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

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.

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

10.5194/amt-2020-130 ◽

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.

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

Remote Sensing ◽

10.3390/rs11242900 ◽

2019 ◽

Vol 11 (24) ◽

pp. 2900 ◽

Cited By ~ 2

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.

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

10.5194/ems2021-197 ◽

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>&#160;</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.&#160; 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>

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25 years of Cloud Base Height Measurements by Ceilometer in Ny Ålesund, Svalbard

10.5194/essd-2018-48 ◽

2018 ◽

Author(s):

Marion Maturilli ◽

Kerstin Ebell

Keyword(s):

Time Series ◽

Cloud Cover ◽

The Arctic ◽

Cloud Base ◽

High Temporal Resolution ◽

Radiation Balance ◽

Essential Information ◽

Data Record ◽

Cloud Base Height

Abstract. Clouds are a key factor for the Arctic Amplification of global warming, but their actual appearance and distribution is still afflicted with large uncertainty. On the Arctic wide scale, large discrepancies are found between the various reanalyses and satellite products, respectively. Although ground-based observations by remote sensing are limited to point measurements, they have the advantage to obtain extended time series of vertically resolved cloud properties. Here, we present a 25-year data record of cloud base height measured by ceilometer at the Arctic site Ny-Ålesund, Svalbard. Linked to cyclonic activity, the cloud base height provides essential information for the interpretation of the surface radiation balance and contributes to the understanding meteorological processes. Furthermore, it is a useful auxiliary component for the analysis of advanced technologies that provide insight to cloud microphysical properties, like the cloud radar. The long-term time series also allows deriving an annual cycle of the cloud occurrence frequency, revealing the more frequent cloud cover in summer and the lowest cloud cover amount in April. However, as the use of different ceilometer instruments over the years potentially imposed inhomogeneities to the data record, any long-term trend analysis should be avoided. The Ny-Ålesund cloud base height data from August 1992 to July 2017 are provided in high temporal resolution of 5 minutes (1 minute) before (after) July 1998, respectively, at the PANGAEA repository (https://doi.org/10.1594/PANGAEA.880300).

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

Atmospheric Measurement Techniques ◽

10.5194/amt-13-5595-2020 ◽

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.

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