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

Show full item record



Permalink

http://hdl.handle.net/10138/321980

Citation

Ylivinkka , I , Kaupinmäki , S , Virman , M , Peltola , M , Taipale , D , Petäjä , T , Kerminen , V-M , Kulmala , M & Ezhova , E 2020 , ' Clouds over Hyytiälä, Finland : an algorithm to classify clouds based on solar radiation and cloud base height measurements ' , Atmospheric Measurement Techniques , vol. 13 , no. 10 , pp. 5595-5619 . https://doi.org/10.5194/amt-13-5595-2020

Title: Clouds over Hyytiälä, Finland : an algorithm to classify clouds based on solar radiation and cloud base height measurements
Author: Ylivinkka, Ilona; Kaupinmäki, Santeri; Virman, Meri; Peltola, Maija; Taipale, Ditte; Petäjä, Tuukka; Kerminen, Veli-Matti; Kulmala, Markku; Ezhova, Ekaterina
Contributor: University of Helsinki, Global Atmosphere-Earth surface feedbacks
University of Helsinki, INAR Physics
University of Helsinki, Aerosol-Cloud-Climate -Interactions (ACCI)
University of Helsinki, Global Atmosphere-Earth surface feedbacks
University of Helsinki, Institute for Atmospheric and Earth System Research (INAR)
University of Helsinki, Global Atmosphere-Earth surface feedbacks
University of Helsinki, Institute for Atmospheric and Earth System Research (INAR)
University of Helsinki, Institute for Atmospheric and Earth System Research (INAR)
Date: 2020-10-22
Language: eng
Number of pages: 25
Belongs to series: Atmospheric Measurement Techniques
ISSN: 1867-1381
URI: http://hdl.handle.net/10138/321980
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.
Subject: 114 Physical sciences
PARTICLE FORMATION EVENTS
VERTICAL STRUCTURE
LONG-TERM
ATMOSPHERIC NUCLEATION
STATISTICAL-MODEL
CLEAR-SKY
CLASSIFICATION
BOREAL
CEILOMETER
AEROSOLS
Rights:


Files in this item

Total number of downloads: Loading...

Files Size Format View
amt_13_5595_2020.pdf 4.394Mb PDF View/Open

This item appears in the following Collection(s)

Show full item record