend of increasing mean annual temperature was not statistically significant for spawning events. The sinusoidal trend explains 78.3–87.6% of the temperature variations and depends on the mean annual temperature, the amplitude of temperature variations during the year, and the earlier or later seasons of the year. Amplitude and phase shift play a role in describing spawning phenology. The residuals of the sinusoidal trend have been explained using dbMEM variables. This variation was decomposed into large-scale, medium-scale, and small-scale components. Winter and spring temperature fluctuations prior to spawning initiation had the greatest effect on spawning. Water temperature determines the lower possible limit for the start of spawning, but the actual start of spawning is determined by the preceding temperature dynamics. The results of the study have implications for understanding the dynamics of fish populations and assessing the influence of environmental conditions on the harmonization of the various components of ecosystems.

Excess Heat Factor climatology, trends, and exposure across European Functional Urban Areas

In Europe, regional climate change prospects indicate the urgency of adapting to extreme weather events. While increasing temperature trends have already been detected, in the last decades, the adoption of a European heatwave (HW) early-warning index is not yet consensual, partially due to the significant number of alternative algorithms, in some cases adjusted to the measurement of sector-specific impacts (as per the Expert Team on Climate Risk and Sector-specific Indices (ET-SCI)). In particular, the Excess Heat Factor (EHF) has been shown to accurately predict heat-related human health outcomes, in mid-latitude climates, provided that local summer exposure to excess heat is mostly driven by extreme air temperatures, with a lower contribution from relative humidity. Here, annual summaries of EHF-based HW detection were calculated for the European region, using daily maximum and minimum temperatures from the homogenised version of the E-OBS gridded dataset. Annual HW frequencies, duration, mean magnitude, maximum amplitude, and severity were subject to climatology and trend analysis across the European biogeographical regions, considering the 1961–1990 period as the baseline reference for anomaly detection in the more recent (1991–2018) decades. As HW-dependent morbidity/mortality affects mostly the elderly, an EHF-based HW Exposure Index was also calculated, by multiplying the recent probability of severe events per the number of people aged 65, or more, in the European Functional Urban Areas (FUAs). Results show that recent historical EHF-based patterns diverge across European Biogeographical regions, with a clear latitudinal gradient. Both the historical mean and recent trends point towards the greater exposure in the southern European Mediterranean region, driven by the significant increase of HW frequency, duration and maximum severity, especially in the last 3 decades; conversely, annual maximum EHF intensities (i.e., greatest deviations from the local 90th daily mean temperature) are mostly found in the northern and/or high altitude Boreal, Alpine and Continental regions, as a consequence of the latitudinal effect of local climatology on the HWM/HWA indices (this also translates into greater magnitudes of change, in this regions). Nonetheless, by simultaneously considering the probability of Severe HW occurrence in the last three decades, together with the log transformation of people aged 65 or more, results show that greater HW Exposure Indices affect FUAs across the whole Europe, irrespective of its regional climate, suggesting that more meaningful vulnerability assessments, early warning and adaptation measures should be prioritized accordingly.

A combined use of in situ and satellite-derived observations to characterize surface hydrology and its variability in the Congo River basin

Abstract. The Congo River basin (CRB) is the second largest river system in the world, but its hydroclimatic characteristics remain relatively poorly known. Here, we jointly analyse a large record of in situ and satellite-derived observations, including a long-term time series of surface water height (SWH) from radar altimetry (a total of 2311 virtual stations) and surface water extent (SWE) from a multi-satellite technique, to characterize the CRB surface hydrology and its variability. First, we show that SWH from altimetry multi-missions agrees well with in situ water stage at various locations, with the root mean square deviation varying from 10 cm (with Sentinel-3A) to 75 cm (with European Remote Sensing satellite-2). SWE variability from multi-satellite observations also shows a plausible behaviour over a ∼25-year period when evaluated against in situ observations from the subbasin to basin scale. Both datasets help to better characterize the large spatial and temporal variability in hydrological patterns across the basin, with SWH exhibiting an annual amplitude of more than 5 m in the northern subbasins, while the Congo River main stream and Cuvette Centrale tributaries vary in smaller proportions (1.5 to 4.5 m). Furthermore, SWH and SWE help illustrate the spatial distribution and different timings of the CRB annual flood dynamic and how each subbasin and tributary contribute to the hydrological regime at the outlet of the basin (the Brazzaville/Kinshasa station), including its peculiar bimodal pattern. Across the basin, we estimate the time lag and water travel time to reach the Brazzaville/Kinshasa station to range from 0–1 month in its vicinity in downstream parts of the basin and up to 3 months in remote areas and small tributaries. Northern subbasins and the central Congo region contribute highly to the large peak in December–January, while the southern part of the basin supplies water to both hydrological peaks, in particular to the moderate one in April–May. The results are supported using in situ observations at several locations in the basin. Our results contribute to a better characterization of the hydrological variability in the CRB and represent an unprecedented source of information for hydrological modelling and to study hydrological processes over the region.

Changes in the permafrost environment under dual impacts of climate change and human activities in the Hola basin, northern Da Xing'anling Mountains, Northeast China

AbstractThe Hola basin in the northern Da Xing'anling Mountains in Northeast China has been extensively developed for coal mining since the 1980s, resulting in a significantly degrading permafrost environment. However, the changing thermal state of permafrost under the boreal forest remains unclear. Based on ground temperature records from nine monitoring boreholes at three areas (disturbed, backfilled, and undisturbed areas) from 2015 to 2020, the thermal state of permafrost under the dual influences of climate change and human activities were evaluated. It is found that the temperatures at the depth of zero annual amplitude (TZAA) in the disturbed area increased by 0.2–0.5°C during the past 6 years, turning the cold permafrost (TZAA ≤ −1.0°C) into a warm one (−1 ≤ TZAA ≤ 0°C). Additionally, the permafrost table was lowered by 0.8–7.0 m. As a result, subaerial supra‐permafrost talik occurred. However, TZAA in the undisturbed areas lowered by 0.03–0.11°C, possibly due to the lagged response of the local climate cooling during 2001–2010. In the meantime, TZAA rose sharply in the disturbed areas, indicating more significant influences of intense human activities on permafrost in comparison with that of climate change. As the permafrost degrades, the boreal permafrost eco‐environment has changed dramatically, as revealed by the draining and drying up of the Yueya'hu Lake in the southern Hola basin. These results help reveal the physical mechanisms, evaluate the rates and amplitudes of environmental changes, and manage the boreal forest environment and resources in a sustainable manner.

Hydroacoustics and concurrent experimental trawling reveal extreme annual variation in the density of 0+ pikeperch in late summer

The density and mean size of 0 + pikeperch (Sander lucioperca) were studied in late summer in 2004–2017 in clay-turbid and eutrophic Lake Tuusulanjärvi in southern Finland. Hydroacoustics and simultaneous experimental trawling were used to estimate the density of 0 + pikeperch. In some autumns, 0 + pikeperch was the most abundant species in the pelagic fish assemblage. However, the annual amplitude of pikeperch density was extremely high (1,300 - 19,900 individuals ha−1). The density and size variations of 0 + pikeperch were analysed in relation to air temperature sums and degree days. Unexpectedly, the density of 0 + pikeperch showed no correlation with the air temperature sums or degree days, but both the mean length and weight of 0 + pikeperch correlated positively with these temperature variables. The highest correlation coefficients between mean size and temperature were found with temperature sums over 10 °C and degree days over 5 °C. The correlation between density and condition of 0 + pikeperch was negative but non-significant. The high density of 0 + pikeperch in some autumns suggests that pikeperch may play a central role in the pelagic food web in eutrophic lakes – not only as a predator of planktivores but also by its own planktivory.

Atomic Oxygen SAO, AO and QBO in the Mesosphere and Lower Thermosphere Based on Measurements from SABER on TIMED during 2002–2019

Using version 1.0 of TIMED/SABER nighttime O(3P) density data in the mesosphere and lower thermosphere (MLT) retrieved from 2.0 and 1.6 μm radiances, we conducted a study on the semiannual oscillation (SAO), annual oscillation (AO) and quasi-biennial oscillation (QBO) of the atomic oxygen volume mixing ratio at 96 km, from 40° S to 40° N, for 2002–2019. We first analyzed the altitude profiles of the atomic oxygen volume mixing ratio and kinetic temperature, and chose to study the daily average of the atomic oxygen volume mixing ratio at 96 km. For the analysis of SAO and AO, we fitted two sinusoidal functions with periods of 6 and 12 months to the daily mean atomic oxygen volume mixing ratio to obtain the annual and semiannual amplitude. The SAO amplitudes had two peaks of 1.68 × 10−3 and 1.63 × 10-3 at about 25° S and 25° N, and displayed a clear hemispheric symmetry. The AO amplitude increased with the latitude and showed distinct minima (valleys) of 3.36 × 10−4 around the equator, as well as a clear hemispheric asymmetry. The correlation coefficient between the atomic oxygen volume mixing ratio QBO with equatorial stratospheric QBO was higher in the tropics than the mid latitudes.

Spatial and Temporal Variability of Permafrost in the Western Part of the Russian Arctic

Climate warming in the Russian Arctic over the past 40 years shows a variety of patterns at different locations and time periods. In the second half of the 20th century, the maximum rates of warming were characteristic of the subarctic permafrost regions of Russia. But in the 21st century, the locations of the greatest rates of climate warming moved to the Arctic zone of Russia. It was one of the reasons for a sharp increase in permafrost temperatures, an increase in the depth of seasonal thaw, and the formation of closed taliks. It was found that as a result of climate change, the differences in permafrost temperatures between different cryogenic landscapes in the area of continuous and discontinuous permafrost distribution have decreased, and in the area of sporadic permafrost distribution are now practically absent. The thermal regime of the ground shows dramatic changes everywhere with a pronounced reduction in the depth of zero annual amplitude.

Tracking the source direction of surface mass loads using vertical and horizontal displacements from satellite geodesy: A case study of the inter-annual fluctuations in the water level in the Great Lakes

Climate oscillations with seasonal and longer periods drive surface water cycles and quasi-cycles at regional and global scales. Changes in terrestrial water storage produce responses in the Earth's gravitational field and crustal deformation. Here, we use techniques from the Global Positioning System (GPS) and the Gravity Recovery and Climate Experiment (GRACE) to reveal a normal pattern of inter-annual fluctuations in the water level in the North American Great Lakes (GL). The GRACE-estimated time series was in good agreement with in situ water level measurements from 2002 to 2018, especially in terms of phases. The amplitude of 3–4 inter-annual signals in water thickness was 4–6 cm, which is equivalent to a 50–75 km3 oscillation in surface water volume within the entire GL. The slightly larger annual and inter-annual fluctuation amplitudes estimated using GRACE data indicate that the aquifer system of the GL and its surroundings also contributes to seasonal mass changes. After 2013, water levels in the GL region rose abruptly, and the water mass increased by nearly 270 km3 until the end of 2018. We also used GPS- and GRACE-derived three-component displacements (vertical, northward, and eastward) to identify load patterns. GPS- and GRACE-estimated maximum probability source directions based on multi-channel singular spectrum analysis showed that most of the selected GPS sites point to the GL region, although the direction deviations of GPS results at a few sites are mainly caused by the combined effect of the local load and superposition of the distant GL. Our findings indicate that inter-annual displacement changes at different frequencies (1- to 8-year cycle) are primarily due to water volume fluctuations in the GL. The amplitudes estimated by GPS are greater than the GRACE-based and GL-modeled results at most stations, which reflects sensitivity differences between these geodetic solutions to the surface load, as hydrological processes in the local area around a station are difficult to identify using GRACE data with a resolution of ~300 km.

Temperature field spatio-temporal law and frozen-depth calculation of a tunnel in a seasonally frozen region

The freezing-thawing process in seasonally frozen regions may cause damage to underground structures, especially tunnels. The temperature field and frozen depth can provide reference for tunnel frost damage treatment. Based on the Banshiling tunnel in Northeast China, the spatio-temporal distribution of the tunnel temperature field was revealed using a self-designed intelligent monitoring system. Combined with the temperature field characteristics, a modified formula for predicting frozen depth was established considering the unfrozen water content. Also, the rationality of the modified formula was verified using an example. The calculation error of the modified formula is 1.23% to 15.63%, which is highly consistent with the observed value. Comparing the spatio-temporal distribution of temperature field and frozen depth, they have high consistency. And both them are approximately symmetrically distributed along the longitudinal direction of the tunnel: the lower the temperature, the greater the frozen depth, and the smaller the longitudinal variation along the tunnel. The sensitivity of frozen depth to geographical factors and parameter factors was explored to clarify the influence of different factors on frozen depth. The results show that the sensitivity of the frozen depth to latitude is much greater than that to altitude, and the sensitivity of the frozen depth to different calculation parameters is in the order of mean annual temperature, initial ground temperature, water content, annual temperature amplitude, and thermal conductivity.

The Crustal Vertical Deformation Driven by Terrestrial Water Load from 2010 to 2014 in Shaanxi–Gansu–Ningxia Region Based on GRACE and GNSS

The terrestrial water resources in Shaanxi–Gansu–Ningxia (SGN) region are relatively scarce, and its climate change is unstable. Research on the deformation driven by terrestrial water load is of great significance to the dynamic maintenance of reference station networks. In this paper, data derived from Gravity Recovery and Climate Experiment (GRACE) and Global Navigation Satellite System (GNSS) from 2010 to 2014 were combined to monitor the spatiotemporal characteristics of surface vertical deformation caused by terrestrial water load change. The single scale factor was calculated by comparing CPC, WGHM, and GLDAS hydrological model to restore filtering leakage signal. The singular spectrum analysis (SSA) method was used to extract the principal component of temporal vertical deformation, and its spatial distribution was analyzed. At the same time, in order to study the relationship between the terrestrial water load deformation from GRACE and that from GNSS, the first-order term correction, the Atmosphere and Ocean De-aliasing Level-1B product (GAC) correction, and the first-order load LOVE number correction for GRACE were adopted in this paper. In addition, a quantitative comparative analysis of both the monitoring results was carried out. The results show that the time-variable characteristics of surface vertical deformation characterized by the filtered three hydrological models were consistent with those of GRACE. The correlation coefficient and Nash–Sutcliffe efficiency coefficient (NSE) values were the highest in the GLDAS model and the GRACE model, respectively; the former index is 0.93, while the latter is 0.85. The crustal vertical deformation from terrestrial water load showed a declining rate from 2010 to 2014. Its spatial change rate showed an obvious ladder distribution, with the surface subsidence rate gradually decreasing from south to north. In addition, weighted root mean square (WRMS) contribution rate of the crustal vertical deformation resulting from GRACE with GAC correction between the different GNSS stations ranged from 18.52% to 54.82%. The correlation coefficient between them was close to 0.70. After deducting the mass load impact of GRACE only, the WRMS contribution rate of the corresponding stations decreased from −8.42% to 21.18%. The correlation coefficient between them reduced noticeably. Adding GAC back can increase the comparability with GRACE and GNSS in terms of monitoring the crustal vertical deformation. The annual amplitude and phase of surface vertical deformation resulting from GRACE with GAC correction were close to those of GNSS. The research results can help to explore the motion mechanism between water migration and surface deformation, which is of benefit in the protection of the water ecological environment in the region.

Application of independent component analysis to GPS position time series in Yunnan Province, southwest of China

Pervasive seasonal signals have been found in GPS site position time series. A critical aspect in the seasonal geodetic analysis is the identification and extraction of different sources of deformations in space and time domains. In this work, we applied the independent component analysis (ICA) to discriminate four different seasonal periods in GPS time series: spatial uniformly distributed annual signals, local annual variations with spatial heterogeneity, spurious signals of draconitic terms, and semiannual terms. The annual displacements could be well described by surface mass loadings. As we successfully identified the draconitic terms, we removed these terms from the GPS time series and re-estimated the annual signals from the GPS; the annual amplitude reduced by ∼1 mm on average. Our results show that the GPS draconitic terms bias the annual signal estimation in conventional sinusoidal model fitting and that the ICA can be successfully used to extract different seasonal periods. We recommend removing the draconitic terms before estimating the annual signals, which are intended for high-accuracy applications.

Tidal energy potential in coastal Vietnam

Tidal energy is a renewable energy source produced by the rise and fall of ocean tides. Tidal energy can be exploited using a special type of generator that converts tidal energy into electricity. Tidal power generation has the potential to open up many prospects for energy field and minimize carbon dioxide emissions that cause the greenhouse effect. To evaluate the possibility of tidal power, it is necessary to have documents and data on average annual tidal amplitude, tidal regime, and main tidal waves in the study area. To calculate the tidal power potential for the east coast of Vietnam, this article applies the calculation formula of tidal power energy by Russian scientist L.B. Bernstein. The annual mean tidal amplitude and the K1, O1, and M2 wave amplitude data at nearly 2000 calculation points along the coast of Vietnam were extracted from the TPOX8-Atlas harmonic constant set. Research results showed that Vietnam has great potential for tidal energy along the Hai Phong - Quang Ninh coastal area and the southeast region with a prospective 41.6 GWh/km2/y.

Climate-inferred distribution estimates of mid-to-late Pliocene hominins

During the mid-to-late Pliocene (ca. 4–3 Ma), several hominin species were present in central Sahel, eastern and southern Africa. The potential for the discovery of hominin remains from this interval is limited by the availability of exposed Pliocene deposits and the ability to investigate them. As a result, most discoveries have been made in the Afar region of Ethiopia and in the Lake Turkana basin, thus unveiling only a portion of Pliocene hominins' probable geographical presence. In this study we provide a continental view of geographic areas potentially accessible to these hominins. To do so, we estimate the climatic envelope suitable for mid-to-late Pliocene hominin presence, using the earth system model IPSL-CM5A and the Maxent habitat suitability algorithm. Our analysis reveals high habitat suitability for these hominin species in semi-arid regions where annual thermal amplitude and mean annual precipitation are moderate, mostly corresponding to tropical xerophytic shrublands. Our habitat model estimates geographically continuous, suitable climatic conditions for hominins between central Sahel and northeastern Africa, but not between eastern and southern Africa. This discontinuity suggests that southern African and eastern African hominins were separated by an environmental barrier that could only be crossed during particularly favourable periods or by undertaking long-range dispersal over climatically hostile habitats. Under climate conditions of northern hemisphere summer at perihelion this climatic barrier is not present. In contrast, the Turkana basin, the Laetoli region, and a large part of southern Africa remain suitable for all precession angles, suggesting that these areas may have functioned as refugia. The constant presence of these stable areas combined with the periodic establishment of corridors for dispersion can potentially explain hominin diversity in eastern Africa. • Paleoclimatic reconstructions and HSM depict high suitability in semi-arid regions • Eastern and southern suitable areas are disconnected under mean Pliocene climate • Under specific precession configurations this climatic barrier disappears • Turkana basin and the Laetoli region could have work as climatic refugia • High Pliocene Hominin diversity could be linked with periodic presence of corridors.

New high-resolution estimates of the permafrost thermal state and hydrothermal conditions over the Northern Hemisphere

Abstract. Monitoring the thermal state of permafrost (TSP) is important in many environmental science and engineering applications. However, such data are generally unavailable, mainly due to the lack of ground observations and the uncertainty of traditional physical models. This study produces novel permafrost datasets for the Northern Hemisphere (NH), including predictions of the mean annual ground temperature (MAGT) at the depth of zero annual amplitude (DZAA) (approximately 3 to 25 m) and active layer thickness (ALT) with 1 km resolution for the period of 2000–2016, as well as estimates of the probability of permafrost occurrence and permafrost zonation based on hydrothermal conditions. These datasets integrate unprecedentedly large amounts of field data (1002 boreholes for MAGT and 452 sites for ALT) and multisource geospatial data, especially remote sensing data, using statistical learning modeling with an ensemble strategy. Thus, the resulting data are more accurate than those of previous circumpolar maps (bias = 0.02±0.16 ∘C and RMSE = 1.32±0.13 ∘C for MAGT; bias = 2.71±16.46 cm and RMSE = 86.93±19.61 cm for ALT). The datasets suggest that the areal extent of permafrost (MAGT ≤0 ∘C) in the NH, excluding glaciers and lakes, is approximately 14.77 (13.60–18.97) × 106 km2 and that the areal extent of permafrost regions (permafrost probability >0) is approximately 19.82×106 km2. The areal fractions of humid, semiarid/subhumid, and arid permafrost regions are 51.56 %, 45.07 %, and 3.37 %, respectively. The areal fractions of cold (≤-3.0 ∘C), cool (−3.0 ∘C to −1.5 ∘C), and warm (>-1.5 ∘C) permafrost regions are 37.80 %, 14.30 %, and 47.90 %, respectively. These new datasets based on the most comprehensive field data to date contribute to an updated understanding of the thermal state and zonation of permafrost in the NH. The datasets are potentially useful for various fields, such as climatology, hydrology, ecology, agriculture, public health, and engineering planning. All of the datasets are published through the National Tibetan Plateau Data Center (TPDC), and the link is https://doi.org/10.11888/Geocry.tpdc.271190 (Ran et al., 2021a).

Assessment of GRACE/GRACE Follow-On Terrestrial Water Storage Estimates Using an Improved Forward Modeling Method: A Case Study in Africa

Leakage errors derived from spatial filters are the major limitation for estimating terrestrial water storage via the Gravity Recovery and Climate Experiment (GRACE) mission and the recently launched GRACE Follow-On mission. Here we develop an improved forward modeling method and assess its performance of reducing leakage errors over Africa. In noise-free condition, the forward modeling method shows its outperformance in restoring signals, and the improved forward modeling method can further reduce the leakage errors along the coastline of Africa. In noise-contaminated condition, the simulated environment is set as real as possible to GRACE mission and GRACE Follow-On mission. The results based on the simulated GRACE and GRACE Follow-On solutions demonstrate the capacity of improved forward modeling method in reducing leakage errors. In the case of simulated GRACE data, the average improvements of 24 basins over Africa are respectively 37% for annual amplitudes and 36% for trends. When compared with these simulated GRACE data, the improvements via simulated GRACE Follow-On solutions are minor over large and medium size river basins, but they are significant over small size river basins. In the case of simulated GRACE Follow-On solutions, the average improvements over Africa are 39% for annual amplitudes and 41% for trends. Eventually, the improved forward modeling method is used to process GRACE spherical harmonic datasets from the Center for Space Research (CSR). The results present better agreement with those derived from the newly released mascon solutions from Jet Propulsion Laboratory (JPL) and CSR, when compared with those derived from CSR Tellus grids with scale factors. The better consistency between these model-independent approaches indicates the good performance of our improved forward modeling method and the further necessity of careful evaluation of model-dependent approaches when using different prior hydrological models. Overall, experiments based on noise-free observations, noise-contaminated observations, and GRACE datasets indicate that improved forward modeling method is capable of restoring temporal signals.

Thermal conductivity contrast effect of organic soils and its environmental implications

Thermal conduction control is important for retarding permafrost degradation and mitigating of frost geohazards. Similar to a thermodiode, high thermal conductivity contrast (HTCC) materials can serve as good thermal insulators. A preferred HTCC material for ground cooling is larger in thermal resistance in summer and smaller in winter. Because of contrasting thermal conductivity under frozen and thawed states, organic soil is blessed with such a property. This study quantified and reported the HTCC effects on a range of soil organic matter concentrations (SOMC) and soil moisture saturation degree (SMSD). Using the COMSOL, influences of different SOMC and SMSD on ground temperatures were simulated and compared with laboratory-measured properties. Simulation results demonstrated that with constant SMSD at 20% throughout the year, the thermal insulation effect was strengthened with increasing SOMC. A better insulating effect was judged by lower annual amplitudes and smaller depths of zero annual amplitude of ground temperatures. In case of low SMSD in summer (20%) and high SMSD in winter (60–80%), the HTCC effect of soil is enhanced with increasing SOMC. This enhancement was evidenced by increased thermal offsets and decreased maximum summer and average near-surface soil temperatures. With constant SOMC and increasing SMSD, the rising HTCC effect gradually cools the ground. An integral analysis indicates that the higher the SOMC and SMSD in winter, the larger the thermal offset and the lower the ground temperature, i.e., the greater the HTCC effect of organic soil. This study may provide geocryological bases for engineering and environmental applications in cold regions.

Incidence, circulation, and spatiotemporal analysis of seasonal influenza in Shandong, China, 2008-2019: A retrospective study.

BackgroundUnderstanding the influenza‐like illness (ILI) incidence, circulation pattern of virus strains and spatiotemporal pattern of influenza transmission are important for designing control interventions. Based on the 10 years' surveillance data, we aimed to provide a baseline characterization and the epidemiology and dynamics of influenza virus in Shandong.MethodsWe extracted surveillance and laboratory testing data. We estimated the ILI incidence and analyzed the predominant virus. A wavelet power analysis was used to illustrate the periodicity. In addition, we applied a linear regression model to characterize the correlation of influenza seasonality with longitude.ResultsThe average ILI incidence was estimated to be 3744.79 per 1 million (95% confidence interval [CI]: 2558.09–4931.45) during 2009–2018. Influenza A/H1N1 and A/H3N2 strains predominated in the most influenza seasons in Shandong. The annual amplitude of influenza epidemics decreased with longitude (P < 0.05). In contrast, the epidemic peak of influenza emerged earlier in the western region and increased with longitude in influenza A (P < 0.05). The annual peak of the influenza B epidemic lagged a median of 4.2 weeks compared with that of influenza A.ConclusionsThe development or modification of seasonal influenza vaccination strategies requires the recognition that the incidence is higher in preschool‐ and school‐aged children. Although seasonal influenza circulates annually in Shandong, the predominant virus strain circulation pattern is extremely unpredictable and strengthening surveillance for the predominant virus strain is necessary. Lower longitude inland regions need to take nonpharmaceutical or pharmaceutical interventions in advance during influenza high‐occurrence seasons.

New permafrost is forming on the exposed bottom of Zonag Lake on the Qinghai-Tibet Plateau

Most lakes on the Qinghai-Tibet Plateau have expanded in recent years. Zonag Lake, a critical habitat for Tibetan antelopes in the continuous permafrost zone, burst and overflowed after several years of expansion, resulting in a reduction of approximately 100 km2 in the lake area. Observations have revealed new permafrost is forming on the exposed bottom, accompanied by various periglacial landscapes. The permafrost aggradation on the exposed bottom is rapid, and the permafrost base reached 4.9 m, 5.4 m, and 5.7 m in the first three years, respectively. In this study, the future changes and influencing factors of recently formed permafrost are simulated using a one-dimensional finite element model of heat flow. The simulated results indicate that the permafrost on the exposed bottom is likely to continue to develop, appearing first quick back slow trend. Besides the surface temperature, the annual amplitude is also an important factor in affecting the aggradation of permafrost. The unidirectional permafrost aggradation in the study area is different from the bidirectional permafrost aggradation on the closed taliks around the Arctic. Additionally, snow cover and vegetation are two important factors influencing the future development of permafrost on the exposed lake bottom.