scholarly journals Long-Term Patterns and Trends of Shortwave Global Irradiance over the Euro-Mediterranean Region

Atmosphere ◽  
2021 ◽  
Vol 12 (11) ◽  
pp. 1431
Author(s):  
Elissavet Galanaki ◽  
George Emmanouil ◽  
Konstantinos Lagouvardos ◽  
Vassiliki Kotroni
Keyword(s):  
Mediterranean Region ◽  
Spatiotemporal Variability ◽  
Reanalysis Dataset ◽  
Global Irradiance ◽  
Seasonal Basis ◽  
Region 10 ◽  
Annual Scale ◽  
Good Agreement

The spatiotemporal patterns and trends of shortwave global irradiance (SWGI) are a crucial factor affecting not only the climate but also sectors of the economy. In this work, the ERA5-Land reanalysis dataset is employed and evaluated against in situ measurements from a dense network of surface stations operated by the National Observatory of Athens over Greece, revealing a good agreement between the two datasets. Then, the spatiotemporal variability of SWGI is investigated over the Euro-Mediterranean region (10° W–42° E and 30° N–52° N) for a 40-year period (1981–2020). SWGI exhibits a smooth latitudinal variability from north to south of −5.4 W/m2/degree on an annual scale, while it varies significantly on a seasonal basis and is almost four times lower in the winter than in the summer. The SWGI trend during the analyzed period was found to be positive and statistically significant at the 95% confidence level. Spring and summer are the periods where positive and the strongest rates of SWGI trends are evident, while in the winter and autumn, negative or neutral trends were found. The increasing SWGI trend shows a slowdown during the beginning of the 2000s in all seasons, except autumn. The SWGI trend decreases by about −0.06 W/m2/decade every 100 m of elevation increase.

scholarly journals Favorable climatic regime for maintaining the present-day geometry of the Gregoriev Glacier, Inner Tien Shan

2011 ◽  
Vol 5 (3) ◽  
pp. 539-549 ◽  
Author(s):  
K. Fujita ◽  
N. Takeuchi ◽  
S. A. Nikitin ◽  
A. B. Surazakov ◽  
S. Okamoto ◽  
...  
Keyword(s):  
Mass Balance ◽  
Meteorological Data ◽  
Tien Shan ◽  
Balance Model ◽  
Glacier Mass Balance ◽  
Current State ◽  
Climatic Regime ◽  
Good Agreement

Abstract. We conducted 2 yr (2005–2007) of in situ meteorological and glaciological observations on the Gregoriev Glacier, a flat-top glacier within the Inner Tien Shan, Kyrgyzstan. Relative carrier-phase GPS surveys reveal a vertical lowering at the summit of the glacier. Based on snow density data and an energy-mass balance model, we estimate that the annual precipitation and summer mean temperature required to maintain the glacier in the current state are 289 mm and −3.8 °C at the glacier summit (4600 m a.s.l.), respectively. The good agreement between dynamically derived precipitation and the long-term observed precipitation at a nearby station in the Tien Shan (296 mm at 3614 m a.s.l. for the period 1930–2002) suggests that the glacier has been in a near steady-state in terms of mass supply. The glacier mass-balance, reconstructed based on meteorological data from the Tien Shan station for the past 80 yr, explains the observed fluctuations in glacier extent, particularly the negative mass balance in the 1990s.

scholarly journals Ideal climatic variables for the present-day geometry of the Gregoriev Glacier, Inner Tien Shan, Kyrgyzstan, derived from GPS data and energy-mass balance measurements

2011 ◽  
Vol 5 (2) ◽  
pp. 855-883
Author(s):  
K. Fujita ◽  
N. Takeuchi ◽  
S. A. Nikitin ◽  
A. B. Surazakov ◽  
S. Okamoto ◽  
...  
Keyword(s):  
Mass Balance ◽  
Meteorological Data ◽  
Vertical Surface ◽  
Tien Shan ◽  
Balance Model ◽  
Glacier Mass Balance ◽  
Differential Gps ◽  
Good Agreement

Abstract. We conducted 2 yr (2005–2007) of in situ meteorological and glaciological observations on the Gregoriev Glacier, a flat-top glacier within the Inner Tien Shan, Kyrgyzstan. Differential GPS surveys reveal a vertical surface deletion at the summit of the glacier. Based on snow density data and an energy-mass balance model, we estimate that the annual precipitation and summer mean temperature required to maintain the glacier in the modern state are 289 mm and −3.85 °C at the glacier summit (4600 m above sea level, a.s.l.), respectively. The good agreement between the long-term estimated and observed precipitation at a nearby station in the Tien Shan (292 mm at 3614 m a.s.l. for the period 1930–2002) suggests that the glacier dynamics have been regulated by the long-term average accumulation. The glacier mass-balance, reconstructed based on meteorological data from the Tien Shan station for the past 80 yr, explains the observed fluctuations in glacier extent, particularly the negative mass balance in the 1990s.

Global validation of the ESA CCI+SSS products

2020 ◽  
Author(s):  
Adrien Martin ◽  
Sébastien Guimbard ◽  
Jacqueline Boutin ◽  
Nicolas Reul ◽  
Rafael Catany
Keyword(s):  
Soil Moisture ◽  
European Space Agency ◽  
Ground Truth ◽  
Sea Surface Salinity ◽  
Global Ocean ◽  
Surface Salinity ◽  
Spatial Gradients ◽  
Good Agreement

<p>The European Space Agency (ESA) Climate Change Initiative for Sea Surface Salinity (CCI+SSS) project aims at generating long-term, improved, calibrated global SSS fields from space. The project started in mid-2018 and in its first year has produced a 9-year dataset (2010-2018) from the three available L-band radiometer satellites (SMOS: Soil Moisture and Ocean Salinity; Aquarius; SMAP: Soil Moisture Active Passive) and validated it against in situ references (Argo and ISAS: In Situ Analysis System). The dataset is available at https://catalogue.ceda.ac.uk/uuid/9ef0ebf847564c2eabe62cac4899ec41.</p><p>The comparisons with in situ ground truth indicate much better performances than the ones obtained with a single satellite data product, with global precision against in situ references of 0.16 pss and 0.10 pss in areas with low variability. There is a very good agreement between the CCI dataset and references, including long-term stability, with differences within +-0.05 pss for global ocean within [40°S-20°N]. At higher latitude, we observe seasonal oscillation of the CCI SSS difference against references. The CCI SSS products uncertainty have been validated against references and show good agreement as long as the spatial representativeness is considered in presence of strong spatial gradients in salinity.</p>

Atmospheric Carbon Dioxide and Methane measurements at Sodankylä, Finland

2020 ◽  
Author(s):  
Rigel Kivi ◽  
Huilin Chen ◽  
Juha Hatakka ◽  
Pauli Heikkinen ◽  
Tuomas Laurila ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Atmospheric Carbon Dioxide ◽  
Near Infrared ◽  
Relative Difference ◽  
Total Carbon ◽  
Finnish Meteorological Institute ◽  
Infrared Spectral ◽  
Good Agreement

<p>Carbon dioxide and methane column measurement at the Finnish Meteorological Institute’s Sodankylä facility in northern Finland started in early 2009. The measurements have been taken by a Fourier Transform Spectrometer (FTS) in the near-infrared spectral region. From the spectra column-averaged abundances of CO<sub>2</sub>, CH<sub>4</sub> and other gases are derived. The instrument participates in the Total Carbon Column Observing Network (TCCON).  Here we present long-term ground based FTS measurements of carbon dioxide and methane and comparisons with satellite borne observations. We find that CO<sub>2</sub> column amounts have increased by 2.2 ± 0.1 ppm/year since the start of the measurements in 2009 and CH<sub>4</sub> column amounts have increased by 7 ± 0.4 ppb/year. The measurements are in good agreement with multi-year measurements by the Greenhouse Gases Observing Satellite (GOSAT): the relative difference in XCH<sub>4</sub> has been -0.07 ± 0.02 % and the relative difference in XCO<sub>2</sub> has been 0.04 ± 0.02 %. Finally we use balloon borne AirCore observations at the Sodankylä site to provide comparisons between FTS and in situ observations during all seasons.</p>

scholarly journals The East Madagascar Current: Volume Transport and Variability Based on Long-Term Observations

2016 ◽  
Vol 46 (4) ◽  
pp. 1045-1065 ◽  
Author(s):  
Leandro Ponsoni ◽  
Borja Aguiar-González ◽  
Herman Ridderinkhof ◽  
Leo R. M. Maas
Keyword(s):  
Volume Transport ◽  
Altimeter Data ◽  
Surface Transport ◽  
Sea Level Anomalies ◽  
Anticyclonic Eddies ◽  
Satellite Altimeter Data ◽  
Observational Program ◽  
Good Agreement

AbstractThis study provides a long-term description of the poleward East Madagascar Current (EMC) in terms of its observed velocities, estimated volume transport, and variability based on both ~2.5 yr of continuous in situ measurements and ~21 yr of satellite altimeter data. An array of five moorings was deployed at 23°S off eastern Madagascar as part of the Indian–Atlantic Exchange in present and past climate (INATEX) observational program. On average, the EMC has a horizontal scale of about 60–100 km and is found from the surface to about 1000-m depth. Its time-averaged core is positioned at the surface, at approximately 20 km from the coast, with velocity of 79 (±21) cm s−1. The EMC mean volume transport is estimated to be 18.3 (±8.4) Sverdrups (Sv; 1 Sv ≡ 106 m3 s−1). During the strongest events, maximum velocities and transport reach up to 170 cm s−1 and 50 Sv, respectively. A good agreement is found between the in situ transport estimated over the first 8 m of water column [0.32 (±0.13) Sv] with the altimetry-derived volume transport [0.28 (±0.09) Sv]. Results from wavelet analysis display a dominant nearly bimonthly (45–85 days) frequency band of transport variability, which explains about 41% of the transport variance. Altimeter data suggest that this band of variability is induced by the arrival of westward-propagating sea level anomalies, which in turn are likely represented by mesoscale cyclonic and anticyclonic eddies. Annual averages of the altimeter-derived surface transport suggest that interannual variabilities also play a role in the EMC system.

scholarly journals Multi-model simulation of CO and HCHO in the Southern Hemisphere: biogenic emissions and model uncertainties

2015 ◽  
Vol 15 (2) ◽  
pp. 2615-2678 ◽  
Author(s):  
G. Zeng ◽  
J. E. Williams ◽  
J. A. Fisher ◽  
L. K. Emmons ◽  
N. B. Jones ◽  
...  
Keyword(s):  
Southern Hemisphere ◽  
Atmospheric Chemistry ◽  
Model Simulation ◽  
Biogenic Emissions ◽  
Biogenic Emission ◽  
Source Regions ◽  
The Impact ◽  
Good Agreement

Abstract. We investigate the impact of biogenic emissions on carbon monoxide (CO) and formaldehyde (HCHO) in the Southern Hemisphere (SH), with simulations using two different biogenic emission inventories for isoprene and monoterpenes. Results from four atmospheric chemistry models are compared to continous long-term ground-based CO and HCHO column measurements at SH NDACC sites, and to in situ surface CO measurements from across the SH, representing a subset of the NOAA GMD network. Simulated mean model CO using the CLM-MEGANv2.1 inventory is in good agreement with both column and surface observations, whereas simulations adopting LPJ-GUESS emissions markedly underestimate measured column and surface CO at most sites. Differences in biogenic emissions cause large differences in CO in the source regions which propagate to the remote SH. Significant inter-model differences exist in modelled column and surface CO, due mainly to differences in the models' oxidation schemes for volatile organic compounds; secondary production of CO dominates these inter-model differences. While biogenic emissions are a significant factor in modelling SH CO, inter-model differences pose an additional challenge to constrain these emissions. Corresponding comparisons of HCHO columns at two SH mid-latitude sites reveal that all models significantly underestimate the observed values by approximately a factor of 2. There is a much smaller impact on HCHO of the significantly different biogenic emissions in remote regions, compared to the source regions. Decreased biogenic emissions cause decreased CO export to remote regions, which leads to increased OH; this in turn results in increased HCHO production through methane oxidation. In agreement with earlier studies, we corroborate that significant HCHO sources are likely missing in the models in the remote SH.

scholarly journals Mechanism of the Sleeper-Ballast Dynamic Impact in Void Zones

2021 ◽  
Author(s):  
Mykola Sysyn ◽  
Michal Przybylowicz ◽  
Olga Nabochenko ◽  
Jianxing Liu
Keyword(s):  
Rolling Stock ◽  
Impact Point ◽  
Dynamic Impact ◽  
Quasistatic Loading ◽  
The Impact ◽  
Intensive Development ◽  
Specific Impact ◽  
Good Agreement

Unsupported sleepers or void zones in ballasted tracks are one of the most recent and frequent track failures. The void failures have the property of intensive development that, without timely maintenance measures, can cause the appearance of cost-expensive local instabilities like subgrade damages. The reason of the intensive void development lies in the mechanics of the sleeper and ballast bed interaction. The particularity of the interaction is a dynamic impact that occur due to void closure. Additionally, void zones cause inhomogeneous ballast pressure distribution between the void zone and fully supported neighbour zones. The present paper is devoted studying the mechanism of the sleeper-ballast dynamic impact in the void zone. The results of experimental in-situ measurements of rail deflections showed the significant impact accelerations in the zone even for light-weight slow vehicles. A simple 3-beam numerical model of track and rolling stock interaction has shown the similar to the experimental measurements dynamic interaction. Moreover, the model shows that the sleeper accelerations are more than 3 times higher than the corresponding wheel accelerations and the impact point appear before the wheel enters the impact point. The analysis of ballast loadings shows the specific impact behaviour in combination with the quasistatic part that is different for void and neighbour zones, which are characterised with high ballast pre-stressed conditions. The analysis of void sizes influence demonstrate that the impact loadings, wheel and sleeper maximal accelerations appear at certain void depth after which the values decrease. The ballast quasistatic loading analysis indicates more than twice increase of the ballast loading in neighbour zones for long voids and almost full quasistatic unloading for short length voids. However, the used imitation model cannot explain the nature of the dynamic impact. The mechanism of the void impact is clearly explained by the analytic solution using a simple clamped beam. A simplified analytical expression of the void impact velocity shows that it is linearly related to the wheel speed and loading. The comparison to the numerically simulated impact velocities shows a good agreement and the existence of the void depth with the maximal impact. An estimation of the long-term influences for the cases of normal sleeper loading, high ballast pre-stress and quasistatic loading in the neighbour zones and high impact inside the void are performed.

scholarly journals Temporal evolution of temperatures in the Red Sea and the Gulf of Aden based on in situ observations (1958–2017)

Ocean Science ◽  
2020 ◽  
Vol 16 (1) ◽  
pp. 149-166
Author(s):  
Miguel Agulles ◽  
Gabriel Jordà ◽  
Burt Jones ◽  
Susana Agustí ◽  
Carlos M. Duarte
Keyword(s):  
Red Sea ◽  
Temporal Evolution ◽  
Optimal Interpolation ◽  
Strong Impact ◽  
Gulf Of Aden ◽  
In Situ Observations ◽  
Spatio Temporal ◽  
Good Agreement

Abstract. The Red Sea holds one of the most diverse marine ecosystems in the world, although fragile and vulnerable to ocean warming. Several studies have analysed the spatio-temporal evolution of temperature in the Red Sea using satellite data, thus focusing only on the surface layer and covering the last ∼30 years. To better understand the long-term variability and trends of temperature in the whole water column, we produce a 3-D gridded temperature product (TEMPERSEA) for the period 1958–2017, based on a large number of in situ observations, covering the Red Sea and the Gulf of Aden. After a specific quality control, a mapping algorithm based on optimal interpolation have been applied to homogenize the data. Also, an estimate of the uncertainties of the product has been generated. The calibration of the algorithm and the uncertainty computation has been done through sensitivity experiments based on synthetic data from a realistic numerical simulation. TEMPERSEA has been compared to satellite observations of sea surface temperature for the period 1981–2017, showing good agreement especially in those periods when a reasonable number of observations were available. Also, very good agreement has been found between air temperatures and reconstructed sea temperatures in the upper 100 m for the whole period 1958–2017, enhancing confidence in the quality of the product. The product has been used to characterize the spatio-temporal variability of the temperature field in the Red Sea and the Gulf of Aden at different timescales (seasonal, interannual and multidecadal). Clear differences have been found between the two regions suggesting that the Red Sea variability is mainly driven by air–sea interactions, while in the Gulf of Aden the lateral advection of water plays a relevant role. Regarding long-term evolution, our results show only positive trends above 40 m depth, with maximum trends of 0.045 + 0.016 ∘C decade−1 at 15 m, and the largest negative trends at 125 m (-0.072+0.011 ∘C decade−1). Multidecadal variations have a strong impact on the trend computation and restricting them to the last 30–40 years of data can bias high the trend estimates.

Validation of the ESA CCI+SSS products

2021 ◽  
Author(s):  
Adrien Martin ◽  
Sébastien Guimbard ◽  
Jacqueline Boutin ◽  
Nicolas Reul ◽  
Rafael Catany ◽  
...  
Keyword(s):  
Soil Moisture ◽  
European Space Agency ◽  
Ground Truth ◽  
Sea Surface Salinity ◽  
Global Ocean ◽  
Surface Salinity ◽  
Seasonal Oscillation ◽  
Good Agreement

<div> <p><span>The </span><span>European Space Agency (ESA) Climate Change Initiative (CCI+) for Sea Surface Salinity (CCI+SSS) project aims at generating long-term, improved, calibrated global SSS fields from space. </span>The project started in mid-2018 and in its second year (version 2) has produced a 10-year dataset (2010-2019) from the three available L-band radiometer satellites (SMOS: Soil Moisture and Ocean Salinity; Aquarius; SMAP: Soil Moisture Active Passive) and validated it against in situ references (Argo and ISAS: In Situ Analysis System). The comparisons with in situ ground truth indicate much better performances than the ones obtained with a single satellite data product, with global precision against in situ references of 0.15 pss. CCI SSS version 2 products show similar performance than version 1 but is one year longer. There is a very good agreement between the CCI dataset and references, including long-term stability, with differences within +-0.05 pss for global ocean within [40°S-20°N]. At higher latitude, we observe seasonal oscillation of the CCI SSS difference against references. The uncertainty provided in the CCI SSS product are in good agreement with observations (within +-25%).</p> </div>

scholarly journals Mechanism of Sleeper–Ballast Dynamic Impact and Residual Settlements Accumulation in Zones with Unsupported Sleepers

2021 ◽  
Vol 13 (14) ◽  
pp. 7740
Author(s):  
Mykola Sysyn ◽  
Michal Przybylowicz ◽  
Olga Nabochenko ◽  
Jianxing Liu
Keyword(s):  
Rolling Stock ◽  
Impact Point ◽  
Dynamic Impact ◽  
Quasistatic Loading ◽  
The Impact ◽  
Intensive Development ◽  
Specific Impact ◽  
Good Agreement

Unsupported sleepers or void zones in ballasted tracks are one of the most recent and frequent track failures. The void failures have the property of intensive development that, without timely maintenance measures, can cause the appearance of cost-expensive local instabilities such as subgrade damages. The reason for the intensive void development lies in the mechanics of the sleeper and ballast bed interaction. The particularity of the interaction is a dynamic impact that occurs due to void closure. Additionally, void zones cause inhomogeneous ballast pressure distribution between the void zone and fully supported neighbour zones. The present paper is devoted to studying the mechanism of the sleeper–ballast dynamic impact in the void zone. The results of experimental in situ measurements of rail deflections showed the significant impact accelerations in the zone even for lightweight slow vehicles. A simple three-beam numerical model of track and rolling stock interaction has shown dynamic interaction similar to the experimental measurements. Moreover, the model shows that the sleeper accelerations are more than 3 times higher than the corresponding wheel accelerations and the impact point appears before the wheel enters the impact point. The analysis of ballast loadings shows the specific impact behaviour in combination with the quasistatic part that is different for void and neighbour zones, which are characterised by high ballast pre-stressed conditions. The analysis of void size influence demonstrates that the maximal impact loadings and maximal wheel and sleeper accelerations appear at a certain void depth, after which the values decrease. The ballast quasistatic loading analysis indicates an increase of more than 2 times in the ballast loading in neighbour zones for long voids and almost full quasistatic unloading for short-length voids. However, the used imitation model cannot explain the nature of the dynamic impact. The mechanism of the void impact is clearly explained by the analytic solution using a simple clamped beam. A simplified analytical expression of the void impact velocity shows that it is linearly related to the wheel speed and loading. The comparison to the numerically simulated impact velocities shows a good agreement and the existence of the void depth with the maximal impact. An estimation of the long-term influences for the cases of normal sleeper loading, high ballast pre-stress and quasistatic loading in the neighbour zones and high impact inside the void is performed.

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