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3 pages, 173 KiB

Open AccessEditorial

Lower Atmosphere Meteorology

by M. Ángeles García and Isidro A. Pérez

Atmosphere 2019, 10(10), 609; https://doi.org/10.3390/atmos10100609 - 10 Oct 2019

Cited by 2 | Viewed by 2434

Abstract

The Atmosphere Special Issue “Lower Atmosphere Meteorology” comprises thirteen original papers dealing with different meteorological processes that occur in the layer of the atmosphere close to the surface and which can greatly affect living beings and materials [...] Full article

(This article belongs to the Special Issue Lower Atmosphere Meteorology)

Research

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13 pages, 2364 KiB

Open AccessArticle

Investigating the Effect of Different Meteorological Conditions on MAX-DOAS Observations of NO₂ and CHOCHO in Hefei, China

by Zeeshan Javed, Cheng Liu, Kalim Ullah, Wei Tan, Chengzhi Xing and Haoran Liu

Atmosphere 2019, 10(7), 353; https://doi.org/10.3390/atmos10070353 - 27 Jun 2019

Cited by 12 | Viewed by 3539

Abstract

In this work, a ground-based remote sensing instrument was used for observation of the trace gases NO₂ and CHOCHO in Hefei, China. Excessive development and rapid economic growth over the years have resulted in the compromising of air quality in this city, [...] Read more.

In this work, a ground-based remote sensing instrument was used for observation of the trace gases NO₂ and CHOCHO in Hefei, China. Excessive development and rapid economic growth over the years have resulted in the compromising of air quality in this city, with haze being the most prominent environmental problem. This is first study covering observation of CHOCHO in Hefei (31.783° N, 117.201° E). The observation period of this study, i.e., July 2018 to December 2018, is divided into three different categories: (1) clear days, (2) haze days, and (3) severe haze days. The quality of the differential optical absorption spectroscopy (DOAS) fit for both CHOCHO and NO₂ was low during severe haze days due to a reduced signal to noise ratio. NO₂ and CHOCHO showed positive correlations with PM2.5, producing R values of 0.95 and 0.98, respectively. NO₂ showed strong negative correlations with visibility and air temperature, obtaining R values of 0.97 and 0.98, respectively. CHOCHO also exhibited strong negative correlations with temperature and visibility, displaying R values of 0.83 and 0.91, respectively. The average concentration of NO₂, CHOCHO, and PM2.5 during haze days was larger compared to that of clear days. Diurnal variation of both CHOCHO and NO₂ showed a significant decreasing trend in the afternoons during clear days due to photolysis, while during haze days these two gases started to accumulate as their residence time increases in the absence of photolysis. There was no prominent weekly cycle for both trace gases. Full article

(This article belongs to the Special Issue Lower Atmosphere Meteorology)

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24 pages, 11943 KiB

Open AccessArticle

Analysis of Mountain Wave Effects on a Hard Landing Incident in Pico Aerodrome Using the AROME Model and Airborne Observations

by Jin Maruhashi, Pedro Serrão and Margarida Belo-Pereira

Atmosphere 2019, 10(7), 350; https://doi.org/10.3390/atmos10070350 - 26 Jun 2019

Cited by 11 | Viewed by 4527

Abstract

A hard landing incident in Pico Aerodrome (LPPI) involving an Airbus A320-200 aircraft is investigated using airborne observations and forecasts of the AROME (Applications of Research to Operations at Mesoscale) model. A second flight is also analyzed. The severity of the wind shear [...] Read more.

A hard landing incident in Pico Aerodrome (LPPI) involving an Airbus A320-200 aircraft is investigated using airborne observations and forecasts of the AROME (Applications of Research to Operations at Mesoscale) model. A second flight is also analyzed. The severity of the wind shear during both flights is quantified using the intensity factor “I” that is based on aerial data and recommended by ICAO (International Civil Aviation Organization). During Flight 1, 36% of the landing phase (below 2100 ft) occurred under “severe” wind shear conditions and 16% occurred under “strong” conditions. Upstream characteristics included southwest winds, stable stratification and a Froude number close to 1. According to the AROME model, these circumstances triggered the development of vertically propagating mountain waves, with maximum vertical velocities above 400 ft/min and exceeding 200 ft/min in the flight path. These conditions, together with the severe wind shear, may have caused the incident. During the second flight, a wake with lee vortices and reversed flow developed in the region of the flight path, which is consistent with a low upstream Froude number and/or with the flow regime diagram of previous studies. During the approach phase of this flight, “severe” wind shear conditions were absent, with “strong” ones occurring 4% of the time. It predominantly displayed “light” conditions during 68% of this phase. As a result of the comparison between “I” and the AROME turbulence indicators, preliminary thresholds are proposed for these indexes. Lastly, this study provides an objective verification of AROME wind forecasts, showing a good agreement with airborne observations for wind speeds above 10 kt, but a poor skill for weaker winds. Full article

(This article belongs to the Special Issue Lower Atmosphere Meteorology)

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14 pages, 3776 KiB

Open AccessArticle

Hurricane Boundary Layer Height Relative to Storm Motion from GPS Dropsonde Composites

by Yifang Ren, Jun A. Zhang, Stephen R. Guimond and Xiang Wang

Atmosphere 2019, 10(6), 339; https://doi.org/10.3390/atmos10060339 - 21 Jun 2019

Cited by 15 | Viewed by 4617

Abstract

This study investigates the asymmetric distribution of hurricane boundary layer height scales in a storm-motion-relative framework using global positioning system (GPS) dropsonde observations. Data from a total of 1916 dropsondes collected within four times the radius of maximum wind speed of 37 named [...] Read more.

This study investigates the asymmetric distribution of hurricane boundary layer height scales in a storm-motion-relative framework using global positioning system (GPS) dropsonde observations. Data from a total of 1916 dropsondes collected within four times the radius of maximum wind speed of 37 named hurricanes over the Atlantic basin from 1998 to 2015 are analyzed in the composite framework. Motion-relative quadrant mean composite analyses show that both the kinematic and thermodynamic boundary layer height scales tend to increase with increasing radius in all four motion-relative quadrants. It is also found that the thermodynamic mixed layer depth and height of maximum tangential wind speed are within the inflow layer in all motion-relative quadrants. The inflow layer depth and height of the maximum tangential wind are both found to be deeper in the two front quadrants, and they are largest in the right-front quadrant. The difference in the thermodynamic mixed layer depth between the front and back quadrants is smaller than that in the kinematic boundary layer height. The thermodynamic mixed layer is shallowest in the right-rear quadrant, which may be due to the cold wake phenomena. The boundary layer height derived using the critical Richardson number (

R_{i c}

) method shows a similar front-back asymmetry as the kinematic boundary layer height. Full article

(This article belongs to the Special Issue Lower Atmosphere Meteorology)

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16 pages, 6486 KiB

Open AccessArticle

Diurnal Variations of Different Cloud Types and the Relationship between the Diurnal Variations of Clouds and Precipitation in Central and East China

by Cuicui Gao, Yunying Li and Haowei Chen

Atmosphere 2019, 10(6), 304; https://doi.org/10.3390/atmos10060304 - 3 Jun 2019

Cited by 12 | Viewed by 5310

Abstract

In this paper, the diurnal variations of various clouds are analyzed using hourly cloud observations at weather stations in China from 1985 to 2011. In combination with merged hourly precipitation data, the relationship between the diurnal variations of clouds and precipitation in the [...] Read more.

In this paper, the diurnal variations of various clouds are analyzed using hourly cloud observations at weather stations in China from 1985 to 2011. In combination with merged hourly precipitation data, the relationship between the diurnal variations of clouds and precipitation in the summers from 2008 to 2011 are studied. The results show that the occurrence frequencies of total cloud and various cloud types exhibit significant diurnal variations. The diurnal variations of the occurrence frequencies of altocumulus and stratocumulus show a bimodal pattern, with peaks appearing in the early morning and late afternoon. The early morning peaks of altocumulus and stratocumulus appear earlier in the summer than in the other seasons, while the late afternoon maxima show an opposite trend. The occurrence frequency of nimbostratus peaks in the morning between 07 and 12 LST (local solar time), and the peak value lags 2 to 3 h from west to east along the Yangtze River valley; meanwhile, the diurnal variation shows no clear differences caused by changes in the latitude or seasons. Cumulus shows an afternoon (14 LST) maximum, while cumulonimbus peaks in the late afternoon during 16–20 LST, and both of them present a great diurnal range. Cirrus usually reaches its peak at 17–18 LST, and it differs by 1 to 2 h with a change in the latitude. The results of the study first show that the diurnal variations of precipitation among different regions are dominated by different clouds. The upper reaches of the Yangtze River valley present a midnight precipitation maximum that is mainly dominated by cumulonimbus. For the middle reaches of the Yangtze River valley impacted by nimbostratus, the precipitation peaks in the early morning. In South and Northeast China, the precipitation peaks in the afternoon and is determined by the diurnal variations of convective clouds. In the region between the Yangtze River valley and Yellow River valley, the precipitation peaks in the early morning and afternoon; the early morning peak is mainly determined by stratiform clouds, while the afternoon peak is closely related to convective clouds. Full article

(This article belongs to the Special Issue Lower Atmosphere Meteorology)

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17 pages, 6845 KiB

Open AccessArticle

Impacts of Green Vegetation Fraction Derivation Methods on Regional Climate Simulations

by Jose Manuel Jiménez-Gutiérrez, Francisco Valero, Sonia Jerez and Juan Pedro Montávez

Atmosphere 2019, 10(5), 281; https://doi.org/10.3390/atmos10050281 - 21 May 2019

Cited by 3 | Viewed by 3492

Abstract

The representation of vegetation in land surface models (LSM) is crucial for modeling atmospheric processes in regional climate models (RCMs). Vegetation is characterized by the green fractional vegetation cover (FVC) and/or the leaf area index (LAI) that are obtained from nearest difference vegetation [...] Read more.

The representation of vegetation in land surface models (LSM) is crucial for modeling atmospheric processes in regional climate models (RCMs). Vegetation is characterized by the green fractional vegetation cover (FVC) and/or the leaf area index (LAI) that are obtained from nearest difference vegetation index (NDVI) data. Most regional climate models use a constant FVC for each month and grid cell. In this work, three FVC datasets have been constructed using three methods: ZENG, WETZEL and GUTMAN. These datasets have been implemented in a RCM to explore, through sensitivity experiments over the Iberian Peninsula (IP), the effects of the differences among the FVC data-sets on the near surface temperature (T2m). Firstly, we noted that the selection of the NDVI database is of crucial importance, because there are important bias in mean and variability among them. The comparison between the three methods extracted from the same NDVI database, the global inventory modeling and mapping studies (GIMMS), reveals important differences reaching up to 12% in spatial average and and 35% locally. Such differences depend on the FVC magnitude and type of biome. The methods that use the frequency distribution of NDVI (ZENG and GUTMAN) are more similar, and the differences mainly depends on the land type. The comparison of the RCM experiments exhibits a not negligible effect of the FVC uncertainty on the monthly T2m values. Differences of 30% in FVC can produce bias of 1

^{\circ}

C in monthly T2m, although they depend on the time of the year. Therefore, the selection of a certain FVC dataset will introduce bias in T2m and will affect the annual cycle. On the other hand, fixing a FVC database, the use of synchronized FVC instead of climatological values produces differences up to 1

^{\circ}

C, that will modify the T2m interannual variability. Full article

(This article belongs to the Special Issue Lower Atmosphere Meteorology)

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18 pages, 2206 KiB

Open AccessArticle

Spatiotemporal Change of Plum Rains in the Yangtze River Delta and Its Relation with EASM, ENSO, and PDO During the Period of 1960–2012

by Nina Zhu, Jianhua Xu, Kaiming Li, Yang Luo, Dongyang Yang and Cheng Zhou

Atmosphere 2019, 10(5), 258; https://doi.org/10.3390/atmos10050258 - 9 May 2019

Cited by 9 | Viewed by 3434

Abstract

The Plum Rains process is a complex process, and its spatiotemporal variations and influencing factors on different time scales still need further study. Based on a dataset on the Plum Rains in the Yangtze River Delta, from 33 meteorological stations during the period [...] Read more.

The Plum Rains process is a complex process, and its spatiotemporal variations and influencing factors on different time scales still need further study. Based on a dataset on the Plum Rains in the Yangtze River Delta, from 33 meteorological stations during the period of 1960 to 2012, we investigated the spatiotemporal variations of Plum Rains and their relation with the East Asian Summer Monsoon (EASM), the El Niño-Southern Oscillation (ENSO), and the Pacific Decadal Oscillation (PDO) using an integrated approach that combines ensemble empirical mode decomposition (EEMD), empirical orthogonal function (EOF), and correlation analysis. The main conclusions were as follows: (1) the plum rainfall (i.e., the rainfall during the period of Plum Rains) showed a trend of increasing first and then decreasing, and it had a three-year and six-year cycle on the inter-annual scale and a 13-year and 33-year cycle on the inter-decadal scale. The effect of the onset and termination of Plum Rains and the daily intensity of plum rainfall on plum rainfall on the inter-annual scale was greater than the inter-decadal scale, (2) the EOF analysis of plum rainfall revealed a dominant basin-wide in-phase pattern (EOF1) and a north-south out-of-phase pattern (EOF2), and (3) ENSO and EASM were the main influencing factors in the three-year and six-year periods, respectively. Full article

(This article belongs to the Special Issue Lower Atmosphere Meteorology)

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12 pages, 3202 KiB

Open AccessArticle

Air Mass Trajectories to Estimate the “Most Likely” Areas to Be Affected by the Release of Hazardous Materials in the Atmosphere—Feasibility Study

by Miguel Ángel Hernández-Ceballos and Luca De Felice

Atmosphere 2019, 10(5), 253; https://doi.org/10.3390/atmos10050253 - 8 May 2019

Cited by 6 | Viewed by 4267

Abstract

Countries continuously review and improve their Emergency Preparedness and Response (EP&R) arrangements and capabilities to take agile and rapid actions with the intent of minimizing health, environmental and economic impacts of potential harmful releases into the atmosphere. One of the specific topics within [...] Read more.

Countries continuously review and improve their Emergency Preparedness and Response (EP&R) arrangements and capabilities to take agile and rapid actions with the intent of minimizing health, environmental and economic impacts of potential harmful releases into the atmosphere. One of the specific topics within the EP&R field is the estimation of the areas that might be affected. A proposal is presented to estimate the spatial distribution of the released material. The methodology combines the computation of air mass trajectories and the elaboration of density maps from the corresponding end-point positions. To this purpose, density maps are created in a three-way procedure; first, forward trajectories are calculated from a certain location and for a long period of time, e.g., a decade; second, the selected end-point positions are aggregated in a density field by applying the kernel density estimation method, and then the density field is visualized. The final product reports the areas with the longest residence time of air masses, and hence, the areas “most likely” to be affected and where the deposit may be substantial. The usefulness of this method is evaluated taking as reference a ten-year period (2007–2016) and against two different radioactive release scenarios, such as the Chernobyl accident and the Algeciras release. While far from being fully comprehensive, as only meteorological data are used, the performance of this method is reasonably efficient, and hence, it is a desirable alternative to estimating those areas potentially affected by a substantial deposit following the releases of a harmful material in the atmosphere. Full article

(This article belongs to the Special Issue Lower Atmosphere Meteorology)

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15 pages, 3171 KiB

Open AccessArticle

Suitable Pattern of the Natural Environment of Human Settlements in the Lower Reaches of the Yangtze River

by Fan Song, Xiaohua Yang and Feifei Wu

Atmosphere 2019, 10(4), 200; https://doi.org/10.3390/atmos10040200 - 12 Apr 2019

Cited by 17 | Viewed by 3764

Abstract

The human settlement environment is the object on which human survival depends. In this study, six single factor suitability models and a comprehensive index model of the human settlement natural environment were established. The six single factor models included topography, hydrology, vegetation, soil, [...] Read more.

The human settlement environment is the object on which human survival depends. In this study, six single factor suitability models and a comprehensive index model of the human settlement natural environment were established. The six single factor models included topography, hydrology, vegetation, soil, temperature and humidity, and land surface temperature. This study took 1 km × 1 km as the pixel size and relied on the ArcGIS platform to systematically and quantitatively evaluate the human settlement environment of the lower reaches of the Yangtze river. The results show that: (1) From the evaluation results of single natural elements, the topography of the study area is relatively flat, with a small number of hydraulic erosion areas. Besides, there are significant differences between the north and the south in temperature and humidity, hydrology, vegetation, and land surface temperature. (2) In 2015, the most suitable areas of human settlement environment were mainly distributed in the plains along the Yangtze river, the plain of northern Zhejiang, and the Poyang plain. The most unsuitable areas are mainly distributed in mountainous areas, such as the mountain area of southern Zhejiang and Dabie mountain area. Topography and vegetation are the dominant factors for classification. (3) From the perspective of space, the score of the human settlement natural environment in Shanghai is above the average, and the best among the other provinces is Jiangsu province, while Zhejiang, Jiangxi, and Anhui provinces have little difference. From the perspective of time, the overall level of the suitability in the lower reaches of the Yangtze river has been improved from 2005 to 2015, mainly due to the influence of temperature and humidity index and water resource index. Full article

(This article belongs to the Special Issue Lower Atmosphere Meteorology)

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21 pages, 3300 KiB

Open AccessArticle

Anthropogenic CH₄ Emissions in the Yangtze River Delta Based on A “Top-Down” Method

by Wenjing Huang, Wei Xiao, Mi Zhang, Wei Wang, Jingzheng Xu, Yongbo Hu, Cheng Hu, Shoudong Liu and Xuhui Lee

Atmosphere 2019, 10(4), 185; https://doi.org/10.3390/atmos10040185 - 5 Apr 2019

Cited by 9 | Viewed by 5004

Abstract

There remains significant uncertainty in the estimation of anthropogenic CH₄ emissions at local and regional scales. We used atmospheric CH₄ and CO₂ concentration data to constrain the anthropogenic CH₄ emission in the Yangtze River Delta one of the most [...] Read more.

There remains significant uncertainty in the estimation of anthropogenic CH₄ emissions at local and regional scales. We used atmospheric CH₄ and CO₂ concentration data to constrain the anthropogenic CH₄ emission in the Yangtze River Delta one of the most populated and economically important regions in China. The observation of atmospheric CH₄ and CO₂ concentration was carried out from May 2012 to April 2017 at a rural site. A tracer correlation method was used to estimate the anthropogenic CH₄ emission in this region, and compared this “top-down” estimate with that obtained with the IPCC inventory method. The annual growth rates of the atmospheric CO₂ and CH₄ mole fractions are 2.5 ± 0.7 ppm year⁻¹ and 9.5 ± 4.7 ppb year⁻¹, respectively, which are 9% and 53% higher than the values obtained at Waliguan (WLG) station. The average annual anthropogenic CH₄ emission is 4.37 (± 0.61) × 10⁹ kg in the YRD (excluding rice cultivation). This “top-down” estimate is 20–70% greater than the estimate based on the IPCC method. We suggest that possible sources for the discrepancy include low biases in the IPCC calculation of emission from landfills, ruminants and the transport sector. Full article

(This article belongs to the Special Issue Lower Atmosphere Meteorology)

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15 pages, 7222 KiB

Open AccessArticle

Seasonal and Interannual Variation Characteristics of Low-Cloud Fraction in Different North Pacific Regions

by Qian Wang, Haiming Xu, Leying Zhang and Jiechun Deng

Atmosphere 2019, 10(3), 126; https://doi.org/10.3390/atmos10030126 - 7 Mar 2019

Cited by 3 | Viewed by 4063

Abstract

In this study, we use the long-term satellite data to investigate seasonal and interannual variation of low-cloud fraction (LCF) and the associated controlling factors over the eastern and western North Pacific. On the seasonal time scale, the enhanced LCF over the eastern North [...] Read more.

In this study, we use the long-term satellite data to investigate seasonal and interannual variation of low-cloud fraction (LCF) and the associated controlling factors over the eastern and western North Pacific. On the seasonal time scale, the enhanced LCF over the eastern North Pacific in summer is actively coupled with strong estimated inversion strength (EIS) and 700-hPa relative humidity, and the LCF over the western North Pacific in winter is large and mainly caused by increased sensible heat flux and tropospheric low-level cold advection. On the interannual time scale, the increased LCF over the eastern North Pacific in summer is associated with increased EIS and decreased sea surface temperatures, in which the El Niño plays an important role; the enhanced LCF over the western North Pacific in spring and winter has a positive correlation with enhanced sensible heat flux (SHF) and tropospheric low-level cold advection, which can be partly explained by the subpolar frontal zone (SPFZ) intensity. Full article

(This article belongs to the Special Issue Lower Atmosphere Meteorology)

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11 pages, 3217 KiB

Open AccessArticle

Diurnal Variations in Surface Wind over the Tibetan Plateau

by Yufei Zhao, Jianping Li, Qiang Zhang, Xiaowei Jiang and Aixia Feng

Atmosphere 2019, 10(3), 112; https://doi.org/10.3390/atmos10030112 - 2 Mar 2019

Cited by 3 | Viewed by 4724

Abstract

This study uses hourly surface wind direction and wind speed observations from 53 meteorological stations on the Tibetan Plateau (TP) (70–105° E, 25–45° N) between 1995 and 2017 to investigate diurnal variations in the surface wind. The results show large diurnal variations in [...] Read more.

This study uses hourly surface wind direction and wind speed observations from 53 meteorological stations on the Tibetan Plateau (TP) (70–105° E, 25–45° N) between 1995 and 2017 to investigate diurnal variations in the surface wind. The results show large diurnal variations in surface wind on the TP. The minimum wind speed occurs in the morning and the maximum in the afternoon. In all four seasons, the prevailing meridional wind is a southerly, and this is typically evident for more than two-thirds of each day. However, in the mornings during December–February and September–November, this southerly wind is replaced by a northerly, but remains southerly in the afternoon. The TP shows remarkable regional characteristics with respect to diurnal variations in wind speed. In the eastern region, the minimum and maximum daily wind speeds occur about 1 h later than in the west. Among the 53 meteorological stations, 79% observed that it took less time for the minimum speed to rise to the maximum speed than for the maximum to drop to the minimum. The blocking effect of the high surrounding terrain causes the diurnal variations seen in the surface winds at the three stations in the Qaidam Basin to differ significantly from those observed at the other stations elsewhere on the plateau. These Qaidam Basin stations recorded their maximum wind speeds around noon, with the minimum at dusk, which is around 1900 LST. The EOF1 (EOF = empirical orthogonal function) of the hourly wind speed on the TP indicates the key daily circulation feature of the region; i.e., the wind speed is high in the afternoon and low in the morning. The EOF2 reflects the regional differences in the diurnal variations of wind speed on the TP; i.e., the eastern region reaches the daily maximum and minimum wind speeds slightly later than the western region. Full article

(This article belongs to the Special Issue Lower Atmosphere Meteorology)

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14 pages, 5008 KiB

Open AccessArticle

Sub-Mode Aerosol Volume Size Distribution and Complex Refractive Index from the Three-Year Ground-Based Measurements in Chengdu China

by Chi Zhang, Ying Zhang, Zhengqiang Li, Yongqian Wang, Hua Xu, Kaitao Li, Donghui Li, Yisong Xie and Yang Zhang

Atmosphere 2019, 10(2), 46; https://doi.org/10.3390/atmos10020046 - 26 Jan 2019

Cited by 5 | Viewed by 3891

Abstract

Chengdu is a typical basin city of Southwest China with rare observations of remote sensing measurements. To assess the climate change and establish a region aerosol model, a deeper understanding of the separated volume size distribution (VSD) and complex refractive index (CRI) is [...] Read more.

Chengdu is a typical basin city of Southwest China with rare observations of remote sensing measurements. To assess the climate change and establish a region aerosol model, a deeper understanding of the separated volume size distribution (VSD) and complex refractive index (CRI) is required. In this study, we employed the sub-mode VSD and CRI in Chengdu based on the three years observation data to investigate the sub-mode characteristics and climate effects. The annual average fraction of the fine-mode aerosol optical depth (AOD_f) is 92%, which has the same monthly tendency as the total AOD. But the coarse-mode aerosol optical depth (AOD_c) has little variation in different months. There are four distinguishing modes of VSD in Chengdu; the median radii are 0.17 μm ± 0.05, 0.31 μm ± 0.12, 1.62 μm ± 0.45, 3.25 μm ± 0.99, respectively. The multi-year average and seasonal variations of fine- and coarse-mode VSD and CRI are also analyzed to characterize aerosols over this region. The fine-mode single scattering albedos (SSAs) are higher than the coarse-mode ones, which suggests that the coarse-mode aerosols have a stronger absorbing effect on solar light than the small-size aerosol particles in Chengdu. Full article

(This article belongs to the Special Issue Lower Atmosphere Meteorology)

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15 pages, 3871 KiB

Open AccessArticle

Summertime Urban Mixing Layer Height over Sofia, Bulgaria

by Ventsislav Danchovski

Atmosphere 2019, 10(1), 36; https://doi.org/10.3390/atmos10010036 - 17 Jan 2019

Cited by 13 | Viewed by 4803

Abstract

Mixing layer height (MLH) is a crucial parameter for air quality modelling that is still not routinely measured. Common methods for MLH determination use atmospheric profiles recorded by radiosonde but this process suffers from coarse temporal resolution since the balloon is usually launched [...] Read more.

Mixing layer height (MLH) is a crucial parameter for air quality modelling that is still not routinely measured. Common methods for MLH determination use atmospheric profiles recorded by radiosonde but this process suffers from coarse temporal resolution since the balloon is usually launched only twice a day. Recently, cheap ceilometers are gaining popularity in the retrieval of MLH diurnal evolution based on aerosol profiles. This study presents a comparison between proprietary (Jenoptik) and freely available (STRAT) algorithms to retrieve MLH diurnal cycle over an urban area. The comparison was conducted in the summer season when MLH is above the full overlapping height of the ceilometer in order to minimize negative impact of the biaxial LiDAR’s drawback. Moreover, fogs or very low clouds which can deteriorate the ceilometer retrieval accuracy are very unlikely to be present in summer. The MLHs determined from the ceilometer were verified against those measured from the radiosonde, which were estimated using the parcel, lapse rate, and Richardson methods (the Richardson method was used as a reference in this study). We found that the STRAT and Jenoptik methods gave lower MLH values than radiosonde with an underestimation of about 150 m and 650 m, respectively. Additionally, STRAT showed some potential in tracking the MLH diurnal evolution, especially during the day. A daily MLH maximum of about 2000 m was found in the late afternoon (18–19 LT). The Jenoptik algorithm showed comparable results to the STRAT algorithm during the night (although both methods sometimes misleadingly reported residual or advected layers as the mixing layer (ML)). During the morning transition the Jenoptik algorithm outperformed STRAT, which suffers from abrupt changes in MLH due to integrated layer attribution. However, daytime performance of Jenoptik was worse, especially in the afternoon when the algorithm often cannot estimate any MLH (in the period 13–16 LT the method reports MLHs in only 15–30% of all cases). This makes day-to-day tracing of MLH diurnal evolution virtually impracticable. This problem is possibly due to its early version (JO-CloVis 8.80, 2009) and issues with real-time processing of a single profile combined with the low signal-to-noise ratio of the ceilometer. Both LiDAR-based algorithms have trouble in the evening transition since they rely on aerosol signature which is more affected by the mixing processes in the past hours than the current turbulent mixing. Full article

(This article belongs to the Special Issue Lower Atmosphere Meteorology)

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