scholarly journals Share of Discontinuities in the Ozone Concentration Data from Three Reanalyses

Atmosphere ◽  
2021 ◽  
Vol 12 (11) ◽  
pp. 1508
Author(s):  
Peter Krizan ◽  
Michal Kozubek ◽  
Jan Lastovicka ◽  
Radek Lan
Keyword(s):  
Ozone Concentration ◽  
Temporal Structure ◽  
Reanalysis Data ◽  
Satellite Observations ◽  
The Other ◽  
Trace Gas ◽  
Concentration Data ◽  
Homogeneity Tests ◽  
Spatial Coverage ◽  
Standard Normal

Ozone is a very important trace gas in the stratosphere and, thus, we need to know its time evolution over the globe. However, ground-based measurements are rare, especially in the Southern Hemisphere, and while satellite observations provide broader spatial coverage generally, they are not available everywhere. On the other hand, reanalysis data have regular spatial and temporal structure, which is beneficial for trend analysis, but temporal discontinuities might exist in the data. These discontinuities may influence the results of trend studies. The aim of this paper is to detect discontinuities in ozone data of the following reanalyses: MERRA-2, ERA-5 and JRA-55 with the help of the Pettitt, the Buishand, and the Standard Normal Homogeneity tests above the 500 hPa level. The share of discontinuities varies from 30% to 70% and they are strongly layer dependent. The share of discontinuities is the lowest for JRA-55. Differences between reanalyses were found to be larger than differences between homogeneity tests within one reanalysis. Another aim of this paper is to test the ability of homogeneity tests to detect the discontinuities in 2004 and 2015, when changes in versions of satellite data took place. We showed the discontinuities in 2004 are better detected than those in 2015.

Occurrence of discontinuities in the ozone concentration data from three reanalyses

2020 ◽  
Author(s):  
Peter Krizan ◽  
Michal Kozubek ◽  
Jan Lastovicka
Keyword(s):  
Time Evolution ◽  
Southern Hemisphere ◽  
Ozone Concentration ◽  
Temporal Structure ◽  
The Other ◽  
Trace Gas ◽  
Homogeneity Test ◽  
Concentration Data ◽  
Ozone Data ◽  
Ozone Trend

Abstract. Ozone is a very important trace gas in the stratosphere and thus we need to know its time evolution over the globe. The ground based measurements are rare, especially in the Southern Hemisphere. Satellite ozone data have broader coverage, but they are not available from everywhere. On the other hand, the reanalyse data have regular spatial and temporal structure, which is very good for trend analyses. But there are discontinuities in these data.These discontinuities may influence the result of trend studies. The aim of this paper is to detect the discontinuity occurrence (DO) in the following reanalyses: MERRA-2, ERA-5 and JRA-55 with the help of the Pettitt homogeneity test at all common layers above 500 hPa. The discontinuities are sorted according to their size to the significant and the insignificant ones; the former can affect the ozone trend studies. It was shown that DO for the significant discontinuities is the smallest in JRA-55. In the upper model layers, the discontinuity occurrence is the highest. The other area of high DO is the troposphere.

scholarly journals Modeling of solid sediment transport in mountain rivers

2020 ◽  
Vol 175 ◽  
pp. 12002 ◽  
Author(s):  
Issam Boukhanef ◽  
Anna Khadzhidi ◽  
Lyudmila Kravchenko ◽  
Zeroual Ayoub ◽  
Kastali Abdennour
Keyword(s):  
Sediment Transport ◽  
Fine Particles ◽  
Agricultural Soils ◽  
Suspended Sediments ◽  
High Water ◽  
The Other ◽  
Concentration Data ◽  
Solid Transport ◽  
One Year ◽  
The One

In Algeria, the problems of erosion and sediment transport are critical, since they have the most dramatic consequences of the degradation of agricultural soils on the one hand and the siltation of the dam on the other .The sediment transport in the Algerian basins is very important especially during the periods of floods, It is in this sense that this study, which consists of estimating the sediment transport in suspension and determining the models of relation linking the liquid discharge and the sediment discharge in order to estimate the solid transport in the absence of suspended sediments concentration data at the Sidi Akkacha station at the outlet of the basin of Oued Allala which is subject to a high water erosion, it degrades from one year to the other under the effect of this phenomenon especially during the floods which drain high amounts of fine particles exceeding in general, the concentration of 150 g/l, the results obtained from the application of the models are very encouraging since the correlation between liquid and solid discharge exceeds 80 %.

scholarly journals Structural changes in the shallow and transition branch of the Brewer–Dobson circulation induced by El Niño

2018 ◽  
Author(s):  
Mohamadou Diallo ◽  
Paul Konopka ◽  
Michelle L. Santee ◽  
Rolf Müller ◽  
Mengchu Tao ◽  
...  
Keyword(s):  
El Niño ◽  
Structural Changes ◽  
Lower Stratosphere ◽  
Transport Model ◽  
El Nino ◽  
Southern Oscillation ◽  
Satellite Observations ◽  
Trace Gas ◽  
Residual Circulation ◽  
Mixing Ratios

Abstract. The stratospheric Brewer–Dobson circulation (BD-circulation) determines the transport and lifetime of key radiatively active trace gases and further impacts surface climate through downward coupling. Here, we quantify the variability in the lower stratospheric BD-circulation induced by the El Nino Southern Oscillation (ENSO), using satellite trace gas measurements and simulations with the Lagrangian chemistry transport model, CLaMS, driven by ERA-Interim and JRA-55 reanalyses. We show that despite discrepancies in the deseasonalised ozone (O3) mixing ratios between CLaMS simulations and satellite observations, the patterns of changes in the lower stratospheric O3 anomalies induced by ENSO agree remarkably well over the 2005–2016 period. Particularly during the most recent El Niño in 2015–2016, both satellite observations and CLaMS simulations show the largest negative tropical O3 anomaly in the record. Regression analysis of different metrics of the BD-circulation strength, including mean age of air, vertical velocity, residual circulation and age spectrum, shows clear evidence for structural changes of the BD-circulation in the lower stratosphere induced by El Niño, consistent with observed O3 anomalies. These structural changes during El Niño include a weakening of the transition branch of the BD-circulation between about 370–420 K (∼ 100–70 hPa) and equatorward of about 60° and, a strengthening of the shallow branch at the same latitudes and between about 420–500 K (∼ 70–30 hPa). The strengthening of the shallow branch induces negative tropical O3 anomalies due to enhanced tropical upwelling, while the weakening of the transition branch combined with enhanced downwelling due to the strengthening shallow branch leads to positive O3 anomalies in the extratropical upper troposphere-lower stratosphere (UTLS). Our results suggest that a shift of the ENSO basic state toward more frequent El Niño-like conditions in a warming future climate will substantially alter UTLS trace gas distributions due to these changes in the vertical structure of the stratospheric circulation.

On the Scales Associated with Near-Infrared Reflectance Difference Spectra

1995 ◽  
Vol 49 (6) ◽  
pp. 765-772 ◽  
Author(s):  
M. S. Dhanoa ◽  
S. J. Lister ◽  
R. J. Barnes
Keyword(s):  
Near Infrared ◽  
Scatter Correction ◽  
The Other ◽  
Difference Spectra ◽  
Near Infrared Reflectance ◽  
Standard Normal Variate ◽  
Near Infrared Spectra ◽  
Standard Normal ◽  
Relationship Of ◽  
The Relationship

Scale differences of individual near-infrared spectra are identified when set-independent standard normal variate (SNV) and de-trend (DT) transformations are applied in either SNV followed by DT or DT then SNV order. The relationship of set-dependent multiplicative scatter correction (MSC) to SNV is also referred to. A simple correction factor is proposed to convert derived spectra from one order to the other. It is suggested that the suitable order for the study of changes using difference spectra (when removing baselines) should be DT followed by SNV, which leads to all derived spectra on the scale of mean zero and variance equal to one. If baselines are identical, then SNV scale spectra can be used to calculate differences.

Examining the accuracy of satellite retrievals of trace-gas emissions and lifetimes using high-resolution plume modelling.

2021 ◽  
Author(s):  
Zoe Davis ◽  
Debora Griffin ◽  
Yue Jia ◽  
Susann Tegtmeier ◽  
Mallory Loria ◽  
...  
Keyword(s):  
Wind Direction ◽  
Vertical Profile ◽  
Trace Gases ◽  
Meteorological Conditions ◽  
Point Sources ◽  
Satellite Observations ◽  
Trace Gas ◽  
Vertical Column ◽  
Retrieval Method ◽  
The Impact

<p>A recent method uses satellite measurements to estimate lifetimes and emissions of trace-gases from point sources (Fioletov et al., 2015). Emissions are retrieved by fitting measured vertical column densities (VCDs) of trace-gases to a three-dimensional function of the wind speed and spatial coordinates. In this study, a plume model generated “synthetic” satellite observations of prescribed emissions to examine the accuracy of the retrieved emissions. The Lagrangian transport and dispersion model FLEXPART (v10.0) modelled the plume from a point source over a multi-day simulation period at a resolution much higher than current satellite observations. The study aims to determine how various assumptions in the retrieval method and local meteorological conditions affect the accuracy and precision of emissions. These assumptions include that the use of a vertical mean of the wind profile is representative of the transport of the plume’s vertical column. In the retrieval method, the VCDs’ pixel locations are rotated around the source based on wind direction so that all plumes have a common wind direction. Retrievals using a vertical mean wind for rotation will be compared to retrievals using VCDs determined by rotating each altitude of the vertical profile of trace-gas using the respective wind-direction. The impact of local meteorological factors on the two approaches will be presented, including atmospheric mixing, vertical wind shear, and boundary layer height. The study aims to suggest which altitude(s) of the vertical profile of winds results in the most accurate retrievals given the local meteorological conditions. The study will also examine the impact on retrieval accuracy due to satellite resolution, trace-gas lifetime, plume source altitude, number of overpasses, and random and systematic errors. Sensitivity studies repeated using a second, “line-density”, retrieval method will also be presented (Adams et al., 2019; Goldberg et al., 2019).</p>

scholarly journals Estimating Subsurface Thermohaline Structure of the Global Ocean Using Surface Remote Sensing Observations

2019 ◽  
Vol 11 (13) ◽  
pp. 1598 ◽  
Author(s):  
Hua Su ◽  
Xin Yang ◽  
Wenfang Lu ◽  
Xiao-Hai Yan
Keyword(s):  
Remote Sensing ◽  
Root Mean Square Error ◽  
Mean Square Error ◽  
Estimation Error ◽  
Satellite Observations ◽  
The Other ◽  
Global Ocean ◽  
Gradient Boosting ◽  
Mean Square ◽  
Thermohaline Structure

Retrieving multi-temporal and large-scale thermohaline structure information of the interior of the global ocean based on surface satellite observations is important for understanding the complex and multidimensional dynamic processes within the ocean. This study proposes a new ensemble learning algorithm, extreme gradient boosting (XGBoost), for retrieving subsurface thermohaline anomalies, including the subsurface temperature anomaly (STA) and the subsurface salinity anomaly (SSA), in the upper 2000 m of the global ocean. The model combines surface satellite observations and in situ Argo data for estimation, and uses root-mean-square error (RMSE), normalized root-mean-square error (NRMSE), and R2 as accuracy evaluations. The results show that the proposed XGBoost model can easily retrieve subsurface thermohaline anomalies and outperforms the gradient boosting decision tree (GBDT) model. The XGBoost model had good performance with average R2 values of 0.69 and 0.54, and average NRMSE values of 0.035 and 0.042, for STA and SSA estimations, respectively. The thermohaline anomaly patterns presented obvious seasonal variation signals in the upper layers (the upper 500 m); however, these signals became weaker as the depth increased. The model performance fluctuated, with the best performance in October (autumn) for both STA and SSA, and the lowest accuracy occurred in January (winter) for STA and April (spring) for SSA. The STA estimation error mainly occurred in the El Niño-Southern Oscillation (ENSO) region in the upper ocean and the boundary of the ocean basins in the deeper ocean; meanwhile, the SSA estimation error presented a relatively even distribution. The wind speed anomalies, including the u and v components, contributed more to the XGBoost model for both STA and SSA estimations than the other surface parameters; however, its importance at deeper layers decreased and the contributions of the other parameters increased. This study provides an effective remote sensing technique for subsurface thermohaline estimations and further promotes long-term remote sensing reconstructions of internal ocean parameters.

scholarly journals Heat waves in Africa 1981–2015, observations and reanalysis

2017 ◽  
Vol 17 (1) ◽  
pp. 115-125 ◽  
Author(s):  
Guido Ceccherini ◽  
Simone Russo ◽  
Iban Ameztoy ◽  
Andrea Francesco Marchese ◽  
Cesar Carmona-Moreno
Keyword(s):  
Heat Wave ◽  
Heat Waves ◽  
Extreme Temperature ◽  
Reanalysis Data ◽  
Maximum Temperature ◽  
Wave Analysis ◽  
Land Area ◽  
Spatial Coverage ◽  
Temperature Records ◽  
Numerical Index

Abstract. The purpose of this article is to show the extreme temperature regime of heat waves across Africa over recent years (1981–2015). Heat waves have been quantified using the Heat Wave Magnitude Index daily (HWMId), which merges the duration and the intensity of extreme temperature events into a single numerical index. The HWMId enables a comparison between heat waves with different timing and location, and it has been applied to maximum and minimum temperature records. The time series used in this study have been derived from (1) observations from the Global Summary of the Day (GSOD) and (2) reanalysis data from ERA-Interim. The analysis shows an increasing number of heat waves of both maxima and minima temperatures in the last decades. Results from heat wave analysis of maximum temperature (HWMIdtx) indicate an increase in intensity and frequency of extreme events. Specifically, from 1996 onwards it is possible to observe HWMIdtx spread with the maximum presence during 2006–2015. Between 2006 and 2015 the frequency (spatial coverage) of extreme heat waves had increased to 24.5 observations per year (60.1 % of land cover), as compared to 12.3 per year (37.3 % of land area) in the period from 1981 to 2005 for GSOD stations (reanalysis).

scholarly journals Chlorine-bearing molecules in molecular absorbers at intermediate redshifts

2019 ◽  
Vol 629 ◽  
pp. A128 ◽  
Author(s):  
S. H. J. Wallström ◽  
S. Muller ◽  
E. Roueff ◽  
R. Le Gal ◽  
J. H. Black ◽  
...  
Keyword(s):  
Molecular Hydrogen ◽  
Chemical Properties ◽  
Abundance Ratio ◽  
The Other ◽  
Trace Gas ◽  
Line Of Sight ◽  
Isotopic Ratios ◽  
Stellar Nucleosynthesis ◽  
Chemical Models ◽  
Intermediate Redshifts

We use observations of chlorine-bearing species in molecular absorbers at intermediate redshifts to investigate chemical properties and 35Cl/37Cl isotopic ratios in the absorbing sightlines. Chloronium (H2Cl+) is detected along three independent lines of sight in the z = 0.89 and z = 0.68 molecular absorbers located in front of the lensed quasars PKS 1830−211 and B 0218+357, respectively. Hydrogen chloride (HCl) was observed only toward PKS 1830−211, and is found to behave differently from H2Cl+. It is detected in one line of sight with an abundance ratio [H2Cl+] / [HCl] ∼1, but remains undetected in the other, more diffuse, line of sight, with a ratio [H2Cl+] / [HCl] > 17. The absorption profiles of these two chlorine-bearing species are compared to other species and discussed in terms of the physical properties of the absorbing gas. Our findings are consistent with the picture emerging from chemical models where different species trace gas with different molecular hydrogen fraction. The 35Cl/37Cl isotopic ratios are measured in the different lines of sight and are discussed in terms of stellar nucleosynthesis.

scholarly journals Observational Evidence of Frontal-Scale Atmospheric Responses to Kuroshio Extension Variability

2015 ◽  
Vol 28 (23) ◽  
pp. 9459-9472 ◽  
Author(s):  
Yi-Hui Wang ◽  
W. Timothy Liu
Keyword(s):  
Kuroshio Extension ◽  
Linear Regression Analysis ◽  
Surface Wind ◽  
Reanalysis Data ◽  
Satellite Observations ◽  
Climate Index ◽  
Boreal Winter ◽  
Atmospheric Response ◽  
Free Atmosphere ◽  
Low Frequencies

Abstract This study investigates the regional atmospheric response to the Kuroshio Extension (KE) using a combination of multiple satellite observations and reanalysis data from boreal winter over a period of at least a decade. The goal is to understand the relationship between KE variations and atmospheric responses at low frequencies. A climate index is used to measure the interannual to decadal KE variability, which leaves remarkable imprints on the mesoscale sea surface temperature (SST). Clear spatial coherence between the SST signals and frontal-scale atmospheric variables, including surface wind convergence, vertical velocity, precipitation, and clouds, is identified by linear regression analysis. Consistent with previous studies, the penetrating effect of the KE variability on the free atmosphere is found. The westward tilt of the atmospheric response above the KE near 500 hPa is revealed. The difference in the associations of frontal-scale air temperature and geopotential height with the KE variability between the satellite observations and the reanalysis data suggests an imperfect interpretation of frontal-scale oceanic forcing on the overlying atmosphere in the reanalysis assimilation system.

When Temporal Certainty Doesn't Help

2020 ◽  
Vol 32 (2) ◽  
pp. 315-325
Author(s):  
Flor Kusnir ◽  
Slav Pesin ◽  
Gal Moscona ◽  
Ayelet N. Landau
Keyword(s):  
Sensory Input ◽  
Temporal Structure ◽  
Sensory Systems ◽  
The Other ◽  
Target Onset ◽  
Detection Thresholds ◽  
Tactile Target ◽  
Temporal Predictability ◽  
Future Events ◽  
The Impact

In a dynamically changing environment, the ability to capture regularities in our sensory input helps us generate predictions about future events. In most sensory systems, the basic finding is clear: Knowing when something will happen improves performance on it [Nobre, A. C., & van Ede, F. (2017). Anticipated moments: Temporal structure in attention. Nature Reviews Neuroscience, 19, 34–48, 2017]. We here examined the impact of temporal predictions on a less-explored modality: touch. Participants were instructed to detect a brief target embedded in an ongoing vibrotactile stimulus. Unbeknownst to them, the experiment had two timing conditions: In one part, the time of target onset was fixed and thus temporally predictable, whereas in the other, it could appear at a random time within the ongoing stimulation. We found a clear modulation of detection thresholds due to temporal predictability: Contrary to other sensory systems, detecting a predictable tactile target was worse relative to unpredictable targets. We discuss our findings within the framework of tactile suppression.

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