Variations In Surface Solar Radiation Research Articles

Accelerated surface brightening in China: The decisive role of reduced anthropogenic aerosol emissions

A profound comprehension of the key determinants behind the fluctuations in surface solar radiation (SSR) over decadal timescales is essential for advancing the fields of energy meteorology, climatology, and solar resources. While there is a general agreement among prior research on the significant impact of aerosols on SSR, a granular understanding of the specific influence that varying aerosol types exert on SSR remains elusive. This investigation delves into the respective impacts of aerosols and cloud radiative effects across China, utilizing data from the Clouds and the Earth's Radiant Energy System (CERES). It further dissects the distinct impacts of different aerosol types on the decadal-scale variations in SSR, employing spectral aerosol optical depths derived from the MODIS aerosol products. The findings reveal a predominantly positive trend in SSR, ranging from 1.5 to 2.5 W/m2/yr between the years 2011 and 2022 for the majority of China's regions. However, certain areas within Northeast and Western China exhibit a decline in SSR exceeding −1 W/m2/yr. Notably, in Eastern China, a downward trend in aerosol radiative effect is observed, with a pronounced reduction of approximately −2 W/m2/yr noted specifically during the summer in Northern China. The study infers that the reduction in urban industrial emissions and biomass burning aerosols is linked to the acceleration of the brightening phenomenon in China. Our results underscore that stringent regulation of anthropogenic emissions could yield dual benefits: environmental amelioration and an upsurge in solar resource. These insights merit serious contemplation in the formulation of future policy and decision-making frameworks.

Trend of surface solar radiation over China in relation to changing synoptic patterns

A comprehensive understanding of the relationship between atmospheric circulations and variations in surface solar radiation (SSR) is important for effectively utilizing solar resources and assessing climate change impacts. Here, we identify four synoptic patterns by T-mode principal component analysis method during 1980–2020 associated with the spatio-temporal variations of SSR in China, including geopotential height anomalies of west-high-east-low (Type 1), north-high-south-low (Type 2), east-low-west-high (Type 3), and north-low-south-high (Type 4). For the whole summer, there are more days of Type 1 and Type 2, accounting for 28.74 % and 28.58 % respectively. In particular, Type 1 experiences positive anomalies in cloud cover, water vapor and significantly reduced SSR reaching the Earth’s surface. Type 2 pattern is characterized with low (high) anomalies of SSR over the Yangtze River Basin (Northeast China). And the north of the Yangtze River Basin is controlled by a northerly dry and cold airflow, leading to low cloudiness and precipitation with increased SSR reaching the ground in Type 3. Type 4 pattern exhibits a negative (positive) SSR anomalies in the Yellow River Basin (the Yangtze River Basin and Northeast China). Notably, the reduction of summer SSR in China since the 1980s is largely explained by the long-term changes of Type 2 and Type 4 synoptic patterns. These findings improve the understanding of the relationship between atmospheric circulations and SSR, and provide a scientific basis for policy planning of solar energy and dual-carbon targets in China.

An effort to distinguish the effects of cloud cover and aerosols on the decadal variations of surface solar radiation in the Northern Hemisphere

Surface solar radiation (SSR) serves as the primary energy source on Earth. However, a relative lack of research systematically quantifies long-term SSR variations and their driving factors based on complete and reliable baseline data. This paper presents a new assessment of the Northern Hemisphere/regional SSR variations and the influence of total cloud cover (TCC) on these variations, based on the latest reconstructed SSR gridded dataset. We also address multicollinearity among multiple aerosol types and quantify the effects of multiple aerosol/precursors on SSR variability using a partial least squares regression model. The results indicate that TCC is not the predominant driver of longer-term SSR variations, known as ‘dimming’ and ‘brightening’. The variations of NH3 and SO2 primarily drive inter-decadal SSR variations in North America, while the variations of SO2 and NO X mainly influence inter-decadal SSR variations in Europe.

An integrated and homogenized global surface solar radiation dataset and its reconstruction based on a convolutional neural network approach

Abstract. Surface solar radiation (SSR) is an essential factor in the flow of surface energy, enabling accurate capturing of long-term climate change and understanding of the energy balance of Earth's atmosphere system. However, the long-term trend estimation of SSR is subject to significant uncertainties due to the temporal inhomogeneity and the uneven spatial distribution of in situ observations. This paper develops an observational integrated and homogenized global terrestrial (except for Antarctica) station SSR dataset (SSRIHstation) by integrating all available SSR observations, including the existing homogenized SSR results. The series is then interpolated in order to obtain a 5∘ × 5∘ resolution gridded dataset (SSRIHgrid). On this basis, we further reconstruct a long-term (1955–2018) global land (except for Antarctica) SSR anomaly dataset with a 5∘ × 2.5∘ resolution (SSRIH20CR) by training improved partial convolutional neural network deep-learning methods based on 20th Century Reanalysis version 3 (20CRv3). Based on this, we analysed the global land- (except for Antarctica) and regional-scale SSR trends and spatiotemporal variations. The reconstruction results reflect the distribution of SSR anomalies and have high reliability in filling and reconstructing the missing values. At the global land (except for Antarctica) scale, the decreasing trend of the SSRIH20CR (−1.276 ± 0.205 W m−2 per decade) is smaller than the trend of the SSRIHgrid (−1.776 ± 0.230 W m−2 per decade) from 1955 to 1991. The trend of the SSRIH20CR (0.697 ± 0.359 W m−2 per decade) from 1991 to 2018 is also marginally lower than that of the SSRIHgrid (0.851 ± 0.410 W m−2 per decade). At the regional scale, the difference between the SSRIH20CR and SSRIHgrid is more significant in years and areas with insufficient coverage. Asia, Africa, Europe and North America cause the global dimming of the SSRIH20CR, while Europe and North America drive the global brightening of the SSRIH20CR. Spatial sampling inadequacies have largely contributed to a bias in the long-term variation of global and regional SSR. This paper's homogenized gridded dataset and the Artificial Intelligence reconstruction gridded dataset (Jiao and Li, 2023) are both available at https://doi.org/10.6084/m9.figshare.21625079.v1.

Intraseasonal and synoptic modulation of diurnal surface solar radiation over Reunion island in the South-West Indian Ocean

Understanding the space-time variability of Surface Solar Radiation (SSR) is mandatory for the prediction and, eventually, the skillful forecasting of photovoltaic energy production. This paper addresses the modulation of local-scale SSR over Reunion, a tropical island in the South-West Indian Ocean, by the leading modes of climate variability influencing both regional-scale and local-scale atmospheric convection and its associated cloud cover. Analyses focus on synoptic (tropical cyclones [TCs], synoptic convective regimes, including Tropical-Temperate Troughs [TTTs]) and intraseasonal (Madden-Julian Oscillation [MJO]) timescales. The SSR intra-daily variability is first assessed by a diurnal classification of SARAH-E satellite SSR data, and it is then related to the climate conditions mentioned above. SSR anomalies are found larger (smaller) on the windward (leeward) side of Reunion and in the summer (winter) season. The island-scale “cloudy” conditions can typically last 1 or 2 days. Nearby TCs can strongly reduce SSR by up to 50% on average, depending on their distances from Reunion, their sizes, and particularly, their longitudinal positions, which is observed for the first time. Nearby TCs are associated with significant negative SSR anomaly when located west of Reunion but with less significant or even positive anomaly when located east of the island. Synoptic convective regimes (the intraseasonal MJO) have a relatively weaker impact on SSR, with a value up to 13% (5%) of the mean value. Potential interactions between these SSR modulators are also investigated to understand better and eventually predict the mechanisms likely to modulate SSR (and thus photovoltaic electricity production) at sub-seasonal timescales.

Correction to: Intraseasonal and synoptic climate variability of surface solar radiation over South‐West Indian Ocean: Regional climate modelling

Correction to: Intraseasonal and synoptic climate variability of surface solar radiation over <scp>South‐West</scp> Indian Ocean: Regional climate modelling

Disentangling Aerosol and Cloud Effects on Dimming and Brightening in Observations and CMIP6

AbstractPeriods of dimming and brightening have been recorded in observational datasets of surface solar radiation (SSR) between the mid‐20th century and present day. Atmospheric components affect SSR, including aerosols and clouds, though studies disagree somewhat about the relative effect of each component in different regions. Current Earth system models (ESMs) are unable to simulate observed trends in SSR. This study includes an investigation into observed SSR variations between 1961 and 2014 and an evaluation of the effects of cloud cover variations and impacts of aerosol extinction, using timeseries of SSR and cloud cover from in‐situ measurements. Historical simulations by 42 ESMs participating in the Coupled Model Intercomparison Project phase 6 (CMIP6) have also been studied and compared to observations. The observational study indicates that cloud cover has had a dampening effect on the variations of SSR and that emissions of aerosol and aerosol precursors are the main cause of the general trends in observed SSR in four regions—China, Japan, Europe, and the United States—during 1961–2014. The study of simulated SSR in CMIP6 yields the conclusion that current ESMs remain unable to simulate the magnitude of observed dimming and brightening in China, Japan, and the United States, but that the European SSR trends between 1961 and 2014 are fairly well reproduced in the ESMs. A rough quantification of the regional surface radiation extinction efficiency of aerosol and precursor emissions in the simulations is found to agree with observed values in Europe, but not in the other three regions.

Variability of surface solar radiation under clear skies over Qinghai-Tibet Plateau: Role of aerosols and water vapor

Surface solar radiation (SSR) plays a vital role in the global energy cycle and the interaction between the earth and atmosphere. It has a significant impact on climate change. Aerosols and water vapor are important factors affecting the variations in clear-sky SSR. This study analyzed the effects of aerosols and water vapor on clear-sky SSR in the Qinghai-Tibet Plateau (QTP), one of the most sensitive areas to global climate change, over the past 20 years. The results show that the 87.0% of the monthly clear-sky SSR over QTP can be explained by the monthly aerosols and water vapor. The aerosol direct radiative effect (ADRE) value in most QTP areas (93.35%) is lower than −10 W m−2. The effect of water vapor on the monthly value of clear-sky SSR is greater than that of aerosols. The reduced clear-sky SSR (about 61.36% of QTP areas) in the past 20 years is mainly concentrated at the south–north boundary. The significant increases in sulfate and carbonaceous aerosols from India have contributed to the decrease in clear-sky SSR in the South. Moreover, the increasing water vapor influx from the southern boundary is also an important reason for the reduction in clear-sky SSR in the South and North. The results also indicate that the decrease in dust aerosols, originating from the Taklamakan and Qaidam Deserts, results in the increase in clear-sky SSR in the Northeast.

Intraseasonal and synoptic climate variability of surface solar radiation over South‐West Indian Ocean: Regional climate modelling

AbstractThe abundant surface solar radiation (SSR) over South‐West Indian Ocean (SWIO) presents significant temporal variability. To characterize this temporal variability is important for the application of solar energy, such as photovoltaic industry. This article studied the intraseasonal and synoptic climate variability of SSR by regional climate modelling over SWIO region. The regional climate model, RegCM4's skill is first evaluated through analysing the seasonal mean SSR with the precipitation, near surface temperature and total cloud cover in austral summer and winter. The basic validation of those simulated parameters with the reference data showed model's performance on SSR. The austral summer (November–February) 1999–2008 was chosen to search the Madden–Julian Oscillation patterns and tropical temperate troughs which are the major expression of intraseasonal and synoptic climate variability. The circulation, moisture fluxes, and radiation fluxes have been checked at the beginning for RegCM4's input dataset (ERA‐Interim) to find the signals. Then, the output simulation results were taking into account to see if the model can reproduce the intraseasonal and synoptic climate variability or not. SSR from SARAH‐E (CM SAF@5 km) as the reference dataset in the end has been used to validate the simulated patterns, which showed that the eastward SSR anomalies propagation and negative SSR anomalies bands can be observed in RegCM4 and the according satellite dataset. These results identified and explained SSR's intraseasonal and synoptic climate variability over SWIO region, which provide a way through RegCM to perform SSR's evaluation and prediction.

ИЗМЕНЕНИЯ СОЛНЕЧНОЙ РАДИАЦИИ НА ТЕРРИТОРИИ СЕВЕРНОЙ ЕВРАЗИИ В ТЕПЛОЕ ВРЕМЯ ГОДА ЗА МНОГОЛЕТНИЙ ПЕРИОД ПО ДАННЫМ ИЗМЕРЕНИЙ И МОДЕЛИ РЕКОНСТРУКЦИИ

A reconstruction model of surface solar radiation (SR) is developed. The results of reconstructing the interannual SR variability for the period of 1968-2016 are tested against the observations at MSU (Lomonosov Moscow State University) Meteorological Observatory for the warm season (May-September), the comparison showed a good agreement (the coefficient of determination R2 = 0.8). The analysis of temporal variations in SR over Northern Eurasia (40-80 N; 10 W-180 E) due to various factors revealed that in most cases there has been a trend toward an SR increase since 1979. In addition, it is demonstrated that the long-term SR variability over Northern Eurasia was effectively explained by variations in the cloud transmission of Sr, except for the polluted regions of Siberia and China and several stations in Northern Europe, where the aerosol factor dominates in some cases.

Impacts of the seesaw mode between the Indian and East Asian summer monsoons on interannual variations in surface solar radiation across the low‐latitude highlands of China

AbstractThe relationship between the seesaw mode that connects the Indian summer monsoon (ISM) and East Asian summer monsoon (EASM), and variations in summer surface solar radiation (SSR) across the low‐latitude highlands of China (CLLH), was investigated using atmospheric reanalysis and NOAA global gridded precipitation and outgoing longwave radiation datasets. Singular value decomposition, correlation analysis, and composite analysis were employed. The results indicate that the interannual variations in summer SSR in the CLLH are significantly modulated by the seesaw mode that connects the ISM with the EASM. During the boreal summer, the CLLH SSR variability is positively correlated with ISM intensity, but negatively correlated with EASM intensity. When a strong ISM and a weak EASM occur together, significant anomalous northeasterly winds appear over the CLLH, which reduces the moisture supply to the region from the Bay of Bengal. In addition, significant anomalous descending motion dominates the CLLH, leading to significant negative relative humidity anomalies over the CLLH. Consequently, water vapour, total liquid water form column clouds and high cloud cover decreased significantly over the CLLH, resulting in a higher CLLH SSR than average. Conversely, a lower‐than‐normal CLLH SSR seems to result from the approximately opposite physical process during the years where the ISM is weak and EASM is strong over the CLLH. Given the fact that the correlation between the aerosol optical depth (AOD) and the CLLH SSR is relatively weak, the AOD variability may not be the main control on interannual variations of summer CLLH SSR.

Long-term variations of surface solar radiation in China from routine meteorological observations

Accurate observations of long-term surface solar radiation (SSR) are crucial for hydrological processes, agricultural production, and photovoltaic power generation. The main purpose of this study is to investigate the spatial-temporal variations and driving factors of SSR over mainland China. Firstly, ten selected models for estimating SSR were evaluated at 61 China Meteorological Administration (CMA) stations with SSR measurements. Then, the Yang's hybrid model (YHM) with the best model accuracy was used to construct a daily mean SSR dataset at 2474 CMA meteorological stations in China during 1961–2014. The results indicated that the annual mean SSR showed a fluctuating downward trend (−0.16 × 10−1 MJ m−2 year−1) during 1961–2014 under all sky condition. The annual mean SSR showed dimming trend over mainland China during 1961–1989 and 1990–2005, while the annual mean SSR experienced an increasing trend (0.02 × 10−1 MJ m−2 year−1) during 2005–2014 under all sky condition. Meanwhile, the annual mean SSR showed downward trend (−0.02 × 10−1 MJ m−2 year−1) during 1980–2014 under clear sky condition, while an increasing trend (0.06 × 10−1 MJ m−2 year−1) appeared under clear sky conditions from 2005 to 2014. The Qinghai-Tibet Plateau was always the area with the relatively higher SSR values, while the Sichuan Basin was generally the area with the relatively lower SSR values. Finally, the potential relationships between SSR and climate factors were analyzed. The result showed that the variation of annual mean SSR negatively correlates with the optical thickness of all cloud (TC) and the aerosol optical depth (AOD). The SSR had a significant positive correlation with sunshine duration (SD) under all sky conditions. The aerosol loading and SD were the primary factor of variation in clear sky SSR. The research will contribute to the studies related to climate change and land surface process.

Evidence for Clear‐Sky Dimming and Brightening in Central Europe

AbstractFor the explanation of the observed decadal variations in surface solar radiation (known as dimming and brightening), the relative importance of clouds and the cloud‐free atmosphere (particularly aerosols) is currently disputed. Here, we investigate this issue using daily data from the prominent long‐term observational radiation record at Potsdam, Germany, over the 71‐year period 1947–2017. We identify cloud‐free days based on synop cloud observations as well as on days with maximum atmospheric transmission. Irrespective of the cloud‐screening method, strong dimming and brightening tendencies in the atmospheric transmission are evident not only under all‐sky but also of similar magnitude under clear‐sky conditions, causing multidecadal variations in surface solar radiation on the order of 10 Wm−2. This points to the cloud‐free atmosphere as a main responsible for dimming and brightening in central Europe and suggests that these variations are anthropogenically forced rather than of natural origin, with aerosol pollutants as likely major drivers.

Solar Brightening/Dimming over China’s Mainland: Effects of Atmospheric Aerosols, Anthropogenic Emissions, and Meteorological Conditions

Surface solar radiation (SSR) is the main factor affecting the earth’s climate and environment and its variations and the reason for these variations are an important part of climate change research. In this research, we investigated the long-term variations of SSR during 1984–2016 and the quantitative influences of atmospheric aerosols, anthropogenic emissions, and meteorological conditions on SSR over China’s mainland. The results show the following: (1) The annual average SSR values had a decline trend at a rate of −0.371 Wm−2 yr−1 from 1984 to 2016 over China. (2) The aerosol optical depth (AOD) plays the main role in inducing variations in SSR over China, with r values of −0.75. Moreover, there are marked regional differences in the influence of anthropogenic emissions and meteorological conditions on SSR trends. (3) From a regional perspective, AOD is the main influencing factor on SSR in northeast China (NEC), Yunnan Plateau and surrounding regions (YPS), North China (NC), and Loess Plateau (LP), with r values of −0.65, −0.60, −0.89, and −0.50, respectively. However, the main driving factors for SSR in northwest China (NWC) are “in cloud optical thickness of all clouds” (TAUTOT) (−0.26) and black carbon (BC) anthropogenic emissions (−0.21). TAUTOT (−0.39) and total precipitable water vapor (TQV) (−0.29) are the main influencing factors of SSR in the middle-lower Yangtze Plain (MYP). The main factors that influence SSR in southern China (SC) are surface pressure (PS) (−0.66) and AOD (−0.43). This research provides insights in understanding the variations of SSR and its relationships with anthropogenic conditions and meteorological factors.

Effects of aerosols and water vapour on spatial-temporal variations of the clear-sky surface solar radiation in China

Clear-sky solar radiation is an important indicator describing the potential of solar energy. The aerosols and water vapour, apart from geometrical/astronomical ones, are the main factors resulting in the losses of the surface solar radiation (SSR) under clear sky conditions. This study uses satellite aerosol data, reanalysis water vapour data, and the Mesoscale Atmospheric Irradiance Code to create the clear-sky SSR dataset for China in 2001–2015. The aerosol direct radiative effect (ADRE) and water vapour radiative effect (WVRE) are calculated to study the clear-sky SSR losses due to aerosols and water vapour. The coefficient of determination (R2) of the observations and simulations is 0.944. The mean absolute error (MAE) and root mean square error (RMSE) are 6.67% and 9.00%, respectively. The strongest attenuation in clear-sky SSR due to aerosols occurs in April in most areas of China, while in June in North China and the Yangtze River Delta, water vapour most strongly attenuates the clear-sky SSR in July, and the monthly solar radiation losses due to water vapour are higher than those due to aerosols. The high aerosol and water vapour contents are the reasons why the clear-sky SSR in North China and the Yangtze River Delta in June are lower than those in May. From 2001 to 2015, the clear-sky trend with the greatest increase of up to 0.389 W m−2 per year (2.48% in 15 years) occurs over central Inner Mongolia, which is related to the reduction in dust. The increasing concentration of particulate matter in the atmosphere results in the most significant decreasing clear-sky trend in North China (−0.510 W m−2 year−1, 3.35% in 15 years). Generally, the ADRE variations are the main factor controlling the annual variations in clear-sky SSR.

A trend of surface solar radiation in Chiang Mai, Thailand

The solar radiation passing through the atmosphere to the earth surface has varied in both increasing and decreasing directions. The decreasing direction caused mainly by aerosols, which its properties can absorb and reflect solar radiation. The emission sources of aerosol are primarily from human activities. This study aims to delineate a trend of surface solar radiation in Chiang Mai by using data from 7 air quality monitoring stations, recording during 1995–2017 in urban and rural areas. According to the Mann Kendal Sen’s Slope analysis, the results show that surface solar radiation in Chiang Mai has presented the decreasing trends in 5 stations which located in urban areas while the other 2 stations located in rural areas have presented increasing trends. This could be basically explained that the difference and intensity of activities between urban and rural areas has affected the variation of surface solar radiation.

Clear-Sky Surface Solar Radiation and the Radiative Effect of Aerosol and Water Vapor Based on Simulations and Satellite Observations over Northern China

The distribution and trend of clear-sky surface solar radiation (SSR) and the quantitative effects of aerosol and water vapor are investigated in northern China during 2001–2015 using radiation simulations and satellite observations. Clear-sky SSR in northern China is high in summer and low in winter, which is dominated by astronomical factors and strongly modulated by the seasonal variations of radiative effects of aerosol (ARE) and water vapor (WVRE). The larger variation of WVRE than ARE indicates that water vapor plays a more important role in moderating the seasonal variation of clear-sky SSR. Clear-sky SSR shows an overall decreasing trend of –0.12 W/m2 per year, with decrease more strongly than –0.60 W/m2 per year in west-central Shandong and increase (about 0.40 W/m2) in south-central Inner Mongolia. The consistency of spatial distribution and high correlation between clear-sky SSR and ARE trend indicate that the clear-sky SSR trend is mainly determined by aerosol variation. Dust mass concentration decreases about 16% in south-central Inner Mongolia from 2001 to 2015, resulting in the increase in clear-sky SSR. In contrast, sulfate aerosol increases about 92% in west-central Shandong, leading to the decreasing trend of clear-sky SSR.

Satellite-based trends of solar radiation and cloud parameters in Europe

Abstract. Solar radiation is the main driver of the Earth's climate. Measuring solar radiation and analysing its interaction with clouds are essential for the understanding of the climate system. The EUMETSAT Satellite Application Facility on Climate Monitoring (CM SAF) generates satellite-based, high-quality climate data records, with a focus on the energy balance and water cycle. Here, multiple of these data records are analyzed in a common framework to assess the consistency in trends and spatio-temporal variability of surface solar radiation, top-of-atmosphere reflected solar radiation and cloud fraction. This multi-parameter analysis focuses on Europe and covers the time period from 1992 to 2015. A high correlation between these three variables has been found over Europe. An overall consistency of the climate data records reveals an increase of surface solar radiation and a decrease in top-of-atmosphere reflected radiation. In addition, those trends are confirmed by negative trends in cloud cover. This consistency documents the high quality and stability of the CM SAF climate data records, which are mostly derived independently from each other. The results of this study indicate that one of the main reasons for the positive trend in surface solar radiation since the 1990's is a decrease in cloud coverage even if an aerosol contribution cannot be completely ruled out.

Trends and Variability of Surface Solar Radiation in Europe Based On Surface‐ and Satellite‐Based Data Records

AbstractThe incoming solar radiation is the essential climate variable that determines the Earth's energy cycle and climate. As long‐term high‐quality surface measurements of solar radiation are rare, satellite data are used to derive more information on its spatial pattern and its temporal variability. Recently, the EUMETSAT Satellite Application on Climate Monitoring (CM SAF) has published two satellite‐based climate data records: Surface Solar Radiation Data Set‐Heliosat, Edition 2 (SARAH‐2), and Clouds and Radiation Data Set based on AVHRR (advanced very high resolution radiometer) Satellite Measurements, Edition 2 (CLARA‐A2). Both data records provide estimates of surface solar radiation. In this study, these new climate data records are compared to surface measurements in Europe during the period 1983–2015. SARAH‐2 and CLARA‐A2 show a high accuracy compared to ground‐based observations (mean absolute deviations of 6.9 and 7.3 W/m2, respectively) highlighting a good agreement considering the temporal behavior and the spatial distribution. The results show an overall brightening period since the 1980s onward (comprised between 1.9 and 2.4 W/m2/decade), with substantial decadal and spatial variability. The strongest brightening is found in eastern Europe in spring. An exception is found for northern and southern Europe, where the trends shown by the station data are not completely reproduced by satellite data, especially in summer in southern Europe. We conclude that the major part of the observed trends in surface solar radiation in Europe is caused by changes in clouds and that remaining differences between the satellite‐ and the station‐based data might be connected to changes in the direct aerosol effect and in snow cover.

An investigation of cloud base height in Chiang Mai

Clouds play very important role in the variation of surface solar radiation and rain formation. To understand this role, it is necessary to know the physical and geometrical of properties of cloud. However, clouds vary with location and time, which lead to a difficulty to obtain their properties. In this work, a ceilometer was installed at a station of the Royal Rainmaking and Agricultural Aviation Department in Chiang Mai (17.80° N, 98.43° E) in order to measure cloud base height. The cloud base height data from this instrument were compared with those obtained from LiDAR, a more sophisticated instrument installed at the same site. It was found that the cloud base height from both instruments was in reasonable agreement, with root mean square difference (RMSD) and mean bias difference (MBD) of 19.21% and 1.58%, respectively. Afterward, a six-month period (August, 2016-January, 2017) of data from the ceilometer was analyzed. The results show that mean cloud base height during this period is 1.5 km, meaning that most clouds are in the category of low-level cloud.