Intensive Observation Period Research Articles

Local Circulation with Aeolian Dust on the Slopes and Foot Areas of the Tianshan and Kunlun Mountains around the Taklimakan Desert, China

Four automatic weather stations (AWS) were installed on the slopes and foot areas of the Tianshan and Kunlun Mountains along a longitude of 80 degrees east: (1) Taglak 2400 m a.s.l., (2) Aksu 1000 m, (3) Kartash 2800 m, and (4) Qira 1700 m. These two slopes face the Taklimakan Desert. Tagliak lies on the southern slope of Tianshan, and Kartash on the northern slope of Kunlun. The meteorological characteristics of the mountainous regions were investigated using surface data obtained during an intensive observation period (IOP) in spring 2002. It was found that visibility on the slopes decreases in the daytime, and there is no relationship between visibility and wind speed in the mountainous areas. Two snow layers containing dust particles were observed in the snow cover in Taglak during the IOP in spring 2003. These results suggest that a warm air parcel containing aeolian dust climbs over the slopes of the mountainous areas, and dust particles in the mountainous areas are transported from the foot areas.

Bulk Scattering Properties for the Remote Sensing of Ice Clouds. Part II: Narrowband Models

Abstract This study examines the development of bulk single-scattering properties of ice clouds, including single-scattering albedo, asymmetry factor, and phase function, for a set of 1117 particle size distributions obtained from analysis of the First International Satellite Cloud Climatology Project Regional Experiment (FIRE)-I, FIRE-II, Atmospheric Radiation Measurement Program intensive observation period, Tropical Rainfall Measuring Mission Kwajalein Experiment (KWAJEX), and the Cirrus Regional Study of Tropical Anvils and Cirrus Layers (CRYSTAL) Florida Area Cirrus Experiment (FACE) data. The primary focus is to develop band-averaged models appropriate for use by the Moderate Resolution Imaging Spectroradiometer (MODIS) imager on the Earth Observing System Terra and Aqua platforms, specifically for bands located at wavelengths of 0.65, 1.64, 2.13, and 3.75 μm. The results indicate that there are substantial differences in the bulk scattering properties of ice clouds formed in areas of deep convection and those that exist in areas of much lower updraft velocities. Band-averaged bulk scattering property results obtained from a particle-size-dependent mixture of ice crystal habits are compared with those obtained assuming only solid hexagonal columns. The single-scattering albedo is lower for hexagonal columns than for a habit mixture for the 1.64-, 2.13-, and 3.75-μm bands, with the differences increasing with wavelength. In contrast, the asymmetry factors obtained from the habit mixture and only the solid hexagonal column are most different at 0.65 μm, with the differences decreasing as wavelength increases. At 3.75 μm, the asymmetry factor results from the two habit assumptions are almost indistinguishable. The asymmetry factor, single-scattering albedo, and scattering phase functions are also compared with the MODIS version-1 (V1) models. Differences between the current and V1 models can be traced to the microphysical models and specifically to the number of both the smallest and the largest particles assumed in the size distributions.

Estimating the criterion for determining water vapour sources of summer precipitation on the northern Tibetan Plateau

AbstractAccording to the precipitation and δ18O data obtained during the GEWEX Asian Monsoon Experiment–Tibet Intensive Observation Period, based on the knowledge that δ18O is lower in precipitation formed from ocean air mass vapour than that from local evaporation vapour, the water vapour sources can be identified from the δ18O values in precipitation. We attempt to give the identification criterion of δ18O values in precipitation. The threshold values chosen to distinguish between ocean and local sources are δ18O < −20‰ and δ18O > −13‰ respectively. According to this criterion, the proportion of local evaporation‐formed precipitation and ocean air‐mass‐formed precipitation in total precipitation was estimated. The average value of precipitation at three sites (NODA, Amdo and AQB) is 249·76 mm. Among this, precipitation formed directly by the ocean air mass vapour is 80·08 mm at most. Precipitation formed by water vapour evaporated from local places is 117·05 mm at least. That is to say that precipitation formed directly by the ocean air mass vapour accounts for 32·06% of the total precipitation at most. Precipitation formed by water vapour evaporated from local places accounts for 46·86% of the total precipitation at least. At least 21·8% of the total precipitation came from water vapour that was evaporated on the way and transported by the monsoon circulation. Copyright © 2005 John Wiley & Sons, Ltd.

Mesoscale analysis and impact on simulation of IOP14 of the MAP experiment

AbstractThis paper examines the benefit on quantitative precipitation forecasts of assimilating a mesoscale network of surface observations. The analysis is performed with an optimal interpolation system tuned for meso‐β scale (10 km resolution). The case‐study is chosen in the framework of the Mesoscale Alpine Program (MAP). It corresponds to a frontal system crossing France on 2 November 1999 followed by moderate to strong convective activity which developed over the Alps and Italy on 3 November (MAP Intensive Observation Period (IOP) 14).Model sensitivity to the various initial conditions (European Centre for Medium‐Range Weather Forecasts analysis, mesoscale analyses with dense surface observations) and to the resolution (meso‐β versus meso‐γ (2.5 km scale)) is investigated. A comprehensive network of rain‐gauges is used for validation. Conventional objective scores (correlation and equitable threat) are produced for precipitation accumulated over short durations (6 and 1 h) for consistency with the target horizontal scales (meso‐β, meso‐γ). The positive contribution of the surface network to precipitation forecasts is confirmed by a novel and powerful validation method based on the comparison of METEOSAT synthetic radiances (infrared and water vapour channels) computed from the simulations to the corresponding satellite observations. Copyright © 2005 Royal Meteorological Society

Diurnal variation of tropical convection during TOGA COARE IOP

Diurnal variation of tropical convection and kinematic and thermodynamic conditions was investigated for different large-scale environments of the convectively active and inactive periods by using satellite observations and surface measurements during the Intensive Observation Period (IOP) of the Tropical Ocean Global Atmosphere/Coupled Ocean-Atmosphere Response Experiment (TOGA/COARE). During the convectively active period, the features of nocturnal convection appear in vertical profiles of convergence, vertical velocity, heat source, and moisture sink. The specific humidity increases remarkably in the middle troposphere at dawn. On the other hand, the altitude of maximum convergence and that of the upward motion is lower during the convectively inactive period. The specific humidity peaks in the lower troposphere in the daytime and decreases in the middle troposphere. Spectral analyses of the time series of the infrared (IR) brightness temperature (TBB) and amounts of rainfall suggest multiscale temporal variation with a prominent diurnal cycle over land and oceanic regions such as the Intensive Flux Array (IFA) and the South Pacific Convergence Zone (SPCZ). Over land, the daily maximum of deep convection associated with cloud top temperature less than 208 K appears at midnight due to the daytime radiative heating and the sea-land breeze. Over the ocean, convection usually tends to occur at dawn for the convectively active period while in the afternoon during the inactive period. Comparing the diurnal variation of convection with large-scale variables, the authors inferred that moisture in the middle troposphere contributes mostly to the development of nocturnal convection over the ocean during the convectively active period.

Validation of an Urban Surface Exchange Parameterization for Mesoscale Models—1D Case in a Street Canyon

Abstract A detailed urban parameterization scheme is used in and above a street canyon. To validate this new scheme, the model is run offline on a vertical column (one-dimensional simulations), using measurements from a 30-m-high tower for upper boundary conditions. Measurements were obtained during the intensive observation period of the Basel Urban Boundary Layer Experiment (BUBBLE). Vertical profiles of meteorological variables are simulated in the street canyon. The validation of the parameterization is made with measurements from the tower in the street canyon and directly above roof height. The results show that the urban parameterization scheme is able to catch most of the typical processes that are induced by an urban surface near the ground. The fit to measured profiles is improved in comparison with a model using the traditional approach for urban parameterization (variation of z0 to take into account the presence of a city).

Formation Mechanisms for Convection over the Ligurian Sea during MAP IOP-8

Abstract The dynamical impacts of an unusually strong stable layer that developed over the Po Valley and northern Ligurian Sea during Mesoscale Alpine Program (MAP) intensive observation period 8 (IOP-8) on the formation of convection over the Ligurian Sea are explored. Based on numerically simulated equivalent potential temperature, wind vectors, and by a trajectory analysis of parcels both beneath and above the stable layer, it is shown that the stable layer behaved as a material surface or “effective mountain” to the airstreams impinging on it from the south. Additional analyses show that the leading edge of the stable layer was collocated with maxima in upward motion and a strong positive moisture flux. Hence, it was further argued and demonstrated through inspection of soundings upstream of the cold dome and trajectory analyses that lifting by the stable layer enhanced convective activities over the Ligurian Sea. Finally, processes contributing to the maintenance of the stable layer during IOP-8 were explored. It was found that the differential advection of a warm, less stable air mass on top of a cooler, more stable air mass helped maintain the stable layer. The Ligurian Apennines made a secondary contribution to the stagnation of the cool air in the Po Valley by partially blocking this air mass from exiting the valley to the south.

Interrelationship between cloud cover and sensible heat flux over land during MONTBLEX-1990

Micro-meteorological tower observations of MONTBLEX (Monsoon Trough Boundary Layer Experiment)-1990, combined with routine surface observations at Jodhpur in the dry convective sector of Indian summer monsoon trough are used to examine the interrelationship between total cloud cover (TCC) and surface sensible heat flux (SHF) during the summer monsoon of 1990. A significant inverse relationship between TCC and SHF is found during various Intensive Observation Periods of the experiment. This relationship holds for the various methods of estimation of SHF.

Thermodynamic structure of the atmosphere along East coast of India during BOBMEX-99

Thermodynamic features of the Convective Boundary Layer (CBL) during the summer monsoon season of 1999 have been examined over the Indian east coastal stations with respect to the prevailing synoptic scale weather disturbances. For this purpose high resolution aerological observations specially collected during the Bay of Bengal Monsoon Experiment-99 for the Intensive Observing Periods (IOPs) for the six east coastal stations have been considered. Out of the five available IOPs observations during two IOPs, one during July and another during August, 1999, have been used to explore the differences in the CBL characteristics. The coastal stations are categorized into two groups based on the surface pressure distribution and the location of the stations with respect to the prevailing weather disturbance (either deep depression or low pressure area) viz., Gr.A (stations located in the vicinity of the disturbance with low surface pressure) and Gr.B (stations situated away from the disturbance and associated with high surface pressure) stations. The temporal variation of different thermodynamic parameters at the surface indicated more moist convective activity at the surface during August. The averaged vertical profiles of different thermodynamic parameters revealed more convective activity for Gr.A stations as compared to Gr.B stations during both July and August indicating the more influence of the existing disturbance on the stations situated in the proximity of the disturbance. However, the moist convective activity is more during July as compared to August, except in the surface layer, for both the groups. The CBL tops vary in the range 700-500 hPa. The conserved variable diagrams revealed single mixing line structure during both July and August for all the categories.

Evaluation of an Urban Canopy Parameterization in a Mesoscale Model Using VTMX and URBAN 2000 Data

Abstract A modified urban canopy parameterization (UCP) is developed and evaluated in a three-dimensional mesoscale model to assess the urban impact on surface and lower-atmospheric properties. This parameterization accounts for the effects of building drag, turbulent production, radiation balance, anthropogenic heating, and building rooftop heating/cooling. U.S. Geological Survey (USGS) land-use data are also utilized to derive urban infrastructure and urban surface properties needed for driving the UCP. An intensive observational period with clear sky, strong ambient wind, and drainage flow, and the absence of a land–lake breeze over the Salt Lake Valley, occurring on 25–26 October 2000, is selected for this study. A series of sensitivity experiments are performed to gain understanding of the urban impact in the mesoscale model. Results indicate that within the selected urban environment, urban surface characteristics and anthropogenic heating play little role in the formation of the modeled nocturnal urban boundary layer. The rooftop effect appears to be the main contributor to this urban boundary layer. Sensitivity experiments also show that for this weak urban heat island case, the model horizontal grid resolution is important in simulating the elevated inversion layer. The root-mean-square errors of the predicted wind and temperature with respect to surface station measurements exhibit substantially larger discrepancies at the urban locations than their rural counterparts. However, the close agreement of modeled tracer concentration with observations fairly justifies the modeled urban impact on the wind-direction shift and wind-drag effects.

Dynamical controls on sub–global climate model grid‐scale cloud variability for Atmospheric Radiation Measurement Program (ARM) case 4

Global climate models (GCMs) produce large errors in cloudiness and cloud radiative forcing when simulating midlatitude, synoptic‐scale cloud systems. This is because they do not represent the subgrid‐scale processes in these systems that create subgrid variability in cloud optical thickness and cloud top pressure. Improving GCM performance will require a better understanding of these controls on subgrid cloud variability. To begin addressing this issue, this paper uses a mesoscale model, the Regional Atmospheric Modeling System (RAMS), to simulate two case study synoptic storms with much higher resolution than is possible in a GCM. These storms were observed during the Atmospheric Radiation Measurement (ARM) Program's March 2000 Intensive Observing Period (IOP) in the U.S. southern Great Plains (SGP), otherwise knows as ARM case 4. We find that RAMS is able to capture the observed storm morphology, lifecycle, and vertical structure of the atmospheric dynamic and thermodynamic variables. RAMS is also able to capture the observed fine‐scale vertical structure and temporal variation of the cloud field. Given this agreement with observations, we then characterize the model‐simulated variability in cloudiness and other variables such as vertical velocity. In both storms, there is a high degree of spatial and temporal variability in the vertical motion field across multiple scales. The variability in above‐boundary layer cloudiness is closely linked to this dynamical variability. This suggests that a parameterization for subgrid cloud water based on subgrid vertical velocity could be used to improve GCM simulations of midlatitude clouds.

Moisture and temperature balances at the Atmospheric Radiation Measurement Southern Great Plains Site in forecasts with the Community Atmosphere Model (CAM2)

We compare the balance of terms in moisture and temperature prediction equations during short forecasts by the Community Atmosphere Model (CAM2) with observed estimates at the Atmospheric Radiation Measurement (ARM) Southern Great Plains site for two intensive observing periods (IOPs). The goal is to provide insight into parameterization errors which ultimately should lead to model improvements. The atmospheric initial conditions are obtained from high‐resolution numerical weather prediction (NWP) analyses. The land initial conditions are spun up to be consistent with those analyses. Three cases are considered: (1) June/July 1997 when the atmosphere is relatively moist and surface evaporation corresponds to 90% of the precipitation with advection accounting for the remainder; (2) rainy days in April 1997 when the atmosphere is less moist and horizontal advection accounts for much of the precipitation with a small contribution from surface evaporation and the balance being derived from the water already present in the column; and (3) nonrainy days of the April 1997 when the moist process parameterizations are inactive and the planetary boundary layer (PBL) parameterization is dominant. For the first case the Zhang‐McFarlane deep convective parameterization drives the model to a wrong state. For the second the Hack shallow convective parameterization appears to be not acting deep enough. During both periods inconsistencies between CAM2 and ARM surface fluxes, land surface conditions and the net surface radiative fluxes indicate that the exchange parameterizations should be examined further. For the third case the PBL parameterization does not appear to create the correct vertical structure. In addition, the individual components of the dynamical tendency are very different between CAM2 and ARM, although the total dynamical tendency is similar in the two. Although these observations do not imply that those components are themselves wrong since they may be responding to other errors, each of these components should be examined further to determine the cause of their behaviors.

An observational study of soil moisture effects on wind erosion at a gobi site in the Taklimakan Desert

The measurements at a gobi site suggest that (1) saltation mass flux q(z) is particle size and soil moisture‐dependent and (2) a simple relationship exists between q and wind speed u and threshold wind speed ut(θ). The ut(θ) in wet conditions (θ = 0.009 m3 m−3) was estimated to be 9.5 m s−1 at a height of 3.8 m. This value is 1.27 times larger than that in dry condition, which corresponds to Fécan et al.'s theoretical result. The (D) in wet conditions was smaller than that in dry conditions for the particles of 69–203 μm in diameter. However, for 38 and 54 μm particles, the did not change in both dry and wet conditions. Furthermore, long‐term monitoring showed that (1) the ground surface was dry during Aeolian Dust Experiment on Climate Impact (ADEC)‐Intensive Observation Period (IOP) 1 (8–21 April 2002), whereas it was wet during ADEC‐IOP2 (16–27 March 2003) because of snowfall at the beginning of March, and (2) the visibility frequently became worse during warm season when strong winds over the threshold wind speed blew and was dry.

Modeling Diurnal and Intraseasonal Variability of the Ocean Mixed Layer

Abstract The intraseasonal variability of SST associated with the passage of the Madden–Julian oscillation (MJO) is well documented; yet coupled model integrations generally underpredict the magnitude of this SST variability. Observations from the Improved Meteorological Instrument (IMET) mooring in the western Pacific during the intensive observing period (IOP) of the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE) showed a large diurnal signal in SST that is modulated by the passage of the MJO. In this study, observations from the IOP of the TOGA COARE and a one-dimensional (1D) ocean mixed layer model incorporating the K-Profile Parameterization (KPP) vertical mixing scheme have been used to investigate the rectification of the intraseasonal variability of SST by the diurnal cycle and the implied impact of the absence of a representation of this process on the modeled intraseasonal variability in coupled GCMs. Analysis of the SST observations has shown that the increase of the daily mean SST by the diurnal cycle of SST accounts for about one-third of the magnitude of intraseasonal variability of SST associated with the Madden–Julian oscillation in the western Pacific warm pool. Experiments from the 1D model forced with fluxes at a range of temporal resolutions and with differing vertical resolution of the model have shown that to capture 90% of the diurnal variability of SST, and hence 95% of the intraseasonal variability of SST, requires a 3-h or better temporal resolution of the fluxes and a vertical grid with an upper-layer thickness of the order of 1 m. In addition to the impact of the representation of the diurnal cycle on the intraseasonal variability of SST, the strength of the mixing across the thermocline was found to be enhanced by the proper representation of the nighttime deep mixing in the ocean, implying a possible impact of the diurnal cycle onto the mean climate of the tropical ocean.

BUBBLE – an Urban Boundary Layer Meteorology Project

The Basel UrBan Boundary Layer Experiment (BUBBLE) was a year-long experimental effort to investigate in detail the boundary layer structure in the City of Basel, Switzerland. At several sites over different surface types (urban, sub-urban and rural reference) towers up to at least twice the main obstacle height provided turbulence observations at many levels. In addition, a Wind Profiler and a Lidar near the city center were profiling the entire lower troposphere. During an intensive observation period (IOP) of one month duration, several sub-studies on street canyon energetics and satellite ground truth, as well as on urban turbulence and profiling (sodar, RASS, tethered balloon) were performed. Also tracer experiments with near-roof-level release and sampling were performed. In parallel to the experimental activities within BUBBLE, a meso-scale numerical atmospheric model, which contains a surface exchange parameterization, especially designed for urban areas was evaluated and further developed. Finally, the area of the full-scale tracer experiment which also contains several sites of other special projects during the IOP (street canyon energetics, satellite ground truth) is modeled using a very detailed physical scale-model in a wind tunnel. In the present paper details of all these activities are presented together with first results.

Simulations of midlatitude frontal clouds by single‐column and cloud‐resolving models during the Atmospheric Radiation Measurement March 2000 cloud intensive operational period

This study quantitatively evaluates the overall performance of nine single‐column models (SCMs) and four cloud‐resolving models (CRMs) in simulating a strong midlatitude frontal cloud system taken from the spring 2000 Cloud Intensive Observational Period at the Atmospheric Radiation Measurement (ARM) Southern Great Plains site. The evaluation data are an analysis product of constrained variational analysis of the ARM observations and the cloud data collected from the ARM ground active remote sensors (i.e., cloud radar, lidar, and laser ceilometers) and satellite retrievals. Both the selected SCMs and CRMs can typically capture the bulk characteristics of the frontal system and the frontal precipitation. However, there are significant differences in detailed structures of the frontal clouds. Both CRMs and SCMs overestimate high thin cirrus clouds before the main frontal passage. During the passage of a front with strong upward motion, CRMs underestimate middle and low clouds while SCMs overestimate clouds at the levels above 765 hPa. All CRMs and some SCMs also underestimated the middle clouds after the frontal passage. There are also large differences in the model simulations of cloud condensates owing to differences in parameterizations; however, the differences among intercompared models are smaller in the CRMs than the SCMs. In general, the CRM‐simulated cloud water and ice are comparable with observations, while most SCMs underestimated cloud water. SCMs show huge biases varying from large overestimates to equally large underestimates of cloud ice. Many of these model biases could be traced to the lack of subgrid‐scale dynamical structure in the applied forcing fields and the lack of organized mesoscale hydrometeor advections. Other potential reasons for these model errors are also discussed in the paper.

Atmospheric emission inventory of the Maurienne valley for an atmospheric numerical model

Within the framework of an air quality study of the French alpine valleys (POVA program), an atmospheric emission inventory concerning major pollutants: CO, NOx, SO 2, CH 4, particles (PT) and non-methane volatile organic compounds (NMVOC) was carried out. This inventory has a spatial resolution of 1 km 2 and was established for the reference year 2003. The coexistence of economic activities and the Vanoise national park makes the Maurienne valley a sensitive site, particularly representative of the problems of sustainable development in alpine areas, where air pollution is one of the most important aspects. The area, which covers 4588 km 2, is an alpine valley that is sensitive to air pollution due to the emission sources (traffic, industries, private heating, etc.), its morphology (a narrow valley surrounded by high ranges), and local meteorology (temperature inversions and slope winds). As expected, the result which includes both biogenic and anthropogenic sources shows serious emissions of pollutants that are mainly due to the presence of highways and industries around. Two emission inventories were drawn up: one with emission factors determined by CORINAIR (from the European Environment Agency) and the other with emission factors determined by BUWAL-OFEFP (from Swiss Agency for the Environment, Forests and Landscape). The inventories were then compared thanks to concentrations calculated from a numerical model. Computations were run for an intensive field observation period from 25 June to 2 July 2003.

Toward the development of a diffuse horizontal shortwave irradiance working standard

The first intensive observation period (IOP) to simultaneously measure diffuse horizontal shortwave irradiance (scattered solar radiation that falls on a horizontal surface) with a wide array of shaded pyranometers suggested that a consensus might be reached that would permit the establishment of a standard with a smaller uncertainty than previously achieved. A second IOP has been held to refine the first IOP measurements using a uniform calibration protocol, offset corrections for all instruments and validation of those corrections, improvements in some of the instruments, and better data acquisition. The venue for both IOPs was the Department of Energy's Atmospheric Radiation Measurement central facility in northern Oklahoma. The 9 days of measurements in October 2003 included a better mixture of clear and overcast conditions than during the first IOP and revealed considerable differences among the instruments' responses for different cloud conditions. Four of the 15 instruments were eliminated as candidates to be included in the standard because of noisy signals, inadequate offset correction, or instability with respect to the majority of the measurements. Eight pyranometers agreed to within ±2% for clear‐sky conditions. Three others have a high bias on clear days relative to these eight, but all 11 agree within ±2% on overcast days. The differences and causes of this behavior under clear and cloudy skies are examined.

Four-dimensional variational data assimilation experiments for a heavy rain case during the 2002 IOP in China

A heavy rainfall event along the mei-yu front during 22–23 June 2002 was chosen for this study. To assess the impact of the routine and additional IOP (intensive observation period) radiosonde observations on the mesoscale heavy rainfall forecast, a series of four-dimensional variational (4DVAR) data assimilation and model simulation experiments was conducted using nonhydrostatic mesoscale model MM5 and the MM5 4DVAR system. The effects of the intensive observations in the different areas on the heavy rainfall forecast were also investigated. The results showed that improvement of the forecast skill for mesoscale heavy rainfall intensity was possible from the assimilation of the IOP radiosonde observations. However, the impact of the IOP observations on the forecast of the rainfall pattern was not significant. Initial conditions obtained through the 4DVAR experiments with a 12-h assimilation window were capable of improving the 24-h forecast. The simulated results after the assimilation showed that it would be best to perform the intensive radiosonde observations in the upstream of the rainfall area and in the moisture passageway area at the same time. Initial conditions created by the 4DVAR led to the low-level moisture convergence over the rainfall area, enhanced frontogenesis and upward motion within the mei-yu front, and intensified middle- and high-level unstable stratification in front of the mei-yu front. Consequently, the heavy rainfall forecast was improved.

Evaluation of a GCM subgrid cloud‐radiation interaction parameterization using cloud‐resolving model simulations

The mosaic approach of Liang and Wang (1997) for the general circulation model (GCM) parameterization of subgrid cloud‐radiation interactions is evaluated against the validated cloud‐resolving model (CRM) simulation of the Atmospheric Radiation Measurement (ARM) intensive observation period (IOP, June 22–July 17, 1997) at the Southern Great Plains (SGP) site. The CRM‐generated cloud statistics determines the required characteristic structure differences between three primary cloud genera (convective, anvil and stratiform). It is demonstrated that the mosaic approach with the CRM cloud statistics well simulates the CRM domain‐averaged radiative quantities. The result indicates that the mosaic approach of the cloud overlap based on the cloud genera differing in formation mechanisms and of the optical inhomogeneity by cloud water path scaling can capture, respectively, the dominant effects of the cloud geometric association and optical property variability within a GCM grid.