Longwave 3D Benchmarks for Inhomogeneous Clouds and Comparisons with Approximate Methods

Kablick, George P.; Ellingson, Robert G.; Takara, E. E.; Gu, Jlujing

doi:10.1175/2010jcli3752.1

Cited by 18 publications

(20 citation statements)

References 30 publications

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“…More recent studies using accurate radiative transfer models (e.g., Monte Carlo models) found strong 3-D local thermal cooling rates reaching up to 300-600 K day −1 (e.g., Kablick et al, 2011;Klinger and Mayer, 2014) in realistic 3-D cloud field simulations. It was shown that 3-D cooling rates exceed 1-D cooling rates both in magnitude and by an additional cloud side cooling.…”

Section: Introductionmentioning

confidence: 99%

Effects of 3-D thermal radiation on the development of a shallow cumulus cloud field

et al. 2017

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Abstract. We investigate the effects of thermal radiation on cloud development in large-eddy simulations (LESs) with the UCLA-LES model. We investigate single convective clouds (driven by a warm bubble) at 50 m horizontal resolution and a large cumulus cloud field at 50 and 100 m horizontal resolutions. We compare the newly developed 3-D Neighboring Column Approximation with the independent column approximation and a simulation without radiation and their respective impact on clouds. Thermal radiation causes strong local cooling at cloud tops accompanied by a modest warming at the cloud bottom and, in the case of the 3-D scheme, also cloud side cooling. 3-D thermal radiation causes systematically larger cooling when averaged over the model domain. In order to investigate the effects of local cooling on the clouds and to separate these local effects from a systematically larger cooling effect in the modeling domain, we apply the radiative transfer solutions in different ways. The direct effect of heating and cooling at the clouds is applied (local thermal radiation) in a first simulation. Furthermore, a horizontal average of the 1-D and 3-D radiation in each layer is used to study the effect of local cloud radiation as opposed to the domain-averaged effect. These averaged radiation simulations exhibit a cooling profile with stronger cooling in the cloudy layers. In a final setup, we replace the radiation simulation by a uniform cooling of 2.6 K day −1 . To focus on the radiation effects themselves and to avoid possible feedbacks, we fixed surface fluxes of latent and sensible heat and omitted the formation of rain in our simulations.Local thermal radiation changes cloud circulation in the single cloud simulations, as well as in the shallow cumulus cloud field, by causing stronger updrafts and stronger subsiding shells. In our cumulus cloud field simulation, we find that local radiation enhances the circulation compared to the averaged radiation applications. In addition, we find that thermal radiation triggers the organization of clouds in two different ways. First, local interactive radiation leads to the formation of cell structures; later on, larger clouds develop. Comparing the effects of 3-D and 1-D thermal radiation, we find that organization effects of 3-D local thermal radiation are usually stronger than the 1-D counterpart. Horizontally averaged radiation causes more clouds and deeper clouds than a no radiation simulation but, in general less-organized clouds than in the local radiation simulations. Applying a constant cooling to the simulations leads to a similar development of the cloud field as in the case of averaged radiation, but less water condenses overall in the simulation. Generally, clouds contain more liquid water if radiation is accounted for. Furthermore, thermal radiation enhances turbulence and mixing as well as the size and lifetime of clouds. Local thermal radiation produces larger clouds with longer lifetimes.The cloud fields in the 100 and 50 m resolution simulations develop similarly...

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Section: Introductionmentioning

confidence: 99%

Effects of 3-D thermal radiation on the development of a shallow cumulus cloud field

et al. 2017

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“…At SZAs larger than 60 • , however, the so-called "elongated shadow effect" (Wissmeier et al, 2013), which is generally present for all Sun positions except for overhead Sun, becomes dominant and solar net surface flux in the ICA experiment is overestimated relative to 3-D. This is essentially the cloud side illumination effect, where the effective total cloud cover (Di Giuseppe and Tompkins, 2003;Tompkins and Di Giuseppe, 2007;Hinkelman et al, 2007) increases with descending Sun, and hence also the size of the shadow increases with decreasing solar elevation, which is not taken into account in the ICA. This leads to a considerably reduced direct radiation reaching the ground and thus solar net flux in the 3-D experiment when the Sun is lower in the sky.…”

Section: Net Surface Fluxmentioning

confidence: 95%

“…The background profiles of atmospheric pressure, temperature, density and trace gases (water vapor, O 3 , CO 2 ) were taken from the US standard atmosphere (Anderson et al, 1986) and are horizontally homogeneous across the domain. Parameterization of absorption and scattering properties of the atmosphere in the solar part of the spectrum follows the correlated-k distribution of Kato et al (1999). Parameterization of molecular absorption in the thermal spectral range was adopted from Fu and Liou (1992).…”

Section: Radiative Transfer Computations -Model Setupmentioning

confidence: 99%

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Quantifying the bias of radiative heating rates in numerical weather prediction models for shallow cumulus clouds

Črnivec

Mayer

2019

Atmos. Chem. Phys.

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Abstract. The interaction between radiation and clouds represents a source of uncertainty in numerical weather prediction (NWP) due to both intrinsic problems of one-dimensional radiation schemes and poor representation of clouds. The underlying question addressed in this study is how large the NWP radiative bias is for shallow cumulus clouds and how it scales with various input parameters of radiation schemes, such as solar zenith angle, surface albedo, cloud cover and liquid water path. A set of radiative transfer calculations was carried out for a realistically evolving shallow cumulus cloud field stemming from a large-eddy simulation (LES). The benchmark experiments were performed on the highly resolved LES cloud scenes (25 m grid spacing) using a three-dimensional Monte Carlo radiation model. An absence of middle and high clouds is assumed above the shallow cumulus cloud layer. In order to imitate the poor representation of shallow cumulus in NWP models, cloud optical properties were horizontally averaged over the cloudy part of the boxes with dimensions comparable to NWP horizontal grid spacing (several kilometers), and the common δ-Eddington two-stream method with maximum-random overlap assumption for partial cloudiness was applied (denoted as the “1-D” experiment). The bias of the 1-D experiment relative to the benchmark was investigated in the solar and thermal parts of the spectrum, examining the vertical profile of heating rate within the cloud layer and the net surface flux. It is found that, during daytime and nighttime, the destabilization of the cloud layer in the benchmark experiment is artificially enhanced by an overestimation of the cooling at cloud top and an overestimation of the warming at cloud bottom in the 1-D experiment (a bias of about −15 K d−1 is observed locally for stratocumulus scenarios). This destabilization, driven by the thermal radiation, is maximized during nighttime, since during daytime the solar radiation has a stabilizing tendency. The daytime bias at the surface is governed by the solar fluxes, where the 1-D solar net flux overestimates (underestimates) the corresponding benchmark at low (high) Sun. The overestimation at low Sun (bias up to 80 % over land and ocean) is largest at intermediate cloud cover, while the underestimation at high Sun (bias up to −40 % over land and ocean) peaks at larger cloud cover (80 % and beyond). At nighttime, the 1-D experiment overestimates the amount of benchmark surface cooling with the maximal bias of about 50 % peaked at intermediate cloud cover. Moreover, an additional experiment was carried out by running the Monte Carlo radiation model in the independent column mode on cloud scenes preserving their LES structure (denoted as the “ICA” experiment). The ICA is clearly more accurate than the 1-D experiment (with respect to the same benchmark). This highlights the importance of an improved representation of clouds even at the resolution of today's regional (limited-area) numerical models, which needs to be considered if NWP radiative biases are to be efficiently reduced. All in all, this paper provides a systematic documentation of NWP radiative biases, which is a necessary first step towards an improved treatment of radiation–cloud interaction in atmospheric models.

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“…This horizontal transport of radiation causes enhanced cloud top cooling and additional cloud side cooling, so‐called 3D effects, in the thermal spectral range. These 3D thermal heating rates can be as high as several hundred K day

^{- 1}

(Kablick et al, ; Klinger & Mayer, ) and have been shown to modify cloud circulation and cloud field organization (Guan et al, ; Klinger et al, , ) of shallow cumulus clouds.…”

Section: Introductionmentioning

confidence: 99%

Neighboring Column Approximation—An Improved 3D Thermal Radiative Transfer Approximation for Non‐Rectangular Grids

Klinger

Mayer

2020

J Adv Model Earth Syst

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We present a significantly improved version of the Neighboring Column Approximation (NCA 2.0), a fast 3D approximation for the calculation of thermal heating and cooling rates in cloudy atmospheres for large eddy simulation models. The method can now be used on non-rectangular grids, and the heating rate bias in cloudy atmospheres is substantially reduced compared to a 1D solution and the original version of the NCA (NCA 1.0). For different cloud fields the bias is in the range of −5-30% in the 1D case and −2-7% for the NCA 2.0. The calculation of 3D radiative transfer quantities requires horizontal transport of radiation which causes difficulties in the parallelization of numerical models and is computationally expensive. The NCA overcomes this problem and can calculate 3D thermal heating rates at the expense of only a factor 1.5 to 2 higher compared to a 1D radiative transfer approximation. The method uses the fluxes calculated by a 1D radiation scheme and estimates horizontal fluxes using results from neighboring columns. For the estimation of the heating rates from the before estimated fluxes pre-calculated lookup tables of emissivities are used. For the calculation of the heating rates we neglect scattering (independent of the fact if the incoming fluxes consider scattering or not). Inconsistencies made by assumptions for the method are corrected by a correction factor. Plain Language Summary Radiation drives weather and climate of our planet. Yet radiative transfer is treated poorly in most atmospheric models. A common way to treat radiative transfer in atmospheric models is a so-called independent column approximation. However, this method is known to introduce biases. Especially in today's high-resolution large eddy simulations models, 3D radiative effects become more and more important. This work describes a new and fast approach (Neighboring Column Approximation, NCA) which allows calculating 3D heating and cooling rates in the thermal spectral range in large eddy simulation models. Compared to the previously described method, the new one can also be used on non-rectangular grid, as for example a triangular grid, and it improved in speed and accuracy.

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Longwave 3D Benchmarks for Inhomogeneous Clouds and Comparisons with Approximate Methods

Cited by 18 publications

References 30 publications

Effects of 3-D thermal radiation on the development of a shallow cumulus cloud field

Effects of 3-D thermal radiation on the development of a shallow cumulus cloud field

Quantifying the bias of radiative heating rates in numerical weather prediction models for shallow cumulus clouds

Neighboring Column Approximation—An Improved 3D Thermal Radiative Transfer Approximation for Non‐Rectangular Grids

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