scholarly journals The relationship between low-level cloud amount and its proxies over the globe by cloud type

2020 ◽  
Vol 20 (5) ◽  
pp. 3041-3060
Author(s):  
Jihoon Shin ◽  
Sungsu Park
Keyword(s):  
Cloud Amount ◽  
Superior Performance ◽  
Cloud Type ◽  
Low Level ◽  
Incorrect Diagnosis ◽  
Stratiform Clouds ◽  
Extended Analysis ◽  
Inversion Strength ◽  
Lifting Condensation Level ◽  
The Relationship

Abstract. We extend upon previous work to examine the relationship between low-level cloud amount (LCA) and various proxies for LCA – estimated low-level cloud fraction (ELF), lower tropospheric stability (LTS), and estimated inversion strength (EIS) – by low-level cloud type (CL) over the globe using individual surface and upper-air observations. Individual CL has its own distinct environmental structure, and therefore our extended analysis by CL can provide insights into the strengths and weaknesses of various proxies and help to improve them. Overall, ELF performs better than LTS and EIS in diagnosing the variations in LCA among various CLs, indicating that a previously identified superior performance of ELF compared to LTS and EIS as a global proxy for LCA comes from its realistic correlations with various CLs rather than with a specific CL. However, ELF, LTS, and EIS have a problem in diagnosing the changes in LCA when noCL (no low-level cloud) is reported and also when Cu (cumulus) is reported over deserts where background stratus does not exist. This incorrect diagnosis of noCL as a cloudy condition is more clearly seen in the analysis of individual CL frequencies binned by proxy values. If noCL is excluded, ELF, LTS, and EIS have good inter-CL correlations with the amount when present (AWP) of individual CLs. In the future, an advanced ELF needs to be formulated to deal with the decrease in LCA when the inversion base height is lower than the lifting condensation level to diagnose cumulus updraft fraction, as well as the amount of stratiform clouds and detrained cumulus, and to parameterize the scale height as a function of appropriate environmental variables.

scholarly journals The Relationship between Low-Level Cloud Amount and Its Proxies over the Globe by Cloud Types

2019 ◽  
Author(s):  
Jihoon Shin ◽  
Sungsu Park
Keyword(s):  
Cloud Amount ◽  
Superior Performance ◽  
Low Level ◽  
Incorrect Diagnosis ◽  
Stratiform Clouds ◽  
Extended Analysis ◽  
Inversion Strength ◽  
Lifting Condensation Level ◽  
The Relationship ◽  
Better Than

Abstract. We extend upon previous work to examine the relationship between low-level cloud amount (LCA) and various proxies for LCA – estimated low-level cloud fraction (ELF), lower-tropospheric stability (LTS), estimated inversion strength (EIS), and estimated cloud-top entrainment index (ECTEI) – by low-level cloud types (CL) over the globe using individual surface and upper-air observations. Individual CL has its own distinct environmental structure, and therefore our extended analysis by CL can provide insights into the strength and weakness of various proxies and help to improve them. Overall, ELF performs better than LTS/EIS in diagnosing the variations in LCA among various CLs, indicating that a previously identified superior performance of ELF to LTS/EIS as a global proxy for LCA comes from its realistic correlations with various CLs rather than with a specific CL. However, ELF as well as LTS/EIS has a problem in diagnosing the decrease in LCA when CL0 (no low-level cloud) is reported and the increase of LCA when CL12 (cumulus) is reported over the deserts where background stratus does not exist. This incorrect diagnosis of CL0 as a cloudy condition is more clearly seen in the analysis of individual CL frequencies binned by proxy values. If CL0 is excluded, all ELF/LTS/EIS have good inter-CL correlations with the amount-when-present (AWP) of individual CLs. In future, an advanced ELF needs to be formulated to deal with the dissipation of LCA when the inversion base height is lower than the lifting condensation level, to diagnose cumulus updraft fraction as well as the amount of stratiform clouds and detrained cumulus, and to parameterize the scale height as a function of appropriate environmental variables.

scholarly journals Heuristic estimation of low-level cloud fraction over the globe based on a decoupling parameterization

2019 ◽  
Vol 19 (8) ◽  
pp. 5635-5660 ◽  
Author(s):  
Sungsu Park ◽  
Jihoon Shin
Keyword(s):  
General Circulation ◽  
Cloud Amount ◽  
Cloud Fraction ◽  
Spatiotemporal Variation ◽  
Interannual Variations ◽  
Marine Stratocumulus ◽  
Near Surface ◽  
Low Level ◽  
Inversion Strength ◽  
Lifting Condensation Level

Abstract. Based on the decoupling parameterization of the cloud-topped planetary boundary layer, a simple equation is derived to compute the inversion height. In combination with the lifting condensation level and the amount of water vapor in near-surface air, we propose a low-level cloud suppression parameter (LCS) and estimated low-level cloud fraction (ELF), as new proxies for the analysis of the spatiotemporal variation of the global low-level cloud amount (LCA). Individual surface and upper-air observations are used to compute LCS and ELF as well as lower-tropospheric stability (LTS), estimated inversion strength (EIS), and estimated cloud-top entrainment index (ECTEI), three proxies for LCA that have been widely used in previous studies. The spatiotemporal correlations between these proxies and surface-observed LCA were analyzed. Over the subtropical marine stratocumulus deck, both LTS and EIS diagnose seasonal–interannual variations of LCA well. However, their use as a global proxy for LCA is limited due to their weaker and inconsistent relationship with LCA over land. EIS is anti-correlated with the decoupling strength more strongly than it is correlated with the inversion strength. Compared with LTS and EIS, ELF and LCS better diagnose temporal variations of LCA, not only over the marine stratocumulus deck but also in other regions. However, all proxies have a weakness in diagnosing interannual variations of LCA in several subtropical stratocumulus decks. In the analysis using all data, ELF achieves the best performance in diagnosing spatiotemporal variation of LCA, explaining about 60 % of the spatial–seasonal–interannual variance of the seasonal LCA over the globe, which is a much larger percentage than those explained by LTS (2 %) and EIS (4 %). Our study implies that accurate prediction of inversion base height and lifting condensation level is a key factor necessary for successful simulation of global low-level clouds in general circulation models (GCMs). Strong spatiotemporal correlation between ELF (or LCS) and LCA identified in our study can be used to evaluate the performance of GCMs, identify the source of inaccurate simulation of LCA, and better understand climate sensitivity.

scholarly journals Heuristic Estimation of Low-Level Cloud Fraction over the Globe Based on a Decoupling Parameterization

2019 ◽  
Author(s):  
Sungsu Park ◽  
Jihoon Shin
Keyword(s):  
General Circulation ◽  
Cloud Amount ◽  
Cloud Fraction ◽  
Spatiotemporal Variation ◽  
Interannual Variations ◽  
Marine Stratocumulus ◽  
Near Surface ◽  
Low Level ◽  
Inversion Strength ◽  
Lifting Condensation Level

Abstract. Based on the decoupling parameterization of the cloud-topped planetary boundary layer, a simple equation is derived to compute the inversion height. In combination with the lifting condensation level and the amount of water vapor in near-surface air, we propose a low-level cloud suppression parameter (LCS) and estimated low-level cloud fraction (ELF), as new proxies for the analysis of the spatiotemporal variation of the global low-level cloud amount (LCA). Individual surface and upper-air observations are used to compute LCS and ELF as well as lower-tropospheric stability (LTS), estimated inversion strength (EIS), and estimated cloud-top entrainment index (ECTEI), three proxies for LCA that have been widely used in previous studies. The spatiotemporal correlations between these proxies and surface-observed LCA were analyzed. Over the subtropical marine stratocumulus deck, both LTS and EIS well diagnose seasonal-interannual variations of LCA. However, their use as global proxy for LCA is limited due to their weaker and inconsistent relationship with LCA over land. EIS is anti-correlated with the decoupling strength more strongly than it is correlated with the inversion strength. Compared with LTS and EIS, ELF and LCS better diagnose temporal variations of LCA, not only over the marine stratocumulus deck but also in other regions. However, all proxies have a weakness in diagnosing interannual variations of LCA in several subtropical stratocumulus decks. In the analysis using all data, ELF achieves the best performance in diagnosing spatiotemporal variation of LCA, explaining about 60 % of the spatial-seasonal-interannnual variance of the seasonal LCA over the globe, which is a much larger percentage than those explained by LTS (2 %) and EIS (4 %). Our study implies that accurate prediction of inversion base height and lifting condensation level is a key factor necessary for successful simulation of global low-level clouds in general circulation models (GCMs). Strong spatiotemporal correlation between ELF (or LTS) and LCA identified in our study can be used to evaluate the performance of GCMs, identify the source of inaccurate simulation of LCA, and better understand climate sensitivity.

scholarly journals Breakup of nocturnal low-level stratiform clouds during the southern West African monsoon season

2021 ◽  
Vol 21 (3) ◽  
pp. 2027-2051
Author(s):  
Maurin Zouzoua ◽  
Fabienne Lohou ◽  
Paul Assamoi ◽  
Marie Lothon ◽  
Véronique Yoboue ◽  
...  
Keyword(s):  
West Africa ◽  
Early Morning ◽  
Cloud Formation ◽  
Cloud Base ◽  
Liquid Water Path ◽  
Stratiform Cloud ◽  
Low Level ◽  
Convective Clouds ◽  
Stratiform Clouds ◽  
Lifting Condensation Level

Abstract. Within the framework of the DACCIWA (Dynamics–Aerosol–Chemistry–Cloud Interactions in West Africa) project and based on a field experiment conducted in June and July 2016, we analyze the daytime breakup of continental low-level stratiform clouds in southern West Africa. We use the observational data gathered during 22 precipitation-free occurrences at Savè, Benin. Our analysis, which starts from the stratiform cloud formation usually at night, focuses on the role played by the coupling between cloud and surface in the transition towards shallow convective clouds during daytime. It is based on several diagnostics, including the Richardson number and various cloud macrophysical properties. The distance between the cloud base height and lifting condensation level is used as a criterion of coupling. We also make an attempt to estimate the most predominant terms of the liquid water path budget in the early morning. When the nocturnal low-level stratiform cloud forms, it is decoupled from the surface except in one case. In the early morning, the cloud is found coupled with the surface in 9 cases and remains decoupled in the 13 other cases. The coupling, which occurs within the 4 h after cloud formation, is accompanied by cloud base lowering and near-neutral thermal stability in the subcloud layer. Further, at the initial stage of the transition, the stratiform cloud base is slightly cooler, wetter and more homogeneous in coupled cases. The moisture jump at the cloud top is usually found to be lower than 2 g kg−1 and the temperature jump within 1–5 K, which is significantly smaller than typical marine stratocumulus and explained by the monsoon flow environment in which the stratiform cloud develops over West Africa. No significant difference in liquid water path budget terms was found between coupled and decoupled cases. In agreement with previous numerical studies, we found that the stratiform cloud maintenance before sunrise results from the interplay between the predominant radiative cooling, entrainment and large-scale subsidence at its top. Three transition scenarios were observed depending on the state of coupling at the initial stage. In coupled cases, the low-level stratiform cloud remains coupled until its breakup. In five of the decoupled cases, the cloud couples with the surface as the lifting condensation level rises. In the eight remaining cases, the stratiform cloud remains hypothetically decoupled from the surface throughout its life cycle since the height of its base remains separated from the condensation level. In cases of coupling during the transition, the stratiform cloud base lifts with the growing convective boundary layer roughly between 06:30 and 08:00 UTC. The cloud deck breakup, occurring at 11:00 UTC or later, leads to the formation of shallow convective clouds. When the decoupling subsists, shallow cumulus clouds form below the stratiform cloud deck between 06:30 and 09:00 UTC. The breakup time in this scenario has a stronger variability and occurs before 11:00 UTC in most cases. Thus, we argue that the coupling with the surface during daytime hours has a crucial role in the low-level stratiform cloud maintenance and its transition towards shallow convective clouds.

scholarly journals How Has Subtropical Stratocumulus and Associated Meteorology Changed since the 1980s?*

2015 ◽  
Vol 28 (21) ◽  
pp. 8396-8410 ◽  
Author(s):  
C. Seethala ◽  
Joel R. Norris ◽  
Timothy A. Myers
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Meteorological Parameters ◽  
Cloud Amount ◽  
Sea Surface ◽  
Independent Effect ◽  
Multilinear Regression ◽  
Low Level ◽  
Observational Uncertainty ◽  
Inversion Strength

Abstract The importance of low-level cloud feedbacks to climate sensitivity motivates an investigation of how low-level cloud amount and related meteorological conditions have changed in recent decades in subtropical stratocumulus regions. Using satellite cloud datasets corrected for inhomogeneities, it is found that during 1984–2009 low-level cloud amount substantially increased over the northeastern Pacific, southeastern Pacific, and southeastern Atlantic; decreased over the northeastern Atlantic; and weakly increased over the southeastern Indian Ocean subtropical stratocumulus regions. Examination of meteorological parameters from four reanalyses indicates that positive trends in low-level cloud amount are associated with cooler sea surface temperature, greater inversion strength, and enhanced cold-air advection. The converse holds for negative trends in low-level cloud amount. A multilinear regression model based on these three meteorological variables reproduces the sign and magnitude of observed cloud amount trends in all stratocumulus regions within the range of observational uncertainty. Changes in inversion strength have the largest independent effect on cloud trends, followed by changes in advection strength. Changes in sea surface temperature have the smallest independent effect on cloud trends. Differing signs of cloud trends and differing contributions from meteorological parameters suggest that observed changes in subtropical stratocumulus since the 1980s may be due to natural variability rather than a systematic response to climate change.

Creativity from paradoxical experience: a theory of how individuals achieve creativity while adopting paradoxical frames

2019 ◽  
Vol 23 (3) ◽  
pp. 397-418 ◽  
Author(s):  
Goran Calic ◽  
Sebastien Hélie ◽  
Nick Bontis ◽  
Elaine Mosakowski
Keyword(s):  
Cognitive Processes ◽  
Computational Simulation ◽  
Current Theory ◽  
Superior Performance ◽  
Cognitive Mechanisms ◽  
Content Type ◽  
Important Benefit ◽  
Paradox Theory ◽  
Stored Information ◽  
The Relationship

PurposeExtant paradox theory suggests that adopting paradoxical frames, which are mental templates adopted by individuals in order to embrace contradictions, will result in superior firm performance. Superior performance is achieved through learning and creativity, fostering flexibility and resilience and unleashing human capital. The creativity mechanism of paradox theory is limited by a few propositions and a rough underlying theoretical logic. Using the extant theoretical base as a platform, the paper aims to develop a more powerful theory using a computational simulation.Design/methodology/approachThis paper relies on a psychologically realistic computer simulation. Using a simulation to generate ideas from stored information, one can model and manipulate the parameters that have been shown to mediate the relationship between paradoxes and creative output – defined as the number of creative ideas generated.FindingsSimulation results suggest that the relationship between paradoxical frames and creative output is non-monotonic – contrary to previous studies. Indeed, findings suggest that paradoxical frames can reduce, rather than enhance, creative output, in at least some cases.Originality/valueAn important benefit of adopting paradoxical frames is their capacity to increase creative output. This assumption is challenging to test, because one cannot measure private cognitive processes related to knowledge creation. However, they can be simulated. This allows for the extension of current theory. This new theory depicts a more complete relationship between paradoxical frames and creativity by accounting for subjective differences in how paradoxical frames are experienced along two cognitive mechanisms – differentiation and integration.

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