Association between ENSO and extremes in total ozone content over northern India

Using daily station total ozone column (TOC) data from the Total Ozone Mapping Spectrometer (TOMS) onboard the Nimbus-7 satellite, an association between the El Niño–Southern Oscillation (ENSO) and extremes in TOC content has been revealed during the period 1979–1993 over northern India in the winter season. From lag-simultaneous correlations of extremes in ozone with Niño 3.4 sea surface temperatures (SSTs), it is seen that, during this season, the highest TOC values show a strong positive relationship at the beginning of the preceding year with the occurrence of the highest values for all the stations. A weak relationship is observed up to the month of July and its sign is then reversed. The negative but weak relationship continues until the occurrence of the event, becoming positive again afterwards. On the contrary, the occurrence of the lowest values shows opposite features. The analysis indicates that the increase in SSTs during the first half of the preceding year is favourable for an increase in the highest values occurring over different stations while the increase in SSTs during the latter half of the preceding year is favourable for an increase in the lowest values of ozone. The lag-simultaneous correlations of the low/high ozone days and the mean TOC values occurring during the winter season also suggest a significant positive relationship for the frequency of the high ozone days at the beginning of the preceding year, becoming weaker as time progresses. Although both features show that the relationship is statistically significant for only a few months of the preceding year, it gives a broad indication of the association between ENSO and the extremes in the TOC amount in addition to local/geographical factors.     

Long-term trends of total ozone content over mid-latitudes of the Northern Hemisphere

Dynamic climatic normals and long-term trends of total ozone in the mid-latitudes of the Northern hemisphere (30°N–60°N) have been determined using data from satellite observations for the period of 1978–2017. The annual course of total ozone is shown as changing over the various regions during the period of observations. The specific features of alteration in the state of the ozone layer are discussed depending on latitude and longitude. Thus, a general increase in total ozone in winter, an increase in spring (with the exception of the northern latitudes of Europe, Asia, and Pacific), and a continuing decrease in summer (with the exception of the northern latitudes of America) during the last 17 years is revealed. The long-term trends of total ozone for different regions and latitude zones (30°N–40°N, 40°N–50°N, and 50°N–60°N) are given depending on season.     

Regional forecast of the UV index with optimized total ozone prediction using satellite observations over East Asia

A regional forecast model of the ultraviolet (UV) index has been developed by using a radiative transfer model and a multiple linear regression model to forecast total ozone over East Asia. This is a difficult and challenging task because of frequent cloud cover and atmospheric aerosols. The new, improved total ozone forecast model was constructed over each grid point in East Asia based on extensive investigation of the correlation between the total ozone and predictors related to the variation in total ozone. Root mean square errors (RMSEs) in the UV index between the forecast and satellite observations from the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) for clear sky conditions range from 0.27 to 1.50 with an average of 0.79 in monthly statistics. Although the patterns of the corrected UV index when applying the cloud modification factor (CMF) and the aerosol modification factor (AMF) compare reasonably well with those of the UV index measured with the Ozone Monitoring Instrument (OMI), the performance depends on the accuracy of forecast for cloud and aerosol optical depth (AOD). Additional consideration of surface albedo and cloud optical depth are required to further refine and improve the accuracy of the prediction.     

On the correction of the total ozone content over Athens,Greece as deduced from satellite observations

The observations with the Total Ozone Mapping Spectrometer ( TOMS) mounted aboard the Nimbus-7 satellite have previously been used to determine the trends of the total ozone amount over Athens, Greece ( 38° N, 24° E), since 1979, for various months ( Varotsos, C. A., and Cracknell, A. P., 1993, International Journal of Remote Sensing, 14, 2053–2059). The total ozone depletion over the 13-year time period showed a strong seasonal variation of the trend from more than 7 per cent in winter to about 2·5 per cent in summer. However, the TOMS instrument measures the back-scattered ultraviolet radiation in order to determine ozone content and is limited to observations above the cloud level. ln the presence of thick cloud the column ozone content is generally underestimated. This underestimation of the total ozone amount is quantitatively examined, especially in the synoptic cases where ozone-rich air has been transported into the lower troposphere. The influence of this underestimation on the total ozone depletion over Athens, Greece, deduced from TOMS observations, is finally attempted.     

Structuring peer assessment: Comparing the impact of the degree of structure on peer feedback content

The present study examines the added value of structuring the peer assessment process, by providing students with a peer feedback template with a varying structuring degree, for the peer feedback content quality in a wiki environment in higher education. The present study took place in the 1st year of a university course in Instructional Sciences (N = 176) and more specifically compared three conditions: no structure peer feedback (control), basic structure peer feedback, and elaborate structure peer feedback condition. Quantitative content analysis of students’ (n = 41) peer feedback messages was performed, and an analysis of (co)variance revealed some discrepancies between the conditions regarding the proportion of peer feedback content categories: (1) peer feedback style, (2) verification type, (3) verification focus, (4) elaboration type, and (5) elaboration focus. This study demonstrated that a higher structuring degree in a peer feedback template during the peer assessment process might have an impact on peer feedback content with respect to the above-mentioned categories; the peer feedback content. Results revealed significant differences between the three conditions regarding the peer feedback content categories. This study illustrated how a practical instructional intervention in the feedback process can increase the potential impact of peer assessment and boost students’ learning in higher education.     

Long-term changes in total ozone column content and its association with stratospheric temperature over two neighbouring tropical Asian stations

This paper focuses on the long-term declining change in total ozone column (TOC) derived from satellite measurements over a 25 year period over two neighbouring tropical Asian sites, Karachi, and Mt Abu. A strong declining trend was observed in TOC at both sites, with a significance level of over 95% and a higher magnitude of 4 to 10 DU per decade in September to December and a weak statistical significance level of below 85% and a lower magnitude of 2 to 4 DU per decade in pre-monsoon months. However, during the monsoon months, a small declining trend of about 1 DU per decade was observed, but this variation is statistically insignificant. Further, the long-term changes in TOC exhibit seasonal dependence with a more negative change of 10 DU per decade in winter over Karachi and 7 DU per decade over Mt Abu. The consequence of such a net long-term declining change in TOC as high as 10 DU per decade is expected to have serious environmental implications due to an overall increase in ground-level solar UV radiation of 18% over the normal values in the tropics. In order to identify some plausible causes of this depletion trend in ozone concentration with stratospheric temperature and solar activity, it is clear that there is a strong relationship between the seasonal dependence of the long-term declining trend of TOC on air temperature at 10 mb or stratospheric cooling. At the same time, there is a less significant long-term variation in TOC due to altered solar activity levels.     

Surface and total ozone investigations in the region of Sofia,Bulgaria

Atmospheric ozone behaviour over Sofia has been investigated with remote-sensing and in situ techniques. Surface ozone and boundary layer observations performed in recent years at three city sites have been analysed. It was found that, in the autumn period, at close meteorological conditions, diurnal ozone variations show stable behaviour from year to year during the analysed period. It may be assumed that the boundary layer and ozone precursor concentrations, which are involved in photochemical ozone formation, keep up their state from year to year at the mentioned conditions. These findings may be interesting when surface ozone trends and climate change influence on ozone are investigated. The analysis of the long-term total ozone content (TOC) variations did not find a total ozone trend in the 1997–2008 period.     

On the relationship between total ozone and temperature in the troposphere and the lower stratosphere

Total ozone and atmospheric temperature are two variables that are closely connected with two important environmental problems: ozone depletion and global warming. Vertical temperature profiles and column ozone data are analysed to explore the relationship between these two variables at various levels in the troposphere and lower stratosphere over Athens, Greece during the period 1992–2004. The results obtained show an out-of-phase relationship between total ozone and temperature in the troposphere and an in-phase relationship in the lower stratosphere. Such a phase change is characteristic of all seasons.     

Roles of ozone depleting substances and solar activity in observed long-term trends in total ozone column over Indian region

An additive time-series decomposition analysis was performed on the Multi Sensor Reanalysis-2 (MSR-2) monthly mean total ozone column (TOC) time-series dataset spanning over 34 years (January 1979–December 2012) for Indian region (0.0–40.0 °N; 67.5–97.5° E). Statistically significant (p-value <0.05) long-term trends in TOC were estimated in the deseasonalized TOC time series. The role of multiple natural and anthropogenic factors: quasi biennial oscillations (QBO), El-Nino Southern Oscillations (ENSO), cyclic variation in solar activity (SA), and ozone depleting substances (ODS) was investigated to explain the long-term trends in TOC over Indian region. Over sub-tropical Indian region (25.0° N– 40.0° N), declining long-term linear trends were estimated, which varied from ?0.30% to ?1.10% per decade. Interestingly a positive long-term linear-trend (0.10–0.30% per decade) was observed over equatorial-tropical part of Indian region. No statistically significant long-term trend was observed for 30mb Equatorial Zonal Winds and Nino 3.4 index – indicators for QBO and ENSO; however, a positive long-term linear trend of magnitude 17.00 ± 1.18% per decade was observed in effective equivalent stratospheric chlorine – a proxy for ODS, and a negative long-term linear trend of magnitude 12.72 ± 2.86% per decade was observed in 10.7 cm Solar Radio Flux – a representative for SF. It is inferred that over the Indian region above tropic of cancer, about 85.00% of the estimated negative long-term linear trend in TOC can be explained by the increase in the stratospheric concentration of ODS; whereas, decrease in the solar activity accounted for 15.00% of the estimated negative long-term linear trend in TOC over sub-tropical Indian region.     

The impact of ozone and acid mist on the spectral reflectance of young Norway spruce trees

Abstract

Spectral reflectance curves in the 400-1110?nm range have been obtained from two-year-old Norway spruce seedlings exposed to varying levels of ozone and acid mist during their two years of growth in controlled environmental chambers. The trees were exposed to l00ppb ozone, 140ppb ozone and 140ppb ozone plus acid mist, while the control group were exposed to filtered air. Two spectral parameters are used to indicate the impact of these pollutants, namely the level of the infrared plateau and the position of the red edge. The infrared plateau has been found to have a higher reflectance as pollutant concentrations increase. This is thought to infer changes within the internal structure of the leaves. The red edge has been found to shift by up to l8?nm at the point of maximum red-edge slope. From both these parameters it is apparent that damage from ozone levels of between 100 and 140 ppb is detectable. This is especially so when the plants are concurrently exposed to acid mist.     

Impact of zonal wind on latitudinal variation of total columnar ozone over the Indian Peninsula

Latitudinal and seasonal variability of total columnar ozone from September 2007 to August 2008 across the Indian longitude sector within 10.5° N to 34.5° N and 70.5° E to 94.5° E using satellite data obtained from Aura Ozone Monitoring Instrument (OMI) of National Aeronautics and Space Administration (NASA) Earth Observing System (EOS) is presented. The total column ozone (TCO) over the area of study shows a gradually varying pattern throughout the year. In the post-monsoon (autumn) and winter months, maximum TCO is observed in the north-western part of the subcontinent while the minimum is often observed towards the east at about the same latitudes. A west–east spatial gradient is clearly observed in autumn months. As winter approaches, a north–south spatial gradient becomes more prominent than the east–west gradient. It has been further observed that TCO does not vary significantly over the entire subcontinent in monsoon.     

A note on the comparison between total ozone from Oslo CTM2 and SBUV satellite data

The results of a comparison between total ozone amounts derived from solar backscatter ultraviolet (SBUV) satellite observations and those calculated from the chemical transport model Oslo CTM2 are presented for the period 2001–2007. Monthly mean total ozone amounts from improved model simulations were used to compute monthly, seasonal and annual zonal means over 10° latitude zones, and compared with respective satellite retrievals over the northern and southern hemispheres. The results show that the improved model simulations slightly underestimate total ozone over the northern hemisphere when compared with the satellites by 1.4% on average, and slightly overestimate total ozone over the southern extra-tropics, middle and high latitudes by 1.6% on average. The mean difference between the model- and satellite-derived total ozone columns from 75°S to 75°N is estimated to be about ?0.3%. A linear regression analysis between the model- and satellite-derived total ozone data shows statistically significant correlations between the two data sets at all latitude zones (about +0.8 in the tropics and more than +0.9 over all other latitudes). The annual cycle of total ozone is shown to be well reproduced by the model at all latitudes.     

First measurements of formaldehyde integral content in the atmosphere using MAX-DOAS in the Moscow region

We present the first observations of formaldehyde (HCHO) atmospheric column performed for Zvenigorod, Moscow region, Russia. The data were retrieved from UV spectra of the scattered solar radiation measured by the multi-axis differential optical absorption spectroscopy (MAX-DOAS) instrument developed by the Japan Agency for Marine-Earth Science and Technology. We developed an algorithm for the HCHO retrieval from these spectra. For retrieval of the HCHO differential slant column densities, we used the DOAS settings used as baseline in the Cabauw Intercomparison Campaign of Nitrogen Dioxide Measuring Instruments (CINDI). The slant column densities of HCHO were converted to vertical column densities (VCDs) using the air mass factors calculated by a radiative transfer model. The determination of HCHO in the reference spectrum used multi-axis measurements.

The variability of the HCHO vertical column in 2010 is analysed. The HCHO vertical column density is larger during east wind directions than during non-east wind directions. This can be associated with the Moscow Megacity influence on air quality at Zvenigorod. The estimation of the Moscow Megacity influence on HCHO abundance at Zvenigorod is around 2.5 × 10¹⁴ molec cm^?2 per 1 km length of trajectory path inside the Moscow Ring Road.

A temperature effect is noticeable in the HCHO VCD. Our data show a statistically significant positive temperature effect in HCHO for the background condition for temperatures from ?5°C to +33°C. The temperature trend in HCHO data at Zvenigorod Scientific Station is about (8.9 ± 2.3) × 10¹⁴ molec cm^?2 (°C)^?1. The increase of the HCHO VCD during increase of the air temperature can be explained by the HCHO formation from non-methane biogenic volatile organic compounds (e.g. isoprene) for which more emission is expected at higher temperatures, and by growth of areas of forest and turf fires.     

On the accuracy of total ozone measurements made with a Dobson spectrophotometer in Athens

Since 1989, total ozone measurements with the Dobson spectrophotometer No. 118 have been made in Athens (38°N, 24°E), which has been suffering from severe air pollution problems during the last fifteen years. These measurements are subject to errors caused by interfering gases that absorb solar ultraviolet radiation in the region of the Dobson instrument's wavelengths (300-400 nm). In the urban area of Athens, the measured S0₂ and N0₂ mixing ratios have been found to lead to total ozone errors of up to 2-5 per cent during the year 1991. To examine the consistency of Dobson measurements, the integrated ozone profiles from a number of ozonesoundings performed at Athens have been used also.     

泄漏同轴电缆在隧道中的辐射特性研究

为了考察泄漏同轴电缆在矩形隧道中的辐射特性,根据泄漏同轴电缆的辐射理论,用时域有限差分方法计算了泄漏同轴电缆开槽口处的电磁场分布,再用射线追踪法分析了在矩形隧道中从泄漏同轴电缆槽口处漏泄出的电波经直射、反射之后所形成的辐射场,结果表明:泄漏同轴电缆辐射出的电磁波可以布满隧道空间,能够弥补传统天线在闭域或半闭域空间中存在...     

带电介质板对电磁波的衰减特性研究

电磁信号在穿透带电介质板时由于电磁波的散射等原因其信号强度会降低,甚至会改变电磁波的极性.为了测量电荷本身对电磁波衰减的影响,设计了带电介质板对电磁波的衰减实验,选取了PP板、PVC板、PMMA板等典型介质板,对电磁波信号衰减进行了实验研究.研究结果表明介质板带电会增强对电磁波的衰减,且随着电量增加,衰减增强.     

Study of aerosols and molecular extinction effects in ultraviolet DIAL remote sensing in the lower atmosphere

Light passing through the atmosphere is scattered and absorbed by the molecules and particles in the atmosphere. This can adversely restrict and limit not only the signal-to-noise ratio (SNR) but also the accuracy and sensitivity of measurements, especially in long-path remote sensing. Usually, in differential absorption lidar (DIAL) techniques, errors are increased mainly because of the different extinction and backscattering properties of the atmosphere at the DIAL probe wavelengths. In this work we have investigated the effects of background aerosol and molecular extinction in DIAL remote sensing in the lower atmosphere for several visibilities at ultraviolet (UV) wavelengths by taking into account the dependence of refraction on the air temperature and pressure. For simplicity, we neglected the spatial inhomogeneity of aerosols in the lower atmosphere. Because of the weak attenuation produced by oxygen and other gaseous atmospheric constituents in this region compared with that from ozone, only ozone is considered as significant among the expected errors. Values for the total attenuation (km^?1) at wavelengths 200–400 nm are tabulated for several values of visibility. The acquired results show that the absorption and scattering by the molecules and aerosols vary with wavelength and visibility. The aerosol attenuation in the UV region varies smoothly and thereby errors caused by aerosol scattering can be neglected in remote sensing by UV-DIAL. In addition, aerosols play a very important role in lidar remote sensing in the lower atmosphere by scattering and absorption of radiation, which is considered as a significant factor. At high altitudes, the aerosol concentration is lower than at the ground; the molecular scattering is important, especially for wavelengths greater than 310 nm, where ozone attenuation is not important. The obtained results are important for accurate UV-DIAL measurements of concentration as well as when real-world signals are not available, for example when designing lidar and simulating or when access to real-world signals is not possible.     

The impact of product characteristics and innovativeness on the benefits of collaboration

Horizontal collaboration is a promising avenue to improve the efficiency of logistical operations. However, the benefits strongly depend on the degree of fit between partners. In this paper, we analyze the impact of the partners' product characteristics on those benefits, focusing on their innovativeness. Companies supplying functional versus innovative products have different requirements in supply chain efficiency and responsiveness, which impacts the benefits that can be reached with a given partner. To assess the collaborative benefits, we use a location–inventory model accounting for the partners' individual interests and the costs revealing the responsiveness level of the supply chain (facilities, transportation, cycle inventory, safety stocks and stock-outs). The model offers a set of Pareto-optimal solutions balancing the partners' costs to support the selection and negotiation process. Finally, we perform numerical experiments in which the partners supply products with identical or different levels of innovativeness and with various demand volumes, leading to valuable managerial insights on the impact of product characteristics on collaborative benefits.     

OFDM符号特性对DCF性能影响研究

认知无线网络由于使用信道频段的长时延特性,OFDM符号时间及Slottime均较大,使得CSMA/CA协议中的SIFS等参数值增大。另外,随着无线局域网络物理层速率的提高,每个OFDM符号携带的数据比特数加大。为评估物理层长时延及高速环境下的DCF性能,基于二维Markov模型得出了CSMA/CA系统吞吐量表达式,数学分析表明系统吞吐量主要由网络节点数、数据包长度、OFDM携带信息比特数、Slottime及OFDM符号时间长度决定。理论计算及仿真测试结果显示,OFDM携带信息比特数越多,Slottime越大,OFDM符号时间长度越长,CSMA/CA的吞吐量性能越低。