scholarly journals Quantifying Transition Zone Radiative Effects in Longwave Radiation Parameterizations

2020 ◽  
Vol 47 (22) ◽  
Author(s):  
Babak Jahani ◽  
Josep Calbó ◽  
Josep‐Abel González
Keyword(s):  
Transition Zone ◽  
Longwave Radiation ◽  
Radiative Effects ◽  
Radiation Parameterizations

scholarly journals Solar radiation, cloudiness and longwave radiation over low-latitude glaciers: implications for mass-balance modelling

2009 ◽  
Vol 55 (190) ◽  
pp. 292-302 ◽  
Author(s):  
Thomas Mölg ◽  
Nicolas J. Cullen ◽  
Georg Kaser
Keyword(s):  
Mass Balance ◽  
Global Radiation ◽  
Longwave Radiation ◽  
Balance Model ◽  
Glacier Mass Balance ◽  
Peruvian Andes ◽  
Tropical Glaciers ◽  
Clear Sky ◽  
Physically Based ◽  
Radiation Parameterizations

AbstractBroadband radiation schemes (parameterizations) are commonly used tools in glacier mass-balance modelling, but their performance at high altitude in the tropics has not been evaluated in detail. Here we take advantage of a high-quality 2 year record of global radiation (G ) and incoming longwave radiation (L ↓) measured on Kersten Glacier, Kilimanjaro, East Africa, at 5873 m a.s.l., to optimize parameterizations of G and L ↓. We show that the two radiation terms can be related by an effective cloud-cover fraction neff , so G or L ↓ can be modelled based on neff derived from measured L ↓ or G, respectively. At neff = 1, G is reduced to 35% of clear-sky G, and L ↓ increases by 45–65% (depending on altitude) relative to clear-sky L ↓. Validation for a 1 year dataset of G and L ↓ obtained at 4850 m on Glaciar Artesonraju, Peruvian Andes, yields a satisfactory performance of the radiation scheme. Whether this performance is acceptable for mass-balance studies of tropical glaciers is explored by applying the data from Glaciar Artesonraju to a physically based mass-balance model, which requires, among others, G and L ↓ as forcing variables. Uncertainties in modelled mass balance introduced by the radiation parameterizations do not exceed those that can be caused by errors in the radiation measurements. Hence, this paper provides a tool for inclusion in spatially distributed mass-balance modelling of tropical glaciers and/or extension of radiation data when only G or L ↓ is measured.

scholarly journals Longwave Radiative Effect of the Cloud-Aerosol Transition Zone Based on CERES Observations

2021 ◽  
Author(s):  
Babak Jahani ◽  
Hendrik Andersen ◽  
Josep Calbó ◽  
Josep-Abel González ◽  
Jan Cermak
Keyword(s):  
Radiative Transfer ◽  
Transition Zone ◽  
Radiant Energy ◽  
Energy System ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Radiative Effect ◽  
Radiative Effects ◽  
Clear Sky ◽  
Moderate Resolution Imaging Spectroradiometer

Abstract. This study presents an approach for quantification of cloud-aerosol transition zone broadband longwave radiative effects at the top of the atmosphere (TOA) during daytime over the ocean, based on satellite observations and radiative transfer simulation. Specifically, we used several products from MODIS (Moderate Resolution Imaging Spectroradiometer) and CERES (Clouds and the Earth’s Radiant Energy System) sensors for identification and selection of CERES footprints with horizontally homogeneous transition zone and clear-sky conditions. For the selected transition zone footprints, radiative effect was calculated as the difference between the instantaneous CERES TOA upwelling broadband longwave radiance observations and corresponding clear-sky radiance simulations. The clear-sky radiances were simulated using the Santa Barbara DISORT Atmospheric Radiative Transfer model fed by the hourly ERA5 reanalysis (fifth generation ECMWF reanalysis) atmospheric and surface data. The CERES radiance observations corresponding to the clear-sky footprints detected were also used for validating the simulated clear-sky radiances. We tested this approach using the radiative measurements made by the MODIS and CERES instruments onboard Aqua platform over the south-eastern Atlantic Ocean during August 2010. For the studied period and domain, transition zone radiative effect (given in flux units) is on average equal to 8.0 ± 3.7 W m−2 (heating effect; median: 5.4 W m−2), although cases with radiative effects as large as 50 W m−2 were found.

Longwave Radiation at the Cloud-Aerosol Transition Zone from Radiative Parameterizations in Weather Research and Forecasting Model (WRF)

2020 ◽  
Author(s):  
Babak Jahani ◽  
Josep Calbó ◽  
Josep-Abel González
Keyword(s):  
Transition Zone ◽  
Atmospheric Aerosol ◽  
Longwave Radiation ◽  
Suspended Particles ◽  
Weather Research And Forecasting ◽  
Forecasting Model ◽  
Liquid Droplets ◽  
Mixing Ratios ◽  
Free Air ◽  
Weather Research

<p>There are conditions between cloudy and cloud-free air at which it is hard to define the suspended particles in the atmosphere either as a cloud or an atmospheric aerosol; it is called twilight or transition zone. This occurs when characteristics of the suspended particles are between those corresponding to a pure cloud and those corresponding to a pure atmospheric aerosol. However, in most meteorological and climate studies the condition of sky is assumed to be either cloudy (fully developed cloud) or cloud-free (dry aerosol), neglecting the transition zone. The present communication aims to show the uncertainties introduced by this simplified assumption in modeling longwave radiation. For this purpose, the parameterizations RRTMG, NewGoddard and FLG included in the Weather Research and Forecasting Model (WRF) version 4.0 were isolated from the whole model. These parameterizations were then used to perform a number of simulations under ideal “cloud” and “aerosol” modes, for different values of (i) cloud optical thicknesses resulting from different sizes of ice crystals or liquid droplets, cloud height, mixing ratios; and (ii) different aerosol optical thicknesses combined with various aerosol types. The differences in the resulting longwave radiative effects (RE) at the top of the atmosphere and at the Earth surface were analyzed. The primary results show: (1) the parameterization RRTMG is not capable of simulating the REs of the aerosols in the longwave region, (2) different assumptions of a situation corresponding to the transition zone lead to a mean relative uncertainty of about 170% in the estimated longwave irradiance at both top of the atmosphere and surface, (3) the absolute uncertainties observed in the surface downwelling irradiances are substantially greater than those relating to the upwelling irradiances at top of the atmosphere.</p>

scholarly journals Assessing the Radiative Effects of Global Ice Clouds Based on CloudSat and CALIPSO Measurements

2016 ◽  
Vol 29 (21) ◽  
pp. 7651-7674 ◽  
Author(s):  
Yulan Hong ◽  
Guosheng Liu ◽  
J.-L. F. Li
Keyword(s):  
Longwave Radiation ◽  
Cooling Effect ◽  
Radiation Budget ◽  
Radiative Effect ◽  
Radiative Effects ◽  
Ice Clouds ◽  
Cloud Optical Depth ◽  
Ice Cloud ◽  
Heating And Cooling ◽  
The Tropics

Abstract Although it is well established that cirrus warms Earth, the radiative effect of the entire spectrum of ice clouds is not well understood. In this study, the role of all ice clouds in Earth’s radiation budget is investigated by performing radiative transfer modeling using ice cloud properties retrieved from CloudSat and CALIPSO measurements as inputs. Results show that, for the 2008 period, the warming effect (~21.8 ± 5.4 W m−2) induced by ice clouds trapping longwave radiation exceeds their cooling effect (~−16.7 ± 1.7 W m−2) caused by shortwave reflection, resulting in a net warming effect (~5.1 ± 3.8 W m−2) globally on the earth–atmosphere system. The net warming is over 15 W m−2 in the tropical deep convective regions, whereas cooling occurs in the midlatitudes, which is less than 10 W m−2 in magnitude. Seasonal variations of ice cloud radiative effects are evident in the midlatitudes where the net effect changes from warming during winter to cooling during summer, whereas warming occurs all year-round in the tropics. Ice cloud optical depth τ is shown to be an important factor in determining the sign and magnitude of the net radiative effect. Ice clouds with τ < 4.6 display a warming effect with the largest contributions from those with τ ≈ 1.0. In addition, ice clouds cause vertically differential heating and cooling of the atmosphere, particularly with strong heating in the upper troposphere over the tropics. At Earth’s surface, ice clouds produce a cooling effect no matter how small the τ value is.

scholarly journals On the use of incoming longwave radiation parameterizations in a glacier environment

2008 ◽  
Vol 2 (4) ◽  
pp. 487-511 ◽  
Author(s):  
J. Sedlar ◽  
R. Hock
Keyword(s):  
Meteorological Data ◽  
Global Radiation ◽  
Correlation Coefficients ◽  
Longwave Radiation ◽  
Near Surface ◽  
Clear Sky ◽  
Radiation Parameterizations ◽  
Cloud Parameterization ◽  
Sky Conditions ◽  
Parameter Values

Abstract. Energy balance based glacier melt models require accurate estimates of incoming longwave radiation since it is generally the largest source of energy input. Multi-year near-surface meteorological data from Storglaciären, northern Sweden, were used to evaluate commonly used longwave radiation parameterizations in a glacier environment under clear-sky, overcast-sky and all-sky conditions. The tested parameterization depending solely on air temperature performed worse than those including also air humidity. Adopting parameter values from the literature instead of fitting them to the data resulted in similar correlation coefficients between modeled and measured radiation, but generated larger biases, emphasizing the need to derive site-specific coefficients. Nearly all models including those fitted to the data tended to overestimate longwave radiation during periods of low longwave radiation, and vice versa when radiation input was high. An attempt was made to parameterize cloud cover using top of atmosphere and measured global radiation. Both hourly and daily calculations of incoming longwave radiation using the cloud parameterization provided similar, or even stronger, correlations to the measurements compared to using observed cloud fraction as input. Using the global radiation cloud parameterization is promising for use in high-latitude regions where global radiation measurements exist but cloud observations do not.

Shortwave Heating Rate at the Cloud-Aerosol Transition Zone from Radiative Parameterizations in the Weather Research and Forecasting Model (WRF)

2020 ◽  
Author(s):  
Josep Calbó ◽  
Babak Jahani ◽  
Josep-Abel González
Keyword(s):  
Heating Rate ◽  
Transition Zone ◽  
Atmospheric Aerosols ◽  
Shortwave Radiation ◽  
Weather Research And Forecasting ◽  
Forecasting Model ◽  
Liquid Droplets ◽  
Mixing Ratios ◽  
Radiation Parameterizations ◽  
Weather Research

<p>The conditions between cloudy and cloud-free air, named “Transition (or twilight) Zone”, are a major source of uncertainty in the climate and meteorological studies. The transition zone involves microphysical and radiative characteristics which lay on the border between those corresponding to a pure cloud and those corresponding to pure atmospheric aerosols. Several studies show that a notable proportion of cloudless sky at any time may correspond to this phase. However, as the information available about radiative effects of this phase is still very limited in most meteorological and climate studies the condition of sky is assumed to be either cloudy (fully developed cloud) or cloud-free (dry aerosol), neglecting the transition zone. This implies that these models consider the area/layer corresponding to the transition zone as either cloud or aerosol. The authors of the current communication have shown in a previous work that there are substantial uncertainties associated with modeling the surface shortwave irradiances under this assumption [Jahani et al. (2019) JGR: Atmospheres, 124. https://doi.org/10.1029/2019JD031064]. The present communication aims to show the uncertainties in modeling the heating rate in the atmosphere (due to shortwave solar radiation) driven from different treatments of the transition zone. For this purpose, the relatively detailed shortwave radiation parameterizations included in the Weather Research and Forecasting model (WRF) version 4.0, which allow users to consider different treatments of aerosols and clouds (RRTMG, NewGoddard and FLG), were isolated from the whole model. These parameterizations were then utilized to perform a number of simulations under ideal “cloud” and “aerosol” modes, for different values of (i) cloud optical thicknesses resulting from different sizes of ice crystals or liquid droplets, cloud height, mixing ratios; and (ii) different aerosol optical thicknesses combined with various aerosol types. The optical thickness under both aerosol and cloud modes was considered to vary between 0.01 and 2.00. The differences in the resulting atmosphere column averaged heating rate were analyzed. The results showed (i) the simplified assumption about the state of the sky leads to a large difference among the atmospheric shortwave heating rate, (ii) magnitude of these uncertainties is higher when parameterizations which cope with the Radiative Transfer Equation in more detail (RRTMG and NewGoddard) are used.</p>

scholarly journals Testing longwave radiation parameterizations under clear and overcast skies at Storglaciären, Sweden

2009 ◽  
Vol 3 (1) ◽  
pp. 75-84 ◽  
Author(s):  
J. Sedlar ◽  
R. Hock
Keyword(s):  
Meteorological Data ◽  
Water Vapor Pressure ◽  
Longwave Radiation ◽  
Cloud Fraction ◽  
Shortwave Radiation ◽  
Mean Bias Error ◽  
Bias Error ◽  
Near Surface ◽  
Radiation Parameterizations ◽  
Sky Conditions

Abstract. Energy balance based glacier melt models require accurate estimates of incoming longwave radiation but direct measurements are often not available. Multi-year near-surface meteorological data from Storglaciären, Northern Sweden, were used to evaluate commonly used longwave radiation parameterizations in a glacier environment under clear-sky and all-sky conditions. Parameterizations depending solely on air temperature performed worse than those which include water vapor pressure. All models tended to overestimate incoming longwave radiation during periods of low longwave radiation, while incoming longwave was underestimated when radiation was high. Under all-sky conditions root mean square error (RMSE) and mean bias error (MBE) were 17 to 20 W m−2 and −5 to 1 W m−2, respectively. Two attempts were made to circumvent the need of cloud cover data. First cloud fraction was parameterized as a function of the ratio, τ, of measured incoming shortwave radiation and calculated top of atmosphere radiation. Second, τ was related directly to the cloud factor (i.e. the increase in sky emissivity due to clouds). Despite large scatter between τ and both cloud fraction and the cloud factor, resulting calculations of hourly incoming longwave radiation for both approaches were only slightly more variable with RMSE roughly 3 W m−2 larger compared to using cloud observations as input. This is promising for longwave radiation modeling in areas where shortwave radiation data are available but cloud observations are not.

scholarly journals Investigating the impact of cloud-radiative feedbacks on tropical precipitation extremes

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Brian Medeiros ◽  
Amy C. Clement ◽  
James J. Benedict ◽  
Bosong Zhang
Keyword(s):  
Extreme Precipitation ◽  
Climate Models ◽  
Longwave Radiation ◽  
Extreme Rainfall ◽  
Radiative Effects ◽  
Tropical Oceans ◽  
Cloud Radiative Effects ◽  
Radiative Feedbacks ◽  
Mean Climate ◽  
The Impact

AbstractAlthough societally important, extreme precipitation is difficult to represent in climate models. This study shows one robust aspect of extreme precipitation across models: extreme precipitation over tropical oceans is strengthened through a positive feedback with cloud-radiative effects. This connection is shown for a multi-model ensemble with experiments that make clouds transparent to longwave radiation. In all cases, tropical extreme precipitation reduces without cloud-radiative effects. Qualitatively similar results are presented for one model using the cloud-locking method to remove cloud feedbacks. The reduced extreme precipitation without cloud-radiative feedbacks does not arise from changes in the mean climate. Rather, evidence is presented that cloud-radiative feedbacks enhance organization of convection and most extreme precipitation over tropical oceans occurs within organized systems. This result suggests that climate models must correctly predict cloud structure and properties, as well as capture the essence of organized convection in order to accurately represent extreme rainfall.

scholarly journals Radiative and thermodynamic responses to aerosol extinction profiles during the pre-monsoon month over South Asia

2015 ◽  
Vol 15 (12) ◽  
pp. 16901-16943 ◽  
Author(s):  
Y. Feng ◽  
V. R. Kotamarthi ◽  
R. Coulter ◽  
C. Zhao ◽  
M. Cadeddu
Keyword(s):  
Boundary Layer ◽  
South Asia ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Lower Troposphere ◽  
Longwave Radiation ◽  
Radiative Heating ◽  
Lower Atmosphere ◽  
Radiative Effects ◽  
Aerosol Radiative

Abstract. Aerosol radiative effects and thermodynamic responses over South Asia are examined with a version of the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) for March 2012. Model results of Aerosol Optical Depth (AOD) and extinction profiles are analyzed and compared to satellite retrievals and two ground-based lidars located in the northern India. The WRF-Chem model is found to underestimate the AOD during the simulated pre-monsoon month and about 83 % of the model low-bias is due to aerosol extinctions below ~2 km. Doubling the calculated aerosol extinctions below 850 hPa generates much better agreement with the observed AOD and extinction profiles averaged over South Asia. To separate the effect of absorption and scattering properties, two runs were conducted: in one run (Case I), the calculated scattering and absorption coefficients were increased proportionally, while in the second run (Case II) only the calculated aerosol scattering coefficient was increased. With the same AOD and extinction profiles, the two runs produce significantly different radiative effects over land and oceans. On the regional mean basis, Case I generates 48 % more heating in the atmosphere and 21 % more dimming at the surface than Case II. Case I also produces stronger cooling responses over the land from the longwave radiation adjustment and boundary layer mixing. These rapid adjustments offset the stronger radiative heating in Case I and lead to an overall lower-troposphere cooling up to −0.7 K day−1, which is smaller than that in Case II. Over the ocean, direct radiative effects dominate the heating rate changes in the lower atmosphere lacking such surface and lower atmosphere adjustments due to fixed sea surface temperature, and the strongest atmospheric warming is obtained in Case I. Consequently, atmospheric dynamics (boundary layer heights and meridional circulation) and thermodynamic processes (water vapor and cloudiness) are shown to respond differently between Case I and Case II underlying the importance of determining the exact portion of scattering or absorbing aerosols that lead to the underestimation of aerosol optical depth in the model. In addition, the model results suggest that both direct radiative effect and rapid thermodynamic responses need to be quantified for understanding aerosol radiative impacts.

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