Lower Values In Winter Research Articles

Characteristics of hydrogen and oxygen stable isotope ratios in precipitation collected in a snowfall region, Aomori Prefecture, Japan

Characteristics of δ2H and δ18O in precipitation samples collected at 16- to 17-d intervals at three stations at the northern end of Honshu Island, Japan, were investigated. Rokkasho and Ajigasawa stations are approximately 100 km apart, on the Pacific Ocean coast and the Sea of Japan coast, respectively, of Aomori Prefecture. Hakkoda station is between Rokkasho and Ajigasawa stations at 1334 m ASL. Precipitation samples were continuously collected during 2000–2011 at Rokkasho, and during 2003–2006 at Ajigasawa and Hakkoda. At all stations, δ2H and δ18O of the precipitation samples showed weak seasonality, with higher values in summer and lower values in winter. In the summer (June, July, and August), the intercept of the regression line between δ2H and δ18O, that is, the local meteoric water line (LMWL), was lower than that of the global meteoric water line (GMWL) with similar slope, but in winter (December, January, and February), the LMWL intercept was higher than the GMWL intercept with similar slope. Temporal variations of δ18O at the two coastal stations were similar, although the timing of precipitation events was different. At all stations, d-excess values showed clear seasonality, with high values in winter and low values in summer, indicating a seasonal change in the source of the water vapor in air masses arriving over northeast Japan. In winter, d-excess values were higher at Hakkoda than at the other stations, suggesting a precipitation at Hakkoda was derived from water vapor from a remote area of the Sea of Japan. The long-term precipitation data set for δ2H and δ18O obtained in this study will be useful for investigations of regional hydrology and validation of numerical models.

Spectral variation of total column aerosol optical depth over Ranchi: A humid subtropics Indian station

Spectral aerosol optical depth (AOD) measurements, estimated from a hand-held, microprocessorbased sun photometers [MICROTOPS-II (version 2.43)] over Ranchi, India were analyzed from March 2012 to February 2013 (a total of 190 days of clear-sky observations). The results showed seasonal variation with high values in summer and low values in winter. The summer increase is found to be due to the high wind speed producing larger amounts of wind-driven dust particles. The winter AOD values decrease more at higher wavelengths, indicating a general reduction in the number of bigger particles. The amplitude of the observed high AOD values in summer is higher (low during winter) for longer wavelengths, which shows that coarse particles contribute more to the observed variation as compared to sub-micron particles. To characterize the aerosol optical depths, the Angstrom parameters α and β were used.

Thermodynamics and stratification in Xin'anjiang Reservoir(Lake Qiandao)

利用2012年1-12月在新安江水库(千岛湖)6个点位的每月一次的水温及其他环境因子的周年观测资料,分析了水库水温逐月变化、季节变化、垂直分布及温跃层的形成与变化,探讨了温跃层特征量(温跃层深度、厚度、强度)与表层水温、水体透明度的关系.新安江水库表层和中层水温与气温存在显著的线性相关,又以表层水温线性关系最好,而下层水温与气温没有显著相关性,说明下层水温受气温的影响很小,全年处于相对恒温状态.水库表层和中层水温逐月变化明显,呈现夏季最高、春秋季次之、冬季最低的变化趋势,其中中层水温最高值出现的季节较表层水温明显后延,下层水温没有明显的逐月变化和季节变化.水温垂直分布显示,4个季节均存在不同程度的温跃层和温度分层现象,其中水深最深的大坝前水温分层最明显.小金山、三潭岛和大坝前3个典型点位从春季的4月份到冬季的2月份温跃层深度由1.61±0.47 m逐渐增加至39.37±5.35 m,而温跃层厚度和强度则在夏季最高、冬季最低,温跃层随着季节的变化呈现增强稳定减弱消失的周期变化.温跃层深度与水体透明度存在显著正相关,与表层水温存在显著负相关,并基于透明度和表层水温建立温跃层深度的多元线性回归模型.;Based on the in situ investigation data obtained during the period from January to December in 2012 in Xin'anjiang Reservoir, the monthly and seasonal variations, and vertical distributions of water temperature are analyzed. In addition, the thermocline depth, thickness and strength were calculated and the correlations between thermocline depth and water temperature at the surface and secchi disc depth were developed. Significant and positive linear relationships were found between air temperature and water temperature at the surface and middle layers with the marked high correlation coefficient for water temperature at the surface layer. However, no significantly positive relationship was found between air temperature and water temperature at the bottom layer where temperature was maintained almost as an approximate constant indicating that water temperature at the bottom layer was not affected by air temperature. The monthly and seasonal variations of water temperature at the surface and middle layers were as follows:summer > spring, autumn > winter, with a maximum in July or August and a minimum in February or March. The maximal water temperature at the middle layer was lagged to September or October compared to that of the surface layer. In addition, no marked monthly and seasonal variations were found for water temperature at the bottom layer. There is no obvious temperature differences and thermal stratification between the surface and the deep layer water in all four seasons. From April to February, the mean thermocline depth gradually increased from 1.61 ± 0.47 m to 39.37 ± 5.35 m for the three typical sites (Xiaojinshan, Santandao and Dabaqian). In contrast, the thermocline thickness and strength had the highest values in summer and the lowest values in winter. Seasonally, a periodic variation of thermocline from amplification to stabilization, to weakness and further to disappearance was recorded from April to March. Significant and positive linear relationships between the thermocline depth and secchi disc depth, but negative linear relationships between the thermocline depth and water temperature at the surface layer were found. A multiple linear regression model between the thermocline depth and secchi disc depth, water temperature at the surface layer was developed to model the thermocline depth in Xin'anjiang Reservoir.

Sea temperature shapes seasonal fluctuations in seaweed biomass within the Ningaloo coral reef ecosystem

Environmental drivers of seaweed biomass were investigated at Ningaloo, Western Australia, a coral reef ecosystem with negligible anthropogenic influences on seaweeds from fishing, farming, or eutrophication. Periodic surveys of benthic macroalgae occupying seaweed‐dominated beds within the lagoon at two locations (Coral Bay, Tantabiddi) were made during winter, spring, and late summer over a 26 month period. Canopy‐forming Sargassum spp. biomass fluctuated over a seasonal growth—decay cycle, with highest values in the warm summer months (up to 1013 g fresh weight 0.25 m−2 at Coral Bay) and lowest values in winter (down to 155 g fresh weight 0.25 m−2 at Tantabiddi). Conversely, prominent understory seaweed genera Dictyopteris and Lobophora reached peak biomass in winter, when the Sargassum spp. canopy was lowest. Sargassum spp. biomass variation could be attributed largely to time (52%), location (21%), and site (26%), with low variation within individual seaweed beds (1%). Statistical analysis of the influence of five environmental variables (temperature, light, wind‐driven upwelling, rainfall, significant wave height) indicated that location and sea temperature (1 month antecedent to biomass) provided the best explanation for Sargassum spp. biomass fluctuations. While sea temperature is a key driver of seaweed temporal dynamics, heterogeneity at the kilometer scale suggests that spatial context is also important. Given the important role of seaweeds in many ecosystem processes, this strong biophysical coupling between Sargassum spp. biomass and sea temperature suggests that thermal climate change will significantly affect coral reef productivity and biodiversity.

<i>NDVI</i> changes and control factors of the wetland in the Lake Nansi, Shandong Province, in the past 40 years

利用Landsat系列卫星的MSS、TM和ETM+遥感数据,计算了研究区的归一化植被指数(NDVI),并以此为湿地植被活动的指标,研究1973 2011年间该湿地植被变化特征及年内季节变化特征,揭示植被活动在年内和年际变化的控制因子以及湿地植被对于气候变化、人类活动和极端干旱事件的响应特征.结果表明:(1)近40年来南四湖湿地植被各个季节的变化特征不尽相同.春季NDVI呈现先降低后增加的特征,主要先后受到研究区围垦、渔业养殖等人为活动和气候变化(增温)的影响;夏季和冬季的NDVI呈现显著降低趋势,主要受到围垦、渔业养殖等人类活动的影响;秋季NDVI的变化不显著.(2)年内季节变化方面,湿地植被面积和NDVI都呈现单峰的变化特征,从春季开始增加,在夏季末(全年的第202和205 d)达到最大值,然后开始下降,到冬季降至最低.植被的年内季节变化特征主要受到月均温度的控制.(3)干旱在一定程度上不是湖泊湿地NDVI增加的限制因子.干旱导致湖泊水位下降,滨湖滩地及湖底露出,可能会促进湿地植被生长和植被面积的扩大,使得湿地NDVI增加.;The normalized difference vegetation indexes (NDVI) of the wetland in Lake Nansi are calculated on the basis of MSS, TM and ETM + remote sensing data collected by the Landsat satellites. The activities of the wetland vegetations are deduced by these indexes. By studying the characteristics of seasonal vegetation activities of the wetland during 1973-2011, we revealed the control factors of intra-annual and inter-annual vegetation activities. Moreover, our study showed the response characteristics of wetland vegetation to climate changes, human activities and extreme drought events. The results can be summarized as follows:(1) The characteristics of the seasonal variation of wetland vegetation in Lake Nansi are not identical in the past 40 years. The NDVI in spring decreased first and then increased, which may be caused by the climate variation (temperature increase) and human activities such as reclamation and aquaculture in the study area; The NDVI in summer and winter present a significant decreasing trend due to the effects of human activities. However, the variation of the NDVI in autumn is comparatively small. (2) The NDVI and area of wetland vegetation all present single-peaked variation characteristics in term of seasonal variations in one year. They increase in spring and reach the maximum in late summer (the 202nd day and 205th day in the year), then decrease and reach the lowest values in winter. (3) To certain degree, drought is not the limiting factor for NDVI increase. In fact, since drought results in the drawdown of water level of the lake, the beach and lake bottom are exposed. All these factors probably increase the NDVI by prompting the growth of vegetation and enlarging vegetation area in the wetland.

Analysis of photosynthetically active radiation under various sky conditions in Wuhan, Central China

Observations of photosynthetically active radiation (PAR) and global solar radiation (G) at Wuhan, Central China during 2005-2012 were first reported to investigate PAR variability at different time scales and its PAR fraction (F(p)) under different sky conditions. Both G irradiances (I(g)) and PAR irradiances (I(p)) showed similar seasonal features that peaked in values at noon during summer and reached their lower values in winter. F(p) reached higher values during either sunrise or sunset; lower values of F p appeared at local noon because of the absorption effects of water vapor and clouds on long-wave radiation. There was an inverse relationship between clearness index (K(t)) and F(p); the maximum I(p) decreased by 22.3 % (39.7 %) when sky conditions changed from overcast to cloudless in summer (winter); solar radiation was more affected by cloudiness than the seasonal variation in cloudy skies when compared with that in clear skies. The maximum daily PAR irradiation (R(p)) was 11.89 MJ m⁻² day⁻¹ with an annual average of 4.85 MJ m⁻² day⁻¹. F p was in the range of 29-61.5 % with annual daily average value being about 42 %. Meanwhile, hourly, daily, and monthly relationships between R p and G irradiation (R g) under different sky conditions were investigated. It was discovered that cloudy skies were the dominated sky condition in this region. Finally, a clear-sky PAR model was developed by analyzing the dependence of PAR irradiances on optical air mass under various sky conditions for the whole study period in Central China, which will lay foundations for ecological process study in the near future.

Response of soil respiration to temperature and soil moisture: Effects of different vegetation types on a small scale in the eastern Loess Plateau of China

Soil respiration is affected by vegetation and environmental conditions. The purpose of this study was to investigate the effect of vegetation type on soil respiration, temperature and water content, and their correlations on a small scale. We measured soil respiration rate (Rs) over a 3-year period at biweekly intervals in three plots in the eastern Loess Plateau of China, with the same soil texture but different vegetation types: pine forest, grassland, and shrub land. Simultaneously, soil temperature (Ts) at 10 cm depth and soil water content (Ws) within 10 cm depth were measured. The seasonal course of Rs and Ts showed a similar temporal variation in the three plots, with higher values in summer and autumn and lower values in winter and spring. No significant differences (P>0.05) were found between plots, except for Ws. The mean cumulative release of CO2 efflux from March to December was 962.5, 1027.5, and 1166.5 g C m− 2 a− 1 for plots 1, 2, and 3, respectively, with no significant difference between plots. The fitted exponential equations of Rs versus Ts from the 3-year data-set were significant (P < 0.05) with an R2 of 0.72, 0.64, and 0.72 for plots 1, 2, and 3, respectively. The calculated Q10 from the parameters of the fitted equation was 3.57, 3.52, and 3.61, and the R10 was 2.36, 2.03, and 2.37 μmol CO2 m− 2 s− 1 for plots 1, 2, and 3, respectively. Compared with the Ts, the correlations between Rs and Ws were not significant for the three plots. However, if the Ts was above 10°C, then their correlation was significant, and Ws had an impact on Rs. Four combined regression equations including two variables of Ts and Ws could be well established to model correlations between Rs and both Ts and Ws. Our study demonstrated that the exponential and power model fitted best and no significant different correlations of combined equations existed between the three plots. These results show that vegetation type had little impact on Rs, Ts, Ws, and their correlations, as well as on related parameters such as Q10 and R10. Therefore, while doing Rs research in a horizontal patchy vegetation conditions on a small area, the sampling location of measurements should focus on vertical dominant vegetation and ignore patch vegetation so as to reduce field work load.

Atmospheric mercury concentration and chemical speciation at a rural site in Beijing, China: implications of mercury emission sources

Abstract. Continuous measurements of atmospheric mercury concentration and speciation play a key role in identifying mercury sources and its behavior in the atmosphere. In this study, speciated atmospheric mercury including gaseous elemental mercury (GEM), reactive gaseous mercury (RGM) and particle-bound mercury (PBM) were continuously measured at Miyun, a rural site in Beijing, China, from December 2008 to November 2009. The average GEM, RGM and PBM concentrations were found to be 3.22 ± 1.74, 10.1 ± 18.8 and 98.2 ± 112.7 pg m−3, respectively, about 2–20 times higher than the background concentration of the Northern Hemisphere. The results indicated that atmospheric mercury concentrations in northern China were highly affected by anthropogenic emissions. The atmospheric mercury showed obvious seasonal variations, with the highest seasonal average GEM concentration in summer (3.48 ng m−3) and the lowest value in winter (2.66 ng m−3). In autumn and winter a diurnal variation of GEM was observed, with peak levels in the late afternoon till midnight. Most of the high RGM concentration values occurred in the afternoon of all seasons due to the higher oxidation. The PBM concentration was higher in early morning of all seasons because of the the temperature inversion that increases in depth as the night proceeds. The ratio of GEM to CO indicates that residential boilers play an important role in the elevation of GEM in winter. The ratio of RGM to O3 could be an indicator of the contribution of local primary sources. The ratio of PBM to PM2.5 reveals that the air mass from the east and southwest of the site in spring and summer carries more atmospheric mercury. The HYSPLIT back-trajectory analysis indicated that the monitoring site is affected by local, regional and interregional sources simultaneously during heavy pollution episodes. The results from the potential source contribution function (PSCF) model indicate that the atmospheric transport predominantly from the northwest contributes to the elevated atmospheric mercury in winter and autumn, while the North China Plain (NCP) region and the northern part of the Yangtze River Delta (YRD) region are the major source areas for mercury pollution in spring and summer.

Estimations of net primary productivity and evapotranspiration based on HJ-1A/B data in Jinggangshan city, China

Net primary productivity (NPP) and evapotranspiration (ET) are two key variables in the carbon and water cycles of terrestrial ecosystems. In this study, to test a newly developed NPP algorithm designed for HJ-1 A/B data and to evaluate the usage of HJ-1 A/B data in the quantitative assessment of environments, NPP and ET in Jinggangshan city, Jiangxi province, are calculated using HJ-1 A/B data. The results illustrate the following: (1) The NPP and ET in Jinggangshan city in 2010 both show obvious seasonal variation, with the highest values in summer and the lowest values in winter, and relatively higher values were observed in autumn than in spring. (2) The spatial pattern indicates that the annual NPP is high in the southern area in Jinggangshan city and low in the northern area. Additionally, high NPP is distributed in forests located in areas with high elevation, and low NPP is found in croplands at low elevations. ET has no significant north-south difference, with high values in the southeast and northwest and low values in the southwest, and high ET is distributed in forests at low elevations in contrast to low ET in forests in high-elevation areas and in cropland and shrub grassland in low-elevation areas. (3) Compared to the MODIS product, the range of HJ-1 NPP is larger, and the spatial pattern is more coincident with the topography. The range of HJ-1 ET is smaller than that of the MODIS product, and ET is underestimated to some extent but can reflect the effect of topography. This study suggests that the algorithm can be used to estimate NPP and ET in a subtropical monsoon climate if remotely sensed images with high spatial resolution are available.

Empirical studies of cloud effects on ultraviolet radiation inCentralChina

ABSTRACTGlobal solar radiation (G) and ultraviolet radiation (UV) observed at Wuhan, China from 2006 to 2012 have been used to investigate the temporal variability of both radiant fluxes and theUV/G ratios (FUV) at different time scales for the first time in central China. Clearness index (Kt) was used to study the cloud effects onFUVin each month under different sky conditions. It turned out thatFUVreached higher values in summer and lower values in winter;FUValso increased generally with cloudiness. AUVmodel for cloud‐free condition was developed by studying the dependence of hourlyUVirradiations on the relative optical air mass (m), which has been assessed through the statistical indices: mean bias error (mbe), mean‐absolute bias error (mabe) and root‐mean‐square error (rmse) whose values were 0.32, 7.3 and 8.64%, respectively.UVclearness index, m and Kt were further used for analysing the cloud effects, and differentUVmodels under any sky conditions have been established and validated. Meanwhile, as a modulation for different sky conditions, both cloud modification factors were also used in the construction of a new type ofUVmodel. Finally, by comparing the statistical indices from different models, the most suitable model was chosen for validating at Wuhan University (WHU) and two other sites in different regions of China under any atmospheric conditions, which suggested that the proposed model should be modified to account for local differences to produce better estimations in larger areas.

Influence of the Sea-Land Interface Moisture Flux on Reference Evapotranspiration in Liaohe Delta, Northeast China

This study investigates the association between the sea-land interface moisture flux and reference evapotranspiration during 1971-2010 in Liaohe Delta, Northeast China, which moisture flux is derived from NCAR/NCEP reanalysis I data and reference evapotranspiration is calculated by Penman-Monteith equation. The result shows that the sea-land interface moisture flux presents a seasonal variation with the highest value in summer and the lowest value in winter. The sea-land interface moisture flux and reference evapotranspiration show significantly positive correlation in spring and autumn and significantly negative correlation in summer. Consistent with the past field experiments, the sea-land moisture flux suppresses reference evapotranspiration in summer. The positive correlation reveals that the sea-land moisture flux, especially in surface sublayer, facilitates reference evapotranspiration in spring and autumn. Regressions analysis demonstrate that reference evapotranspiration increases when moisture flux of surface-to-850-hPa sublayer increases until reaches the threshold (67-75 kg/ms), and the opposite trend appears when moisture flux exceeds the threshold.

남해동부해역의 표층 수괴 변화에 따른 환경요인과 식물플랑크톤 군집의 계절적 변화

We investigated the seasonal succession of phytoplankton assemblages in the eastern part of the South Sea of Korea in relation to surface water masses. The study areas are under the direct influence of the Tsushima Warm Current (TCW) throughout the whole year, with its strength known to be seasonally variable. The region is also influenced by coastal waters (CW) driven from the South Sea of Korea and East China Sea, particularly in summer, as indicated by low salinity in the surface water. Nutrient property of the TCW can reveals whether the origin of the TCW is the nutrient-rich Kuroshio Current or the oligotropic Taiwan Warm Current. Surface chlorophyll-a (Chl-a) concentrations displayed a large seasonal variation for all stations, with high values found in spring and autumn and low values in summer and winter. At station M (offshore) and P (intermediate location between M and R), Chl-a concentrations in October were higher than those in March, when spring bloom normally occurs. This may be related to deeper mixed layer depths in October. Diatoms dominated under conditions of high nutrient supply in which Chaetoceros spp. and Skeletonema costatum-like spp. were abundant. S. costatum-like spp. dominated at stations R (onshore station) and P in December when there was greater nutrient supply, especially of phosphate. Flagellates and dinoflagellates dominated at all three stations after diatoms blooms. Dominant species were Scrippsiella trochoid in April and Ceratium furca in October at station R, and Gyrodinium spp. and Gymnodinium spp. at station M during summer, when the effect of the oligotropic Taiwan Warm Current and the oligotropic coastal water from East China Sea were strong. Redundancy analysis showed clear seasonal successions in the phytoplankton community and environmental conditions, in which both principal components 1 and 2 accounted for 69.6% of total variance. Our results suggested that environmental conditions seemed to be determined by the origin of the TCW and the relative seasonal strength of the water masses of the TCW and CW, which may affect phytoplankton growth and compositions in the study area.

Photosynthetically active radiation and its relationship with global solar radiation in Central China

Photosynthetically active radiation (PAR) and other solar components were observed for a period of 3 years at Wuhan, China to determine for the first time the temporal variability of PAR fraction [PAR/G (G here stands for global solar radiation)] and its dependence on different sky conditions in Central China. PAR, G and PAR/G showed similar seasonal features that peaked in summer and reached their lowest values in winter. The seasonal PAR/G ranged from 1.70 E MJ(-1) (winter) to 2.01 E MJ(-1) (summer) with an annual mean value of 1.89 E MJ(-1). Hourly values of PAR/G increased from 1.78 to 2.11 E MJ(-1) on average as sky conditions changed from clear to cloudy. Monthly mean hourly PAR/G revealed a diurnal variation, with highest values observed around sunrise and sunset, slightly higher PAR fractions were also found around noon for most months. The effect of daylength on PAR/G was also studied and no significant impact was found. Three models were developed to estimate PAR from G. These models consisted of atmospheric parameters that were found to cause substantial changes of PAR/G, such as sky clearness, brightness, path length and the sky clearness index. The estimations obtained from different models were very close to the measured values with maximum relative errors below 8 % (hourly values) in Wuhan. The models were not only tested at seven radiation stations in Central China, but also verified in six stations with different climates in China. The models were found to estimate PAR accurately from commonly available G data in Central China; however, the results also implied that the models need to be modified to account for local climatic conditions when applied to the whole country.

Soil Moisture Retrieval in the Heihe River Basin Based on the Real Thermal Inertia Method

Remotely sensed thermal inertia method has been recognized as a promising approach for land surface soil moisture retrieval from the early 1970's. In order to estimate the land surface soil moisture in arid regions, a real thermal inertia (RTI) model was formulated based on the heat conduction equation and an approximated energy budget equation at the land surface using the land surface temperature and reflectance measured by Moderate Resolution Imaging Spectroradiometer (MODIS). The soil thermal inertia of Heihe River Basin (HRB) was retrieved based on the RTI model. Furthermore, using a thermal inertia-soil moisture model along with auxiliary data such as soil texture and bulk density, land surface soil moisture was estimated. The results were verified experimentally using the observations made at three automatic weather stations (AWS). The coefficient of the correlation between the retrieved values of soil thermal inertia and measured ones was with above R=0.6 and the root mean square error of soil moisture was 0.072 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> . The soil moisture in the HRB exhibits a seasonal variation with higher values in summer and autumn and lower values in winter and spring, and also exhibits considerable spatial variation with higher values in the upstream district and lower values in the downstream district.

The evaluation of the integrated water vapour annual cycle over the Iberian Peninsula from EOS‐MODIS against different ground‐based techniques

AbstractThe annual cycle of precipitable water vapour is inferred from the MODIS thermal infrared (IR) and near‐infrared (NIR) satellite products under clear‐sky conditions for the period 2002–2008 at 18 sites in the Iberian Peninsula, with the aim to evaluate the capabilities of both algorithms. The article presents these results in relation to ground observations using different techniques (GPS, sunphotometer, radiosounding), with a special emphasis on GPS. At all sites the annual cycle presents the typical shape with low values in winter (minimum ∼1 cm) and high values in summer (maximum ∼3 cm), and a smaller cycle amplitude at continental sites than at coastal sites. The satellite results clearly depict the north–south gradient, as well as singular patterns such as the July minimum characterizing the most southern stations. The differences in the monthly means with respect to ground observations are mostly underestimations, ranging between a few percent to 40%, being generally larger in winter than in summer. Overall, NIR performs better than IR, especially in the wintertime. However, NIR presents overestimations in summer that can reach up to 30%. The comparison results of the annual cycle appear much more heterogeneous within coastal than continental areas, in particular for the Mediterranean region. It was found that the performance of IR algorithm is strongly influenced by the seasonal variations, a dependence which is much weaker in NIR retrievals. The time‐coincident comparison shows that best MODIS/GPS agreement is found for continental regions (r.m.s.∼0.3) for both methods. The largest regression biases and rms differences are found at the Mediterranean sites. The influence of sampling in the evaluation of the MODIS annual cycle was shown to affect mainly winter values. Errors induced by the retrieval accuracy and those induced by sampling deficiencies sometimes add up or compensate each other partially or totally.

Columnar aerosol properties from sun-and-star photometry: statistical comparisons and day-to-night dynamic

Abstract. This work presents the first analysis of long-term correlative day-to-night columnar aerosol optical properties. The aim is to better understand columnar aerosol dynamic from ground-based observations, which are poorly studied until now. To this end we have used a combination of sun-and-star photometry measurements acquired in the city of Granada (37.16° N, 3.60° W, 680 m a.s.l.; South-East of Spain) from 2007 to 2010. For the whole study period, mean aerosol optical depth (AOD) around 440 nm (± standard deviation) is 0.18 ± 0.10 and 0.19 ± 0.11 for daytime and nighttime, respectively, while the mean Angström exponent (α) is 1.0 ± 0.4 and 0.9 ± 0.4 for daytime and nighttime. The ANOVA statistical tests reveal that there are no significant differences between AOD and α obtained at daytime and those at nighttime. Additionally, the mean daytime values of AOD and α obtained during this study period are coherent with the values obtained in the surrounding AERONET stations. On the other hand, AOD around 440 nm present evident seasonal patterns characterised by large values in summer (mean value of 0.20 ± 0.10 both at daytime and nighttime) and low values in winter (mean value of 0.15 ± 0.09 at daytime and 0.17 ± 0.10 at nighttime). The Angström exponents also present seasonal patterns, but with low values in summer (mean values of 0.8 ± 0.4 and 0.9 ± 0.4 at day- and night-time) and relatively large values in winter (mean values of 1.2 ± 0.4 and 1.0 ± 0.3 at daytime and nighttime). These seasonal patterns are explained by the differences in the meteorological conditions and by the differences in the strength of the aerosol sources. To take more insight about the changes in aerosol particles between day and night, the spectral differences of the Angström exponent as function of the Angström exponent are also studied. These analyses reveal increases of the fine mode radius and of the fine mode contribution to AOD during nighttime, being more remarkable in the summer seasons. These variations are explained by the changes of the local aerosol sources and by the meteorological conditions between daytime and nighttime, as well as aerosol aging processes. Case studies during summer and winter for different aerosol loads and types are also presented to clearly illustrate these findings.

Study of aerosol optical depth, ozone, and precipitable water vapour content over Sinhagad, a high-altitude station in the Western Ghats

This article reports the results of a study related to variations in columnar aerosol optical depth (AOD), total column ozone (TCO), and precipitable water content (PWC) over a high-altitude station, Sinhagad (18° 21′ N, 73° 45′ E, 1450 m above mean sea level (AMSL)), employing a microprocessor-based total ozone portable spectrometer, MICROTOPS-II, comprising both a sun photometer and ozonometer, during November 2009–April 2010. The aerosol optical depth at 500 nm (AOD500 nm) portrayed seasonal variation with higher values (0.39) in summer and lower values (0.15) in winter. The TCO and PWC also exhibited lower values in winter and started increasing by the pre-monsoon season. The Ångström wavelength exponent, α, was found to be high (1.79) during February, indicating the relative dominance of accumulation-mode particles. During the summer season, the lower value (0.94) of the Ångström wavelength exponent indicates the relative dominance of coarse-mode particles. The ground-based observations from MICROTOPS-II revealed good correlation with satellite observations of the Moderate Resolution Imaging Spectroradiometer (MODIS) and Ozone Monitoring Instrument (OMI). The observed short-wave solar flux at the bottom of the atmosphere decreased due to aerosol extinction and was found to be 19 and 78 W m–2 for the winter and pre-monsoon seasons, respectively. This implies that greater concentrations of accumulation-mode particles – which are due to local anthropogenic sources – affected the down-welling radiation than those from natural sources – which are due to long-range transport processes – over the experimental location.

Chemical and radioactive composition of bulk deposition in Málaga (Spain)

Chemical and radioactive composition of bulk deposition samples, which were collected monthly over a 5 year period (January 2007 until 31 December 2011) at a site located 30 m.a.l. in Málaga (4°28′ 8″W; 36°43′ 40″N) have been analysed. All samples were analysed for pH, major ions and gamma radionuclides. The average pH of bulk deposition was 6.4. Cl− and SO42− were the main anions, while Ca+ and Na+ were the main cations. Significant correlations were found in soil-derived species among Ca2+, Mg2+ and K+ and sea-salt species between Na+ and Cl−. Other relatively good correlations were also observed between acidic anions (SO42−andNO3−) and crustal-derived cations (Ca2+, Na+, K+). Sources of the major ions were assessed based on the enrichment factor method. The radionuclides present in all samples are 7Be and 210Pb and 40K appears in 50% of the samples. Relatively poor correlations were observed between the specific activities of gamma radionuclides and the major ions. The temporal variations of major ions and radionuclides exhibit similar seasonal behaviour with low values in winter–autumn months and maximum values in spring–summer months. The fluxes of major ions and gamma radionuclides have been discussed with meteorological factors controlling depositions.

Analysis of the air pollution climate at a background site in the Po valley

The Po valley in northern Italy is renowned for its high air pollutant concentrations. Measurements of air pollutants from a background site in Modena, a town of 200 thousand inhabitants within the Po valley, are analysed. These comprise hourly data for CO, NO, NO(2), NO(x), and O(3), and daily gravimetric equivalent data for PM(10) from 1998-2010. The data are analysed in terms of long-term trends, annual, weekly and diurnal cycles, and auto-correlation and cross-correlation functions. CO, NO and NO(2) exhibit a strongly traffic-related pattern, with daily peaks at morning and evening rush hour and lower concentrations over the weekend. Ozone shows an annual cycle with a peak in July due to local production; notwithstanding the diurnal cycle dominated by titration by nitrogen oxide, the decreasing long term trend in NO concentration did not affect the long term trend in O(3), whose mean concentration remained steady over the sampling period. PM(10) shows a strong seasonality with higher concentration in winter and lower concentration in summer and spring. Both PM(10) and ozone show a marked weekly cycle in summer and winter respectively. Regressions of PM(10) upon NO(x) show a consistently greater intercept in winter, representing higher secondary PM(10) in the cooler months of the year. There is a seasonal pattern in primary PM(10) to NO(x) ratios, with lower values in winter and higher values in summer, but the reasons are unclear.

Long-term analysis of Hubbard Brook stable oxygen isotope ratios of streamwater and precipitation sulfate

In response to decreasing atmospheric emissions of sulfur (S) since the 1970s there has been a concomitant decrease in S deposition to watersheds in the Northeastern U.S. Previous study at the Hubbard Brook Experimental Forest, NH (USA) using chemical and isotopic analyzes (\( \delta^{34} {\text{S}}_{{{\text{SO}}_{4} }} \)) combined with modeling has suggested that there is an internal source of S within these watersheds that results in a net loss of S via sulfate in drainage waters. The current study expands these previous investigations by the utilization of δ18O analyzes of precipitation sulfate and streamwater sulfate. Archived stream and bulk precipitation samples at the Hubbard Brook Experimental Forest from 1968–2004 were analyzed for stable oxygen isotope ratios of sulfate (\( \delta^{18} {\text{O}}_{{{\text{SO}}_{4} }} \)). Overall decreasing temporal trends and seasonally low winter values of \( \delta^{18} {\text{O}}_{{{\text{SO}}_{4} }} \) in bulk precipitation are most likely attributed to similar trends in precipitation \( \delta^{18} {\text{O}}_{{{\text{H}}_{2} {\text{O}}}} \) values. Regional climate trends and changes in temperature control precipitation \( \delta^{18} {\text{O}}_{{{\text{H}}_{2} {\text{O}}}} \) values that are reflected in the \( \delta^{18} {\text{O}}_{{{\text{SO}}_{4} }} \) values of precipitation. The significant relationship between ambient temperature and the \( \delta^{18} {\text{O}}_{{{\text{H}}_{2} {\text{O}}}} \) values of precipitation is shown from a nearby site in Ottawa, Ontario (Canada). Although streamwater \( \delta^{18} {\text{O}}_{{{\text{SO}}_{4} }} \) values did not reveal temporal trends, a large difference between precipitation and streamwater \( \delta^{18} {\text{O}}_{{{\text{SO}}_{4} }} \) values suggest the importance of internal cycling of S especially through the large organic S pool and the concomitant effect on the \( \delta^{18} {\text{O}}_{{{\text{SO}}_{4} }} \) values in drainage waters.