Statistical characteristics of cloud variability. Part 2: Implication for parameterizations of microphysical and radiative transfer processes in climate models

Abstract. Including radiative transfer processes within the urban canopy layer into microscale urban climate models (UCMs) is essential to obtain realistic model results. These processes include the interaction of buildings and vegetation with shortwave and longwave radiation, thermal emission, and radiation reflections. They contribute differently to the radiation budget of urban surfaces. Each process requires different computational resources and physical data for the urban elements. This study investigates how much detail modellers should include to parameterise radiative transfer in microscale building resolving UCMs. To that end, we introduce a stepwise parameterization method to the the PALM model system 6.0 to quantify individually the effects of the main radiative transfer processes on the radiation budget and on the flow field. We quantify numerical simulations of both simple and realistic urban configurations to identify the radiative transfer processes which have major effects on the radiation budget, such as surface and vegetation interaction with short wave and long wave radiation, and those which have minor effects, such as multiple reflections. The study also shows that radiative transfer processes within the canopy layer implicitly affect the incoming radiation since the radiative transfer model is coupled to the radiation model. The flow field changes considerably in response to the radiative transfer processes included in the model. The study highlights those processes which are essentially needed to assure acceptable quality of the flow field. Omitting any of these processes may lead to high uncertainties in the model results.

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Importance of radiative transfer processes in urban climate models: a study based on the PALM 6.0 model system

Geoscientific Model Development ◽

10.5194/gmd-15-145-2022 ◽

2022 ◽

Vol 15 (1) ◽

pp. 145-171

Author(s):

Mohamed H. Salim ◽

Sebastian Schubert ◽

Jaroslav Resler ◽

Pavel Krč ◽

Björn Maronga ◽

...

Keyword(s):

Radiative Transfer ◽

Flow Field ◽

Climate Models ◽

Urban Climate ◽

Longwave Radiation ◽

Radiation Budget ◽

Radiative Transfer Model ◽

Transfer Model ◽

Canopy Layer ◽

Transfer Processes

Abstract. Including radiative transfer processes within the urban canopy layer into microscale urban climate models (UCMs) is essential to obtain realistic model results. These processes include the interaction of buildings and vegetation with shortwave and longwave radiation, thermal emission, and radiation reflections. They contribute differently to the radiation budget of urban surfaces. Each process requires different computational resources and physical data for the urban elements. This study investigates how much detail modellers should include to parameterize radiative transfer in microscale building-resolving UCMs. To that end, we introduce a stepwise parameterization method to the Parallelized Large-eddy Simulation Model (PALM) system 6.0 to quantify individually the effects of the main radiative transfer processes on the radiation budget and on the flow field. We quantify numerical simulations of both simple and realistic urban configurations to identify the major and the minor effects of radiative transfer processes on the radiation budget. The study shows that processes such as surface and vegetation interaction with shortwave and longwave radiation will have major effects, while a process such as multiple reflections will have minor effects. The study also shows that radiative transfer processes within the canopy layer implicitly affect the incoming radiation since the radiative transfer model is coupled to the radiation model. The flow field changes considerably in response to the radiative transfer processes included in the model. The study identified those processes which are essentially needed to assure acceptable quality of the flow field. These processes are receiving radiation from atmosphere based on the sky-view factors, interaction of urban vegetation with radiation, radiative transfer among urban surfaces, and considering at least single reflection of radiation. Omitting any of these processes may lead to high uncertainties in the model results.

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Evaluation of shortwave radiation fluxes in the multi-layer SPARTACUS-Urban scheme using DART

10.5194/egusphere-egu21-16076 ◽

2021 ◽

Author(s):

Megan Stretton ◽

William Morrison ◽

Robin Hogan ◽

Sue Grimmond

Keyword(s):

Radiative Transfer ◽

Urban Form ◽

Climate Models ◽

Weather Prediction ◽

Computational Cost ◽

Three Dimensional ◽

Shortwave Radiation ◽

Radiative Transfer Model ◽

Transfer Model ◽

Urban Structure

The heterogenous structure of cities impacts radiative exchanges (e.g. albedo and heat storage). Numerical weather prediction (NWP) models often characterise the urban structure with an infinite street canyon &#8211; but this does not capture the three-dimensional urban form. SPARTACUS-Urban (SU) - a fast, multi-layer radiative transfer model designed for NWP - is evaluated using the explicit Discrete Anisotropic Radiative Transfer (DART) model for shortwave fluxes across several model domains &#8211; from a regular array of cubes to real cities .SU agrees with DART (errors < 5.5% for all variables) when the SU assumptions of building distribution are fulfilled (e.g. randomly distribution). For real-world areas with pitched roofs, SU underestimates the albedo (< 10%) and shortwave transmission to the surface (< 15%), and overestimates wall-plus-roof absorption (9-27%), with errors increasing with solar zenith angle. SU should be beneficial to weather and climate models, as it allows more realistic urban form (cf. most schemes) without large increases in computational cost.

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Underwater Radiative Transfer Processes

10.1007/978-3-030-63416-2_300205 ◽

2021 ◽

pp. 1302-1302

Keyword(s):

Radiative Transfer ◽

Transfer Processes

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Combined event-based tritium and air mass back-trajectory analysis of Mediterranean precipitation events

10.5194/egusphere-egu2020-8343 ◽

2020 ◽

Author(s):

Tobias Juhlke ◽

Jürgen Sültenfuß ◽

Katja Trachte ◽

Frédéric Huneau ◽

Emilie Garel ◽

...

Keyword(s):

Climate Models ◽

Hydrological Cycle ◽

Early Summer ◽

Water Vapor Transport ◽

Back Trajectory ◽

Data Set ◽

Air Mass ◽

Transfer Processes ◽

Event Based ◽

Precipitation Events

Climate models are in need of improved constraints for water vapor transport in the atmosphere and tritium can serve as a powerful tracer in the hydrological cycle. Although general principles of tritium distribution and transfer processes within and between the various hydrological compartments are known, variation on short timescales and aspects of altitude dependence are still under debate. To address questions for tritium sources, sinks and transfer processes, sampling of individual precipitation events in Corte on the island of Corsica in the Mediterranean Sea was performed between April 2017 and April 2018. Tritium concentrations of 46 event samples were compared to their moisture origin and corresponding air mass history. Air mass back-trajectories were generated from the novel high-resolution ERA 5 data set of the ECMWF (European Centre for Medium-Range Weather Forecasts). Geographical source regions of similar tritium concentrations were predefined using generally known tritium distribution patterns, such as a &#8216;continental effect&#8217;, and from data records derived at long-term measurement stations of tritium in precipitation across the working area. Our model-derived source region tritium concentrations agreed well with annual mean station values. Moisture that originated from continental Europe and the Atlantic Ocean was most distinct regarding tritium concentrations with values up to 8.8 TU and near 0 TU, respectively. Seasonality of tritium values ranged from 1.6 TU in January to 10.1 TU in May and exhibited well-known elevated concentrations in spring and early summer due to increased stratosphere-troposphere exchange. However, this pattern was interrupted by extreme events. The average altitude of trajectories correlated with tritium concentrations in precipitation, especially in spring and early summer and if outlier values of extreme tritium concentrations were excluded. However, in combination with the trajectory information, these outlier values proved to be valuable for the understanding of tritium movement in the atmosphere. Our work shows how event-based tritium research can advance the understanding of its distribution in the atmosphere.

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Evaluation of Cirrus Parameterizations for Radiative Flux Computations in Climate Models Using TOVS–ScaRaB Satellite Observations

Journal of Climate ◽

10.1175/jcli4251.1 ◽

2007 ◽

Vol 20 (17) ◽

pp. 4459-4475 ◽

Cited By ~ 12

Author(s):

C. J. Stubenrauch ◽

F. Eddounia ◽

J. M. Edwards ◽

A. Macke

Keyword(s):

Optical Properties ◽

Radiative Transfer ◽

Climate Models ◽

Radiative Flux ◽

Satellite Observations ◽

Radiation Budget ◽

Radiative Transfer Model ◽

Transfer Model ◽

Ice Crystal ◽

Infrared Observation

Abstract Combined simultaneous satellite observations are used to evaluate the performance of parameterizations of the microphysical and optical properties of cirrus clouds used for radiative flux computations in climate models. Atmospheric and cirrus properties retrieved from Television and Infrared Observation Satellite (TIROS-N) Operational Vertical Sounder (TOVS) observations are given as input to the radiative transfer model developed for the Met Office climate model to simulate radiative fluxes at the top of the atmosphere (TOA). Simulated cirrus shortwave (SW) albedos are then compared to those retrieved from collocated Scanner for Radiation Budget (ScaRaB) observations. For the retrieval, special care has been given to angular direction models. Three parameterizations of cirrus ice crystal optical properties are represented in the Met Office radiative transfer model. These parameterizations are based on different physical approximations and different hypotheses on crystal habit. One parameterization assumes pristine ice crystals and two ice crystal aggregates. By relating the cirrus ice water path (IWP) retrieved from the effective infrared emissivity to the cirrus SW albedo, differences between the parameterizations are amplified. This study shows that pristine crystals seem to be plausible only for cirrus with IWP less than 30 g m−2. For larger IWP, ice crystal aggregates lead to cirrus SW albedos in better agreement with the observations. The data also indicate that climate models should allow the cirrus effective ice crystal diameter (De) to increase with IWP, especially in the range up to 30 g m−2. For cirrus with IWP less than 20 g m−2, this would lead to SW albedos that are about 0.02 higher than the ones of a constant De of 55 μm.

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Mesoscale Simulations of Australian Direct Normal Irradiance, Featuring an Extreme Dust Event

Journal of Applied Meteorology and Climatology ◽

10.1175/jamc-d-17-0091.1 ◽

2018 ◽

Vol 57 (3) ◽

pp. 493-515 ◽

Cited By ~ 7

Author(s):

S. K. Mukkavilli ◽

A. A. Prasad ◽

R. A. Taylor ◽

A. Troccoli ◽

M. J. Kay

Keyword(s):

Radiative Transfer ◽

Climate Models ◽

Global Climate ◽

Weather Prediction ◽

Wrf Model ◽

Global Climate Models ◽

Radiative Transfer Model ◽

Transfer Model ◽

Dust Event ◽

Direct Normal Irradiance

AbstractDirect normal irradiance (DNI) is the main input for concentrating solar power (CSP) technologies—an important component in future energy scenarios. DNI forecast accuracy is sensitive to radiative transfer schemes (RTSs) and microphysics in numerical weather prediction (NWP) models. Additionally, NWP models have large regional aerosol uncertainties. Dust aerosols can significantly attenuate DNI in extreme cases, with marked consequences for applications such as CSP. To date, studies have not compared the skill of different physical parameterization schemes for predicting hourly DNI under varying aerosol conditions over Australia. The authors address this gap by aiming to provide the first Weather and Forecasting (WRF) Model DNI benchmarks for Australia as baselines for assessing future aerosol-assimilated models. Annual and day-ahead simulations against ground measurements at selected sites focusing on an extreme dust event are run. Model biases are assessed for five shortwave RTSs at 30- and 10-km grid resolutions, along with the Thompson aerosol-aware scheme in three different microphysics configurations: no aerosols, fixed optical properties, and monthly climatologies. From the annual simulation, the best schemes were the Rapid Radiative Transfer Model for global climate models (RRTMG), followed by the new Goddard and Dudhia schemes, despite the relative simplicity of the latter. These top three RTSs all had 1.4–70.8 W m−2 lower mean absolute error than persistence. RRTMG with monthly aerosol climatologies was the best combination. The extreme dust event had large DNI mean bias overpredictions (up to 4.6 times), compared to background aerosol results. Dust storm–aware DNI forecasts could benefit from RRTMG with high-resolution aerosol inputs.

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Antarctic Low-Tropospheric Humidity Inversions: 10-Yr Climatology

Journal of Climate ◽

10.1175/jcli-d-12-00446.1 ◽

2013 ◽

Vol 26 (14) ◽

pp. 5205-5219 ◽

Cited By ~ 21

Author(s):

Tiina Nygård ◽

Teresa Valkonen ◽

Timo Vihma

Keyword(s):

Water Vapor ◽

Climate Models ◽

Weather Prediction ◽

Temperature Inversion ◽

Statistical Characteristics ◽

The Arctic ◽

Radiosonde Data ◽

Atmospheric Moisture Budget ◽

Temperature Inversions ◽

The Antarctic

Abstract Humidity inversions are nearly permanently present in the coastal Antarctic atmosphere. This is shown based on an investigation of statistical characteristics of humidity inversions at 11 Antarctic coastal stations using radiosonde data from the Integrated Global Radiosonde Archive (IGRA) from 2000 to 2009. The humidity inversion occurrence was highest in winter and spring, and high atmospheric pressure and cloud-free conditions generally increased the occurrence. A typical humidity inversion was less than 200 m deep and 0.2 g kg−1 strong, and a typical humidity profile contained several separate inversion layers. The inversion base height had notable seasonal variations, but generally the humidity inversions were located at higher altitudes than temperature inversions. Roughly half of the humidity inversions were associated with temperature inversions, especially near the surface, and humidity and temperature inversion strengths as well as depths correlated at several stations. On the other hand, approximately 60% of the humidity inversions were accompanied by horizontal advection of water vapor increasing with height, which is also a probable factor supporting humidity inversions. The spatial variability of humidity inversions was linked to the topography and the water vapor content of the air. Compared to previous results for the Arctic, the most striking differences in humidity inversions in the Antarctic were a much higher frequency of occurrence in summer, at least under clear skies, and a reverse seasonal cycle of the inversion height. The results can be used as a baseline for validation of weather prediction and climate models and for studies addressing changes in atmospheric moisture budget in the Antarctic.

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