Comparison of point cloudiness and sunshine derived cloud cover in India

Raju, A. J. Solomon; Kumar, K. Karuna

doi:10.1007/bf00879832

Cited by 17 publications

(7 citation statements)

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“…In previous studies involving a comparison of cloud shade with point cloudiness (Hoyt, 1977;Raju and Karuna Kumar, 1982;Rangarajan et al, 1984) monthly mean values of whole day fractional bright sunshine and point cloudiness were used. As a result, the dependence of cloud shade on solar elevation was largely masked by the whole-day averaging process.…”

Section: Analysis and Resultsmentioning

confidence: 99%

“…Conversely, the fraction of possible bright sunshine is often measured directly with a sunshine recorder from which, of course, cloud cover may be inferred. However, it has been shown that there is a systematic discrepancy between monthly mean values of cloud cover estimated by eye and the corresponding cloud cover derived from direct sunshine-recorder measurements (Brooks, 1929;Hoyt, 1977;Raju and Karuna Kumar, 1982;Rangarajan et al, 1984;Harrison and Coombes, 1986). The cloud cover estimated by eye can be higher than that derived from sunshine measurements by as much as 0.4 but this difference decreases with increasing latitude.…”

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confidence: 97%

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Influence of solar elevation on estimates of cloud cover

Coombes

Harrison

1987

Atmosphere-Ocean

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Section: Analysis and Resultsmentioning

confidence: 99%

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confidence: 97%

Influence of solar elevation on estimates of cloud cover

Coombes

Harrison

1987

Atmosphere-Ocean

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“…In some cases, ground-based observers see the sides of large vertical clouds and add them to total cloud cover. This visual error can overestimate the amount of cloud cover by 10 to 20%, or even up to (Cicenko, 1975;Raju and Karuna Kumar, 1982). Webster (1969) had noted surprisingly long sunshine durations in the presence of nearly 100% Cumulus cloud cover.…”

Section: Influence Of Selected Cloud Genera On Sunshine Duration At Noonmentioning

confidence: 99%

Influence of cloudiness on sunshine duration

Matuszko

2011

Intl Journal of Climatology

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This paper analyzes the influence of cloudiness and cloud genera on sunshine duration based on a very long homogeneous daily nephological and sunshine duration data series for the City of Krakow. Quadratic regression was used to describe the relationship between sunshine duration and cloudiness. It has been shown that cloudiness affects sunshine duration the most in June and July, and the least in December, January and February. High clouds (Cirrus, Cirrostratus, Cirrocumulus) do not interrupt the recording of sunshine duration even when they completely cover the sky. Layered clouds such as Stratus and Nimbostratus, on the other hand, do not transmit solar radiation at all. The degree of influence of different cloud genera on sunshine duration changes very little from season to season and with respect to the position of the Sun over the horizon. When the Sun is positioned higher over the horizon, clouds are less able to weaken solar radiation, resulting in larger sunshine duration values. This is especially true with respect to the following clouds: Cirrus, Cirrostratus and Cumulus. It has been shown that daytime sunshine duration patterns can be a very good indicator of cloud type and cloudiness variability. Copyright  2011 Royal Meteorological Society KEY WORDS cloudiness; cloud cover; cloud genera; sunshine duration; solar radiation; Krakow Received 24 May 2010; Revised 25 April 2011; Accepted 26 April 2011The relationship between sunshine duration and cloudiness is so obvious that it seems that there is no need to analyze it. Yet the mechanism of the impact of cloud cover on the duration of solar radiation is very complex and has not been fully analyzed to date. The climatologic literature usually treats the impact of cloudiness on sunshine duration in terms of the extent of cloud cover without taking into account the different possible cloud genera. Yet simple measurements and observations indicate that even when the sky is overcast with high clouds (e.g. Cirrostratus), solar radiation still reaches the surface of the Earth without impediment. On the other hand, layered low and middle clouds (e.g. Nimbostratus) impede direct radiation. In both cases, the sky is reported as overcast (8/8), which suggests a lack of recorded evidence of sunshine.The problem of the differential absorption and transmission of solar radiation energy by various genera of clouds, despite its fundamental significance in climate science, has not been adequately addressed thus far in the scientific literature. This may be because of the fact that clouds change constantly, thus it is challenging to adequately determine their physical properties. Groundbased weather stations report only visual cloud observations and measure the height of the cloud base. Within one such climatologic observation, several genera and species of clouds may be present at the same time, which * Correspondence to: Dorota Matuszko, Institute of Geography and Spatial Management, Jagiellonian University, ul. Gronostajowa 7, impedes the measurement of h...

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“…Chagnon (1981) found virtually the same results for the midwest United States during the period 1901-1977. Raju and Kumar (1982) argued that the fraction of possible sunshine will closely approximate the fraction of possible clear weather when averaged over long term periods in any given region, and they demonstrated how sunshine derived cloud cover in India can be considered a better measurement of actual cloud cover than visual estimates of cloudiness.…”

Section: Synoptic Obser6ations Of Cloudiness and Comparison With The mentioning

confidence: 99%

Sunshine records from Ireland: cloud factors and possible links to solar activity and cosmic rays

Πάλλη¹,

Butler²

2001

Intl Journal of Climatology

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The records of sunshine hours obtained since the late 19th century from four stations distributed throughout Ireland were analysed. A gradual decrease in sunshine hours has occurred at all four sites since records began. Increasing cloud factors, resulting from enhanced evaporation rates over the Atlantic as sea surface temperatures have risen, is one possible explanation for the decline in sunshine.A strong negative correlation was confirmed between sunshine factors from ground-based observations and satellite-based cloud factors over Ireland. In addition, it was found that cloud factors over Ireland correlated well with cloud factors over large oceanic areas such as the North Atlantic and mid-high latitudes generally. Thus cloud factors (and similarly sunshine factors) from regions on the boundaries of large oceans which lie in the direction of the prevailing wind could be useful in determining the long-term changes in cloud factors over more extended areas. Knowledge of such long term variability in the Earth's cloud cover is important input information for modelling past climate change.The importance of cosmic rays as a link between solar activity and climate was assessed from a study of the ISCCP-D2 satellite cloud factors and Irish sunshine data. Whilst these results confirmed the strong correlation between total cloud factor and cosmic rays over non-tropical oceans between 1984 and 1991 previously reported, it was found that this correlation did not hold in the subsequent period 1991 -1994. Other work has established a link through specifically low cloud.Indirect evidence of cloud formation by cosmic rays from a variation in the sunshine factor following Forbush decreases, and over the sunspot cycle, was mostly negative. Although a dip at seven years past sunspot minimum is evident in the sunshine factor for all four sites and in most seasons, it is of marginal statistical significance. Copyright

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Comparison of point cloudiness and sunshine derived cloud cover in India

Cited by 17 publications

References 7 publications

Influence of solar elevation on estimates of cloud cover

Influence of solar elevation on estimates of cloud cover

Influence of cloudiness on sunshine duration

Sunshine records from Ireland: cloud factors and possible links to solar activity and cosmic rays

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