scholarly journals Investigating long-term variations in cloud base height over Sofia, Bulgaria 

2021 ◽  
Author(s):  
Viktor Levi ◽  
Evgeni Vladimirov ◽  
Ventsislav Danchovski
Keyword(s):  
Traffic Safety ◽  
Climate Models ◽  
Global Radiation ◽  
Cloud Base ◽  
Advantages And Disadvantages ◽  
Climate Forecasting ◽  
Spatial Coverage ◽  
Weather And Climate ◽  
Surface Measurements ◽  
Cloud Base Height

<p> </p><p>Clouds have a key role in weather and climate forecasting due to their effect on global radiation and water budget. Clouds change the radiation energy in the Earth-atmosphere system by reducing both incoming and outgoing parts, depending on their macro- and microphysical characteristics such as cloud base height (CBH), optical properties etc. These clouds properties are generally related to cloud types, so the effects in weather and climate caused by various cloud types differ greatly. It is known that high clouds cause the earth's surface to heat up, while low clouds cause cooling. Obviously, cloud radiation forcing is an important source of uncertainty in the numerical weather and climate models, so the registered and expected changes in the properties of clouds due to a warming climate need in-depth studies. But cloud base height is not only important for weather and climate forecasting, but also for airplane traffic safety.  Nowadays, retrieving the CBH is mainly based on satellite and ground-based observations. Satellite-borne instruments provide tempting spatial coverage but uncertainty in CBH estimation should be considered. In contrast, many ground-based observations of the CBH are characterized by higher accuracy. Nowadays, ceilometers - lidars specifically designed to detect CBH, that operate continuously and unattended, providing high vertical and time-resolution data, are reference instrument in CBH measurement. In addition, rawinsondes provide in-situ measurements of temperature, humidity, and pressure, so that the CBH can be evaluated by the lifting condensation level or by threshold value in relative humidity. In areas where only surface measurements are available, a simple adiabatic model of a rising air parcel can be applied in the CBH assessment. In this work, based on ceilometer, rawinsonde and surface measurements, the characteristics of CBH over Sofia, Bulgaria are studied in detail. We start with an intercomparison between CBHs obtained from three types of ground-based observations, considering the individual advantages and disadvantages of the methods by using ceilometer as reference. Finally, the daily, seasonal and interannual variability of CBH over Sofia are interpreted.</p>

scholarly journals Cloud Base Height Estimation from ISCCP Cloud-Type Classification Applied to A-Train Data

2017 ◽  
Vol 2017 ◽  
pp. 1-14 ◽  
Author(s):  
Yao Liang ◽  
Xuejin Sun ◽  
Steven D. Miller ◽  
Haoran Li ◽  
Yongbo Zhou ◽  
...  
Keyword(s):  
Global Radiation ◽  
Estimation Method ◽  
Separation Distance ◽  
Cloud Base ◽  
Radiation Balance ◽  
Cloud Type ◽  
Active Sensors ◽  
Combined Algorithm ◽  
Type Classification ◽  
Cloud Base Height

Cloud base height (CBH) is an important cloud macro parameter that plays a key role in global radiation balance and aviation flight. Building on a previous algorithm, CBH is estimated by combining measurements from CloudSat/CALIPSO and MODIS based on the International Satellite Cloud Climatology Project (ISCCP) cloud-type classification and a weighted distance algorithm. Additional constraints on cloud water path (CWP) and cloud top height (CTH) are introduced. The combined algorithm takes advantage of active and passive remote sensing to effectively estimate CBH in a wide-swath imagery where the cloud vertical structure details are known only along the curtain slice of the nonscanning active sensors. Comparisons between the estimated and observed CBHs show high correlation. The coefficient of association (R2) is 0.8602 with separation distance between donor and recipient points in the range of 0 to 100 km and falls off to 0.5856 when the separation distance increases to the range of 401 to 600 km. Also, differences are mainly within 1 km when separation distance ranges from 0 km to 600 km. The CBH estimation method was applied to the 3D cloud structure of Tropical CycloneBill, and the method is further assessed by comparing CTH estimated by the algorithm with the MODIS CTH product.

scholarly journals Clouds over Hyytiälä, Finland: an algorithm to classify clouds based on solar radiation and cloud base height measurements

2020 ◽  
Author(s):  
Ilona Ylivinkka ◽  
Santeri Kaupinmäki ◽  
Meri Virman ◽  
Maija Peltola ◽  
Ditte Taipale ◽  
...  
Keyword(s):  
Solar Radiation ◽  
Global Radiation ◽  
Simple Algorithm ◽  
Cloud Base ◽  
Aerosol Formation ◽  
Detection Range ◽  
Clear Sky ◽  
Overall Performance ◽  
Sky Conditions ◽  
Cloud Base Height

Abstract. We developed a simple algorithm to classify clouds based on global radiation and cloud base height measured by pyranometer and ceilometer, respectively. We separated clouds into seven different classes (stratus, stratocumulus, cumulus, nimbostratus, altocumulus+altostratus, cirrus+cirrocumulus+cirrostratus and clear sky+cirrus). We also included classes for cumulus and cirrus clouds causing global radiation enhancement, and classified multilayered clouds, when captured by the ceilometer, based on their height and characteristics (transparency, patchiness and uniformity). The overall performance of the algorithm was nearly 70 % when compared with classification by an observer using total sky images. The performance was best for clouds having well-distinguishable effects on solar radiation: nimbostratus clouds were classified correctly in 100 % of the cases. The worst performance corresponds to cirriform clouds (50 %). Although the overall performance of the algorithm was good, it is likely to miss the occurrence of high and multilayered clouds. This is due to the technical limits of the instrumentation: the vertical detection range of the ceilometer and occultation of the laser pulse by the lowest cloud layer. We examined the use of brightness parameter, which is defined as a ratio between measured global radiation and modeled radiation at the top of the atmosphere, as an indicator of clear sky conditions. Our results show that cumulus, altocumulus, altostratus and cirriform clouds can be present when the parameter indicates clear sky conditions. Those conditions have previously been associated with enhanced aerosol formation under clear sky. This is an important finding especially in case of low clouds coupled to the surface which can influence aerosol population via aerosol-cloud interactions. Overall, caution is required when the parameter is used in the analysis of processes affected by partitioning of radiation by clouds.

scholarly journals Features of the Cloud Base Height and Determining the Threshold of Relative Humidity over Southeast China

2019 ◽  
Vol 11 (24) ◽  
pp. 2900 ◽  
Author(s):  
Yuzhi Liu ◽  
Yuhan Tang ◽  
Shan Hua ◽  
Run Luo ◽  
Qingzhe Zhu
Keyword(s):  
Relative Humidity ◽  
Hydrological Cycle ◽  
Critical Role ◽  
Global Radiation ◽  
Radiation Budget ◽  
Cloud Base ◽  
Accurate Information ◽  
Southeast China ◽  
Environmental Relative Humidity ◽  
Cloud Base Height

Clouds play a critical role in adjusting the global radiation budget and hydrological cycle; however, obtaining accurate information on the cloud base height (CBH) is still challenging. In this study, based on Lidar and aircraft soundings, we investigated the features of the CBH and determined the thresholds of the environmental relative humidity (RH) corresponding to the observed CBHs over Southeast China from October 2017 to September 2018. During the observational period, the CBHs detected by Lidar/aircraft were commonly higher in cold months and lower in warm months; in the latter, 75.91% of the CBHs were below 2000 m. Overall, the RHs at the cloud base were mainly distributed between 70 and 90% for the clouds lower than 1000 m, in which the most concentrated RH was approximately 80%. In addition, for the clouds with a cloud base higher than 1000 m, the RH thresholds decreased dramatically with increasing CBH, where the RH thresholds at cloud bases higher than 2000 m could be lower than 60%. On average, the RH thresholds for determining the CBHs were the highest (72.39%) and lowest (63.56%) in the summer and winter, respectively, over Southeast China. Therefore, to determine the CBH, a specific threshold of RH is needed. Although the time period covered by the collected CBH data from Lidar/aircraft is short, the above analyses can provide some verification and evidence for using the RH threshold to determine the CBH.

scholarly journals Large-Scale Synoptic Systems and Fog During the C-FOG Field Experiment

2021 ◽  
Author(s):  
Clive E. Dorman ◽  
Sebastian W. Hoch ◽  
Ismail Gultepe ◽  
Qing Wang ◽  
Ryan T. Yamaguchi ◽  
...  
Keyword(s):  
Large Scale ◽  
Longwave Radiation ◽  
Meteorological Conditions ◽  
Cloud Base ◽  
Atlantic Canada ◽  
The North ◽  
Coastal Fog ◽  
Surface Measurements ◽  
Avalon Peninsula ◽  
Cloud Base Height

AbstractThe goal of this work is to summarize synoptic meteorological conditions during the Coastal Fog (C-FOG) field project that took place onshore and offshore of the Avalon Peninsula, Newfoundland, from 25 August until 8 October 2018. Visibility was measured at three locations at the Ferryland supersite that are about 1 km from each other, and at two additional sites 66 and 76 km to the north. Supporting meteorological measurements included surface winds, air temperature, humidity, pressure, radiation, cloud-base height, and atmospheric thermodynamic profiles from radiosonde soundings. Statistics are presented for surface measurements during fog events including turbulence kinetic energy, net longwave radiation, visibility, and precipitation. Eleven fog events are observed at Ferryland. Each significant fog event is related to a large-scale cyclonic system. The longest fog event is due to interaction of a northern deep low and a tropical cyclone. Fog occurrence is also examined across Atlantic Canada by including Sable Island, Yarmouth, Halifax, and Sydney. It is concluded that at Ferryland, all significant fog events occur under a cyclonic system while at Sable Island all significant fog events occur under both cyclonic and anticyclonic systems. The fog-formation mechanism involves cloud lowering and stratus broadening or only stratus broadening for the cyclonic systems while for the anticyclonic systems it is stratus broadening or radiation. Although widely cited as the main cause of fog in Atlantic Canada, advection fog is not found to be the primary or sole fog type in the events examined.

scholarly journals A Study of the Characteristics of Vertical Cloud Base Height Distribution over Eastern China

Atmosphere ◽  
2019 ◽  
Vol 10 (6) ◽  
pp. 307 ◽  
Author(s):  
Jiwei Xu ◽  
Dong Liu ◽  
Zhenzhu Wang ◽  
Decheng Wu ◽  
Siqi Yu ◽  
...  
Keyword(s):  
Climate Models ◽  
Eastern China ◽  
Cloud Base ◽  
Satellite Measurement ◽  
Height Distribution ◽  
Weather System ◽  
The Difference ◽  
Ground Based Lidar ◽  
Cloud Base Height ◽  
Good Agreement

Cloud is an important factor that affects weather and climate, and the vertical distribution of cloud determines its role in the atmospheric radiation transfer process. In this paper, the characteristics of different cloud types and their vertical cloud base height distributions over Eastern China are investigated with a four-year 2B-CLDCLASS-LIDAR product. The intercomparison of cloud base height distribution from ground-based lidar, CloudSat and CALIPSO measurements was studied with observations over the Hefei and Jinhua areas. The 2B-CLDCLASS-LIDAR product has the potential to uncover geographical and seasonal changes in cloud base height distribution over the Hefei area and Jinhua area, which may be beneficial for local climate models, although the CPR on CloudSat suffers from surface clutter or blind-zones. The results show that for non-precipitation cloud over the defined region (Eastern China), the occurrence frequencies of altocumulus, stratocumulus, and cirrus clouds are 29.4%, 21.0%, and 18.9%, respectively. The vertical occurrence frequencies of their cloud base heights are 0.5–8.5 km, below 3.5 km, and 5.5–17.0 km. The precipitation clouds are dominated by nimbostratus (48.4%), cumulus (17.9%), and deep convective clouds (24.2%), and their cloud base heights are all below 3.0 km. The cloud base height distributions have large differences below 3 km between the satellite measurement and ground-based measurement over Hefei site. Between the Hefei site and Jinhua site, the difference in cloud base height distribution measured by ground-based lidar is in good agreement with that measured by satellite over their matched grid boxes. Over the Hefei site, the vertical occurrence frequencies of cloud base height measured by ground-based lidar are higher than the satellite measurement within 0–0.5 km during all the seasons. It is suggested that more cloudy days may result from the sufficient water vapor environment in Hefei. In summer, the occurrence frequency of the cloud base height distribution at a height of 0–2.0 km is lower than other seasons over Jinhua city, which may be associated with the local weather system. Over the Jinhua site, the difference in seasonal cloud base height distribution based on satellite is in good agreement with that based on ground-based lidar. However, it does not appear over Hefei site. Thus, a multi-platform observation of cloud base height seems to be one of the essential ways for improvement in the observation of cloud macroscopic properties.

scholarly journals Clouds over Hyytiälä, Finland: an algorithm to classify clouds based on solar radiation and cloud base height measurements

2020 ◽  
Vol 13 (10) ◽  
pp. 5595-5619
Author(s):  
Ilona Ylivinkka ◽  
Santeri Kaupinmäki ◽  
Meri Virman ◽  
Maija Peltola ◽  
Ditte Taipale ◽  
...  
Keyword(s):  
Solar Radiation ◽  
Global Radiation ◽  
Cloud Base ◽  
Aerosol Formation ◽  
Clearness Index ◽  
Detection Range ◽  
Clear Sky ◽  
Overall Performance ◽  
Sky Conditions ◽  
Cloud Base Height

Abstract. We developed a simple algorithm to classify clouds based on global radiation and cloud base height measured by pyranometer and ceilometer, respectively. We separated clouds into seven different classes (stratus, stratocumulus, cumulus, nimbostratus, altocumulus + altostratus, cirrus + cirrocumulus + cirrostratus and clear sky + cirrus). We also included classes for cumulus and cirrus clouds causing global radiation enhancement, and we classified multilayered clouds, when captured by the ceilometer, based on their height and characteristics (transmittance, patchiness and uniformity). The overall performance of the algorithm was nearly 70 % when compared with classification by an observer using total-sky images. The performance was best for clouds having well-distinguishable effects on solar radiation: nimbostratus clouds were classified correctly in 100 % of the cases. The worst performance corresponds to cirriform clouds (50 %). Although the overall performance of the algorithm was good, it is likely to miss the occurrences of high and multilayered clouds. This is due to the technical limits of the instrumentation: the vertical detection range of the ceilometer and occultation of the laser pulse by the lowest cloud layer. We examined the use of clearness index, which is defined as a ratio between measured global radiation and modeled radiation at the top of the atmosphere, as an indicator of clear-sky conditions. Our results show that cumulus, altocumulus, altostratus and cirriform clouds can be present when the index indicates clear-sky conditions. Those conditions have previously been associated with enhanced aerosol formation under clear skies. This is an important finding especially in the case of low clouds coupled to the surface, which can influence aerosol population via aerosol–cloud interactions. Overall, caution is required when the clearness index is used in the analysis of processes affected by partitioning of radiation by clouds.

A 42 year inference of cloud base height trends in the Luquillo Mountains of northeastern Puerto Rico

2018 ◽  
Vol 76 (1) ◽  
pp. 87-94 ◽  
Author(s):  
PW Miller ◽  
TL Mote ◽  
CA Ramseyer ◽  
AE Van Beusekom ◽  
M Scholl ◽  
...  
Keyword(s):  
Puerto Rico ◽  
Cloud Base ◽  
Luquillo Mountains ◽  
Cloud Base Height

scholarly journals Uncertainty in weather and climate prediction

2011 ◽  
Vol 369 (1956) ◽  
pp. 4751-4767 ◽  
Author(s):  
Julia Slingo ◽  
Tim Palmer
Keyword(s):  
Chaos Theory ◽  
Model Uncertainty ◽  
Lead Times ◽  
Probabilistic Prediction ◽  
Climate Forecasting ◽  
Weather And Climate ◽  
Prediction Systems ◽  
The 1960S ◽  
Support Decision Making ◽  
Adaptation And Mitigation

Following Lorenz's seminal work on chaos theory in the 1960s, probabilistic approaches to prediction have come to dominate the science of weather and climate forecasting. This paper gives a perspective on Lorenz's work and how it has influenced the ways in which we seek to represent uncertainty in forecasts on all lead times from hours to decades. It looks at how model uncertainty has been represented in probabilistic prediction systems and considers the challenges posed by a changing climate. Finally, the paper considers how the uncertainty in projections of climate change can be addressed to deliver more reliable and confident assessments that support decision-making on adaptation and mitigation.

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