Impact of Cloud Cover on Solar Radiative Biases in Deep Convective Regimes

2005 ◽  
Vol 62 (6) ◽  
pp. 1989-2000 ◽  
Author(s):  
F. Di Giuseppe ◽  
A. M. Tompkins
Keyword(s):  
Zenith Angle ◽  
Cloud Cover ◽  
Solar Zenith Angle ◽  
Total Error ◽  
Three Dimensional ◽  
Bias Reduction ◽  
Total Cloud Cover ◽  
Correction Technique ◽  
Cloud Resolving Model ◽  
Path Direction

Abstract Conflicting claims have been made concerning the magnitude of the bias in solar radiative transfer calculations when horizontal photon transport is neglected for deep convective scenarios. The difficulty of obtaining a realistic set of cloud scenes for situations of complex cloud geometry, while certain characteristics such as total cloud cover are systematically controlled, has hindered the attempt to reach a consensus. Here, a simple alternative approach is adopted. An ensemble of cloud scenes generated by a cloud resolving model are modified by an idealized function that progressively alters the cirrus anvil coverage without affecting the realism of the scene produced. Comparing three-dimensional radiative calculations with the independent column approximation for all cloud scenes, it is found that the bias in scene albedo can reach as much as 22% when the sun is overhead and 46% at low sun angles. The bias is an asymmetrical function of cloud cover with a maximum attained at cirrus anvil cloud cover of approximately 30%–40%. With a cloud cover of 15%, the bias is half its maximum value, while it is limited for coverage exceeding 80%. The position of the peak occurs at the cloud cover coinciding with the maximum number of independent clouds present in the scene. Increasing the cloud cover past this point produces a decrease in the number of isolated clouds because of cloud merging, with a consequential bias reduction. With this systematic documentation of the biases as a function of total cloud cover, it is possible to identify two contributions to the total error: the geometrical consequences of the effective cloud cover increase at low sun angles and the true 3D scattering effect of photons deviating from the original path direction. An attempt to account for the former geometrical contribution to the 1D bias is made by performing a simple correction technique, whereby the field is sheared by the tangent of the solar zenith angle. It is found that this greatly reduces the 1D biases at low sun angles. Because of the small aspect ratio of the cirrus cloud deck, the remaining bias contribution is small in magnitude and almost independent of solar zenith angle.

scholarly journals Variability of Solar UV Index in Nepal

2017 ◽  
Vol 12 (1) ◽  
pp. 114-119 ◽  
Author(s):  
Niranjan Prasad Sharma
Keyword(s):  
Data Analysis ◽  
Sea Level ◽  
Zenith Angle ◽  
Seasonal Variations ◽  
Cloud Cover ◽  
Solar Zenith Angle ◽  
Atmospheric Parameters ◽  
Uv Index ◽  
Uv Irradiance ◽  
Solar Uv

The paper presents the variability of solar UV index in main cities of Nepal. The latitude and longitude of the cities are (27.72°N, 85.32°E), ( 28.22°N, 83.32°E) and (26.45°N 87.27°E) are located at an elevation of 1350m, 800m and 72m respectively from the sea level. The NILU- UV irradiance meter of serial number (135, 137 and 133) was used to record UV radiation on these stations.  From the measurement and data analysis it was found that there were distinct diurnal, hourly mean and spring variations in the UV index. The UV index is primarily controlled by solar zenith angle for both the diurnal and seasonal variations. The highest values of hourly mean UV index was found at noon time in all seasons. Atmospheric parameters such as Solar Zenith angle (SZA), Cloud cover, aerosols  and Ozone contribute to the daily fuctuations in the UV Index. The UV Index was found to be 8.72, 9.9 and 9.2 in June 9, in Kathmandu (KTM), Pokhara (PKR) and Biratnagar (BRT).While the UV Index (UVI) in September 27 was found to be 8.52, 8.18 and 9.36 in KTM, PKR and BRT respectively. Daily mean highest UV Index before monsoon at PKR was found to be 10.6 and 8.98 at day number 144 and 100.Journal of the Institute of Engineering, 2016, 12(1): 114-119

scholarly journals The Influence of Solar Zenith Angle and Cloud Type on Cloud Radiative Forcing at the Surface in the Arctic

1999 ◽  
Vol 12 (1) ◽  
pp. 147-158 ◽  
Author(s):  
Peter J. Minnett
Keyword(s):  
Zenith Angle ◽  
Radiative Forcing ◽  
Cloud Cover ◽  
Solar Zenith Angle ◽  
Surface Radiation ◽  
Infrared Heating ◽  
Radiation Budget ◽  
The Arctic ◽  
Cloud Type ◽  
Surface Radiation Budget

Abstract Measurements of the long- and shortwave incident radiation taken from the USCGC Polar Sea during a research cruise to the Northeast Water Polynya during the summer of 1993 are analyzed together with observations of cloud type and amount to determine the effects of summertime Arctic clouds on the surface radiation budget. It is found that the solar zenith angle is critical in determining whether clouds heat or cool the surface. For large solar zenith angles (>∼80°) the infrared heating effect of clouds is greater than the reduction in insolation caused by clouds, and the surface is heated by the presence of cloud. For smaller zenith angles, cloud cover cools the surface, and for intermediate zenith angles, the surface radiation budget is insensitive to the presence of, or changes in, cloud cover.

Top-of-atmosphere albedo bias from neglecting three-dimensional cloud radiative effects

2021 ◽  
Author(s):  
Clare E. Singer ◽  
Ignacio Lopez-Gomez ◽  
Xiyue Zhang ◽  
Tapio Schneider
Keyword(s):  
Radiative Transfer ◽  
Zenith Angle ◽  
Solar Zenith Angle ◽  
3D Structure ◽  
Three Dimensional ◽  
Radiative Flux ◽  
Monte Carlo Code ◽  
Radiative Effects ◽  
Cloud Radiative Effects ◽  
The Impact

AbstractClouds cover on average nearly 70% of Earth’s surface and regulate the global albedo. The magnitude of the shortwave reflection by clouds depends on their location, optical properties, and three-dimensional (3D) structure. Due to computational limitations, Earth system models are unable to perform 3D radiative transfer calculations. Instead they make assumptions, including the independent column approximation (ICA), that neglect effects of 3D cloud morphology on albedo. We show how the resulting radiative flux bias (ICA-3D) depends on cloud morphology and solar zenith angle. We use high-resolution (20–100 m horizontal resolution) large-eddy simulations to produce realistic 3D cloud fields covering three dominant regimes of low-latitude clouds: shallow cumulus, marine stratocumulus, and deep convective cumulonimbus. A Monte Carlo code is used to run 3D and ICA broadband radiative transfer calculations; we calculate the top-of-atmosphere (TOA) reflected flux and surface irradiance biases as functions of solar zenith angle for these three cloud regimes. Finally, we use satellite observations of cloud water path (CWP) climatology, and the robust correlation between CWP and TOA flux bias in our LES sample, to roughly estimate the impact of neglecting 3D cloud radiative effects on a global scale. We find that the flux bias is largest at small zenith angles and for deeper clouds, while the albedo bias is most prominent for large zenith angles. In the tropics, the annual-mean shortwave radiative flux bias is estimated to be 3.1±1.6 W m−2, reaching as much as 6.5 W m−2 locally.

scholarly journals Precipitation and Latent Heating Distributions from Satellite Passive Microwave Radiometry. Part II: Evaluation of Estimates Using Independent Data

2006 ◽  
Vol 45 (5) ◽  
pp. 721-739 ◽  
Author(s):  
Song Yang ◽  
William S. Olson ◽  
Jian-Jian Wang ◽  
Thomas L. Bell ◽  
Eric A. Smith ◽  
...  
Keyword(s):  
Rain Rate ◽  
Sampling Error ◽  
Contextual Information ◽  
Total Error ◽  
Bias Reduction ◽  
Passive Microwave ◽  
Latent Heating ◽  
Cloud Resolving Model ◽  
Surface Rain Rate ◽  
Heating Profiles

Abstract Rainfall rate estimates from spaceborne microwave radiometers are generally accepted as reliable by a majority of the atmospheric science community. One of the Tropical Rainfall Measuring Mission (TRMM) facility rain-rate algorithms is based upon passive microwave observations from the TRMM Microwave Imager (TMI). In Part I of this series, improvements of the TMI algorithm that are required to introduce latent heating as an additional algorithm product are described. Here, estimates of surface rain rate, convective proportion, and latent heating are evaluated using independent ground-based estimates and satellite products. Instantaneous, 0.5°-resolution estimates of surface rain rate over ocean from the improved TMI algorithm are well correlated with independent radar estimates (r ∼0.88 over the Tropics), but bias reduction is the most significant improvement over earlier algorithms. The bias reduction is attributed to the greater breadth of cloud-resolving model simulations that support the improved algorithm and the more consistent and specific convective/stratiform rain separation method utilized. The bias of monthly 2.5°-resolution estimates is similarly reduced, with comparable correlations to radar estimates. Although the amount of independent latent heating data is limited, TMI-estimated latent heating profiles compare favorably with instantaneous estimates based upon dual-Doppler radar observations, and time series of surface rain-rate and heating profiles are generally consistent with those derived from rawinsonde analyses. Still, some biases in profile shape are evident, and these may be resolved with (a) additional contextual information brought to the estimation problem and/or (b) physically consistent and representative databases supporting the algorithm. A model of the random error in instantaneous 0.5°-resolution rain-rate estimates appears to be consistent with the levels of error determined from TMI comparisons with collocated radar. Error model modifications for nonraining situations will be required, however. Sampling error represents only a portion of the total error in monthly 2.5°-resolution TMI estimates; the remaining error is attributed to random and systematic algorithm errors arising from the physical inconsistency and/or nonrepresentativeness of cloud-resolving-model-simulated profiles that support the algorithm.

Effect of solar zenith angle on satellite cloud retrievals based on O2–O2 absorption band

2021 ◽  
Vol 42 (11) ◽  
pp. 4224-4240
Author(s):  
Gyuyeon Kim ◽  
Yong-Sang Choi ◽  
Sang Seo Park ◽  
Jhoon Kim
Keyword(s):  
Absorption Band ◽  
Zenith Angle ◽  
Solar Zenith Angle

Sun-induced production of vitamin D3 throughout 1 year in tropical and subtropical regions: relationship with latitude, cloudiness, UV-B exposure and solar zenith angle

2021 ◽  
Vol 20 (2) ◽  
pp. 265-274
Author(s):  
Angela C. G. B. Leal ◽  
Marcelo P. Corrêa ◽  
Michael F. Holick ◽  
Enaldo V. Melo ◽  
Marise Lazaretti-Castro
Keyword(s):  
Zenith Angle ◽  
Vitamin D3 ◽  
Solar Zenith Angle

scholarly journals The impact of atmospheric stability and wind shear on vertical cloud overlap over the Tibetan Plateau

2018 ◽  
Vol 18 (10) ◽  
pp. 7329-7343 ◽  
Author(s):  
Jiming Li ◽  
Qiaoyi Lv ◽  
Bida Jian ◽  
Min Zhang ◽  
Chuanfeng Zhao ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Wind Shear ◽  
Cloud Cover ◽  
Atmospheric Stability ◽  
Length Scale ◽  
The Tibetan Plateau ◽  
Total Cloud Cover ◽  
Atmospheric Models ◽  
The Impact ◽  
Overlap Parameter

Abstract. Studies have shown that changes in cloud cover are responsible for the rapid climate warming over the Tibetan Plateau (TP) in the past 3 decades. To simulate the total cloud cover, atmospheric models have to reasonably represent the characteristics of vertical overlap between cloud layers. Until now, however, this subject has received little attention due to the limited availability of observations, especially over the TP. Based on the above information, the main aim of this study is to examine the properties of cloud overlaps over the TP region and to build an empirical relationship between cloud overlap properties and large-scale atmospheric dynamics using 4 years (2007–2010) of data from the CloudSat cloud product and collocated ERA-Interim reanalysis data. To do this, the cloud overlap parameter α, which is an inverse exponential function of the cloud layer separation D and decorrelation length scale L, is calculated using CloudSat and is discussed. The parameters α and L are both widely used to characterize the transition from the maximum to random overlap assumption with increasing layer separations. For those non-adjacent layers without clear sky between them (that is, contiguous cloud layers), it is found that the overlap parameter α is sensitive to the unique thermodynamic and dynamic environment over the TP, i.e., the unstable atmospheric stratification and corresponding weak wind shear, which leads to maximum overlap (that is, greater α values). This finding agrees well with the previous studies. Finally, we parameterize the decorrelation length scale L as a function of the wind shear and atmospheric stability based on a multiple linear regression. Compared with previous parameterizations, this new scheme can improve the simulation of total cloud cover over the TP when the separations between cloud layers are greater than 1 km. This study thus suggests that the effects of both wind shear and atmospheric stability on cloud overlap should be taken into account in the parameterization of decorrelation length scale L in order to further improve the calculation of the radiative budget and the prediction of climate change over the TP in the atmospheric models.

scholarly journals Effects of Diurnal Variations on Tropical Equilibrium States: A Two-Dimensional Cloud-Resolving Modeling Study

2007 ◽  
Vol 64 (2) ◽  
pp. 656-664 ◽  
Author(s):  
Shouting Gao ◽  
Yushu Zhou ◽  
Xiaofan Li
Keyword(s):  
Equilibrium State ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Zenith Angle ◽  
Solar Zenith Angle ◽  
Diurnal Variations ◽  
Equilibrium States ◽  
Sea Surface ◽  
Two Dimensional ◽  
Time Invariant

Abstract Effects of diurnal variations on tropical heat and water vapor equilibrium states are investigated based on hourly data from two-dimensional cloud-resolving simulations. The model is integrated for 40 days and the simulations reach equilibrium states in all experiments. The simulation with a time-invariant solar zenith angle produces a colder and drier equilibrium state than does the simulation with a diurnally varied solar zenith angle. The simulation with a diurnally varied sea surface temperature generates a colder equilibrium state than does the simulation with a time-invariant sea surface temperature. Mass-weighted mean temperature and precipitable water budgets are analyzed to explain the thermodynamic differences. The simulation with the time-invariant solar zenith angle produces less solar heating, more condensation, and consumes more moisture than the simulation with the diurnally varied solar zenith angle. The simulation with the diurnally varied sea surface temperature produces a colder temperature through less latent heating and more IR cooling than the simulation with the time-invariant sea surface temperature.

Sign in / Sign up

Export Citation Format

Share Document