Search

This paper introduces the aerosol, clouds, convection and precipitation (ACCP) program that is currently in the process of defining a number of measurement objectives for NASA that are to be implemented toward the end of the current decade. Since a (solar) visible-shortwave infrared (VSWIR) spectrometer is being considered as part of the ACCP architecture, illustrations of the different ways these measurements will contribute to this program and how these measurements can be expected to advance the science objectives of ACCP are highlighted. These contributions range from 1) constraining cloud radiative process and related estimates of radiative fluxes, 2) scene discrimination, 3) providing aerosol and cloud optical properties, and 4) providing other enhanced information such as the phase of water in clouds, and total column water vapor. The spectral measurements also offer new capabilities that will further enhance the ACCP science such as the discrimination of dust aerosol and the potential for the vertical profiling cloud droplet size in shallow clouds. The areas where the maturity of approaches is lacking is also highlighted as a way of emphasizing research topics to be a focus in the coming years.

Most of the global climate models (GCMs) in the Coupled Model Intercomparison Project, phase 5 do not include precipitating ice (aka falling snow) in their radiation calculations. We examine the importance of the radiative effects of precipitating ice on simulated surface wind stress and sea surface temperatures (SSTs) in terms of seasonal variation and in the evolution of central Pacific El Niño (CP‐El Niño) events. Using controlled simulations with the CESM1 model, we show that the exclusion of precipitating ice radiative effects generates a persistent excessive upper‐level radiative cooling and an increasingly unstable atmosphere over convective regions such as the western Pacific and tropical convergence zones. The invigorated convection leads to persistent anomalous low‐level outflows which weaken the easterly trade winds, reducing upper‐ocean mixing and leading to a positive SST bias in the model mean state. In CP‐El Niño events, this means that outflow from the modeled convection in the central Pacific reduces winds to the east, allowing unrealistic eastward propagation of warm SST anomalies following the peak in CP‐El Niño activity. Including the radiative effects of precipitating ice reduces these model biases and improves the simulated life cycle of the CP‐El Niño. Improved simulations of present‐day tropical seasonal variations and CP‐El Niño events would increase the confidence in simulating their future behavior.

Land skin temperature (Ts) is directly influenced by surface energy balance, in particular, radiative energy, which can be linked to model’s representation of radiative effects of hydrometeors in the atmosphere. This link is inferred by examining the changes of geographical distribution and seasonal cycle of surface radiation, surface turbulent fluxes and Ts between a pair of 140 years sensitivity experiments under 1% per year increase of atmospheric CO2. One is with radiative effects of falling ice (snow) hydrometeors on (SON) and the other off (NOS) using CESM1-CAM5 and the results are compared with CMIP5 models without these effects. For boreal winter, NOS relative to SON simulates less surface downward longwave and net flux (∼10–15 W m−2), resulting in colder Ts (∼2–3 K colder), over mid- and high latitudes, but more solar radiative flux, resulting in warmer Ts (∼1–3 K), over subtropical and tropical land. These differences between NOS and SON are amplified as the surface and the atmosphere become warmer. The results from CMIP5 ensemble generally match with those of NOS. Temporal correlation analysis indicates that the linkage between Ts and falling ice hydrometeor changes is through one between Ts and downward longwave and net fluxes at high latitudes, but strongly weakened by shortwave changes at low latitudes (and boreal summer). Relative to SON, land skin temperatures in NOS and CMIP5 are underestimated throughout the seasonal cycle but only slightly in summer.

Clouds play a crucial role in Earth's radiative budget, yet their climate feedbacks are poorly understood. The advent of space-borne high resolution spectrometers probing the O2 A band, like GOSAT and OCO-2, could make it possible to simultaneously retrieve vertically resolved cloud parameters that play a vital role in Earth's radiative budget, thereby allowing a reduction of the corresponding uncertainty due to clouds. Such retrievals would also facilitate air mass bias reduction in corresponding measurements of CO2 columns. In this work, the hyperspectral, polarimetric response of the O2 A band to mainly three important cloud parameters, viz., optical thickness, top height and droplet size has been studied, revealing a different sensitivity to each for the varying atmospheric absorption strength within the A band. Cloud optical thickness finds greatest sensitivity in intensity measurements, the sensitivity of other Stokes parameters being limited to low cloud optical thicknesses. Cloud height had a negligible effect on intensity measurements at non-absorbing wavelengths but finds maximum sensitivity at an intermediate absorption strength, which increases with cloud height. The same is found to hold for cloud geometric thickness. The geometry-dependent sensitivity to droplet size is maximum at non-absorbing wavelengths and diminishes with increasing absorption strength. It has been shown that significantly more information on droplet size can be drawn from multi-angle measurements. We find that, in the absence of sunglint, the backscatter hemisphere (scattering angle larger than 90°) is richer in information on droplet size, especially in the glory and rainbow regions. It has been shown that I and Q generally have differing sensitivities to all cloud parameters. Thus, accurate measurements of two orthogonal components IP andIS (as in GOSAT) are expected to contain more information than measurements of only I, Ih or Iv (as in the case of OCO-2).

In the presence of aerosol and/or clouds, the use of appropriate truncation methods becomes indispensable for accurate but cost-efficient radiative transfer computations. Truncation methods allow the reduction of the large number (usually several hundreds) of Fourier components associated with particulate scattering functions to a more manageable number, thereby making it possible to carry out radiative transfer computations with a modest number of streams. While several truncation methods have been discussed for scalar radiative transfer, few rigorous studies have been made of truncation methods for the vector case. Here, we formally derive the vector form of Wiscombe׳s delta-m truncation method. Two main sources of error associated with delta-m truncation are identified as the delta-separation error (DSE) and the phase-truncation error (PTE). The view angles most affected by truncation error occur in the vicinity of the direction of exact backscatter. This view geometry occurs commonly in satellite based remote sensing applications, and is hence of considerable importance. In order to deal with these errors, we adapt the δ-fit approach of Hu et al. (2000) [17] to vector radiative transfer. The resulting δBGE-fit is compared with the vectorized delta-m method. For truncation at l=25 of an original phase matrix consisting of over 300 Fourier components, the use of the δBGE-fit minimizes the error due to truncation at these view angles, while practically eliminating error at other angles. We also show how truncation errors have a distorting effect on hyperspectral absorption line shapes. The choice of the δBGE-fit method over delta-m truncation minimizes errors in absorption line depths, thus affording greater accuracy for sensitive retrievals such as those of XCO2 from OCO-2 or GOSAT measurements.

Southern Ocean sea-ice cover exerts critical control on local albedo and Antarctic precipitation, but simulated Antarctic sea-ice concentration commonly disagrees with observations. Here we show that the radiative effects of precipitating ice (falling snow) contribute substantially to this discrepancy. Many models exclude these radiative effects, so they underestimate both shortwave albedo and downward longwave radiation. Using two simulations with the climate model CESM1, we show that including falling-snow radiative effects improves the simulations relative to cloud properties from CloudSat-CALIPSO, radiation from CERES-EBAF and sea-ice concentration from passive microwave sensors. From 50–70°S, the simulated sea-ice-area bias is reduced by 2.12 × 106 km2 (55%) in winter and by 1.17 × 106 km2 (39%) in summer, mainly because increased wintertime longwave heating restricts sea-ice growth and so reduces summer albedo. Improved Antarctic sea-ice simulations will increase confidence in projected Antarctic sea level contributions and changes in global warming driven by long-term changes in Southern Ocean feedbacks.

Global weather and climate models often exclude the effects of precipitating hydrometeors and convective core mass on radiative fluxes. In particular, many models split the ice phase into separate “cloud ice” and “snow” categories representing the smaller and larger ice particles, respectively; a separation that is generally not well defined in observations. A version of the European Centre for Medium-Range Weather Forecasts (ECMWF) global numerical weather prediction model which includes the radiative effects of cloud liquid, cloud ice, and precipitating snow is used to investigate the impact of including and excluding the radiative effects of the precipitating snow category. The results show that exclusion of precipitating snow in the radiation calculations leads to differences in the shortwave and longwave radiative fluxes of 5–15 W m−2 in strongly precipitating and convective areas. These differences are of the same order of magnitude as the systematic errors in the model compared to satellite observations. Corresponding biases in the radiative heating profiles are on the order of 0.15 K d−1. The results imply that precipitating snow should be included in the radiative calculations in all weather and climate models in the context of improving model fidelity and reducing compensating errors.

Observations from multiple satellites and large-eddy simulations (LESs) from the Regional Atmospheric Modeling System (RAMS) are used to determine the extent to which free-tropospheric clouds (FTCs) affect the properties of stratocumulus. Overlying FTCs decrease the cloud-top radiative cooling in stratocumulus by an amount that depends on the upper-cloud base altitude, cloud optical thickness, and abundance of moisture between the cloud layers. On average, FTCs increase the downward longwave radiative flux above stratocumulus clouds (at 3.5 km) by approximately 30 W m−2. As a consequence, this forcing translates to a relative decrease in stratocumulus cooling rates by about 20%. Overall, the reduced cloud-top radiative cooling decreases the turbulent mixing, vertical development, and precipitation rate in stratocumulus clouds at night. During the day these effects are greatly reduced because the overlying clouds shade the stratocumulus from strong solar radiation, thus reducing the net radiative effect by the upper cloud. Differences in liquid water path are also observed in stratocumulus; however, the response is tied to the diurnal cycle and the time scale of interaction between the FTCs and the stratocumulus. Radiative effects by FTCs tend to be largest in the midlatitudes where the clouds overlying stratocumulus tend to be more frequent, lower, and thicker on average. In conclusion, changes in net radiation and moisture brought about by FTCs can significantly affect the dynamics of marine stratocumulus and these processes should be considered when evaluating cloud feedbacks in the climate system.

[1] We evaluate the annual mean radiative shortwave flux downward at the surface (RSDS) and reflected shortwave (RSUT) and radiative longwave flux upward at top of atmosphere (RLUT) from the twentieth century Coupled Model Intercomparison Project Phase 5 (CMIP5) and Phase 3 (CMIP3) simulations as well as from the NASA GEOS5 model and Modern-Era Retrospective Analysis for Research and Applications analysis. The results show that a majority of the models have significant regional biases in the annual means of RSDS, RLUT, and RSUT, with biases from −30 to 30 W m−2. While the global average CMIP5 ensemble mean biases of RSDS, RLUT, and RSUT are reduced compared to CMIP3 by about 32% (e.g., −6.9 to 2.5 W m−2), 43%, and 56%, respectively. This reduction arises from a more complete cancellation of the pervasive negative biases over ocean and newly larger positive biases over land. In fact, based on these biases in the annual mean, Taylor diagram metrics, and RMSE, there is virtually no progress in the simulation fidelity of RSDS, RLUT, and RSUT fluxes from CMIP3 to CMIP5. A persistent systematic bias in CMIP3 and CMIP5 is the underestimation of RSUT and overestimation of RSDS and RLUT in the convectively active regions of the tropics. The amount of total ice and liquid atmospheric water content in these areas is also underestimated. We hypothesize that at least a part of these persistent biases stem from the common global climate model practice of ignoring the effects of precipitating and/or convective core ice and liquid in their radiation calculations.

The launch of CloudSat and Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) in 2006 provided the first opportunity to incorporate information about the vertical distribution of cloud and aerosols directly into global estimates of atmospheric radiative heating. Vertical profiles of radar and lidar backscatter from CloudSat’s Cloud Profiling Radar (CPR) and the Cloud–Aerosol Lidar with Orthogonal Polarization (CALIOP) aboard CALIPSO naturally complement Moderate Resolution Imaging Spectroradiometer (MODIS) radiance measurements, providing a nearly complete depiction of the cloud and aerosol properties that are essential for deriving high-vertical-resolution profiles of longwave (LW) and shortwave (SW) radiative fluxes and heating rates throughout the atmosphere. This study describes a new approach for combining vertical cloud and aerosol information from CloudSat and CALIPSO with MODIS data to assess impacts of clouds and aerosols on top-of-atmosphere (TOA) and surface radiative fluxes. The resulting multisensor cloud–aerosol product is used to document seasonal and annual mean distributions of cloud and aerosol forcing globally from June 2006 through April 2011. Direct comparisons with Clouds and the Earth’s Radiant Energy System (CERES) TOA fluxes exhibit a close correlation, with improved errors relative to CloudSat-only products. Sensitivity studies suggest that remaining uncertainties in SW fluxes are dominated by uncertainties in CloudSat liquid water content estimates and that the largest sources of LW flux uncertainty are prescribed surface temperature and lower-tropospheric humidity. Globally and annually averaged net TOA cloud radiative effect is found to be −18.1 W m−2. The global, annual mean aerosol direct radiative effect is found to be −1.6 ± 0.5 W m−2 (−2.5 ± 0.8 W m−2 if only clear skies over the ocean are considered), which, surprisingly, is more consistent with past modeling studies than with observational estimates that were based on passive sensors.

The impacts of enhanced aerosol concentrations such as those associated with dust intrusions on the trimodal distribution of tropical convection have been investigated through the use of large-domain (10 000 grid points), fine-resolution (1 km), long-duration (100 days), two-dimensional idealized cloud-resolving model simulations conducted under conditions of radiative–convective equilibrium (RCE). The focus of this research is on those aerosols that serve primarily as cloud condensation nuclei (CCN). The results demonstrate that the large-scale organization of convection, the domain-averaged precipitation, and the total cloud fraction show only show a weak response to enhanced aerosol concentrations. However, while the domainwide responses to enhanced aerosol concentrations are weak, aerosol indirect effects on the three tropical cloud modes are found to be quite significant and often opposite in sign, a fact that appears to contribute to the weaker domain response. The results suggest that aerosol indirect effects associated with shallow clouds may offset or compensate for the aerosol indirect effects associated with congestus and deep convection systems and vice versa, thus producing a more moderate domainwide response to aerosol indirect forcing. Finally, when assessing the impacts of aerosol indirect forcing associated with CCN on the characteristics of tropical convection, several aspects need to be considered, including which cloud mode or type is being investigated, the field of interest, and whether localized or systemwide responses are being examined.

This study examines the sensitivity of the retrieved cloud droplet radii (CDR) to the vertical inhomogeneity of droplet radii, including the existence of a drizzle mode in clouds. The focus of this study is warm water-phase clouds. Radiative transfer simulations of three near-infrared Moderate Resolution Imaging Spectroradiometer (MODIS) channels centered on wavelengths of 1.6, 2.1, and 3.7 μm reveal that the retrieved CDR are strongly influenced by the vertical inhomogeneity of droplet size including (i) the existence of small cloud droplets at the cloud top and (ii) the existence of the drizzle mode. The influence of smaller droplets at cloud top affects the 3.7-μm channel most, whereas the presence of drizzle influences radiances of both the 2.1- and 1.6-μm channels more than the 3.7-μm channel. Differences in the CDR obtained from MODIS 1.6-, 2.1-, and 3.7-μm channels that appear in global analysis of MODIS retrievals and the CDR derived from data collected during the First International Satellite Cloud Climatology Project (ISCCP) Regional Experiment (FIRE) intensive observation period in 1987 can be explained by the results obtained from the sensitivity experiments of this study.

Anomalies of precipitation, cloud, thermodynamic, and radiation variables are analyzed on the large spatial scale defined by the tropical oceans. In particular, relationships between the mean tropical oceanic precipitation anomaly and radiative anomalies are examined. It is found that tropical mean precipitation is well correlated with cloud properties and radiative fields. In particular, the tropical mean precipitation anomaly is positively correlated with the top of the atmosphere reflected shortwave anomaly and negatively correlated with the emitted longwave anomaly. The tropical mean relationships are found to primarily result from a coherent oscillation of precipitation and the area of high-level cloudiness. The correlations manifest themselves radiatively as a modest decrease in net downwelling radiation at the top of the atmosphere, and a redistribution of energy from the surface to the atmosphere through reduced solar radiation to the surface and decreased longwave emission to space. Integrated over the tropical oceanic domain, the anomalous atmospheric column radiative heating is found to be about 10% of the magnitude of the anomalous latent heating. The temporal signature of the radiative heating is observed in the column mean temperature that indicates a coherent phase-lagged oscillation between atmospheric stability and convection. These relationships are identified as a radiative–convective cloud feedback that is observed on intraseasonal time scales in the tropical atmosphere.

Observations by Johnson et al. depict regions of active tropical convection as possessing increased relative humidity through a deep layer and reduced low-level static stability when compared to nonconvecting regions. Shallow cumulus clouds, congestus clouds, and deep convection all coexist within these convecting regions. This investigation explores the effect that radiation might have on the tropical cloud distributions by using large-domain (20 000 km) radiative–convective equilibrium cloud-resolving model (RCE-CRM) experiments that reproduce similar moisture, stability, and cloud structures to those observed. Radiation is found to significantly increase the amount of shallow and intermediate-level clouds (tops between 1.5 and 5 km) by increasing low-level stability and thus promoting additional low-level cloud detrainment. The mechanism by which radiation stabilizes the low levels is found to differ between convectively suppressed and active regions. In convectively suppressed regions, strong relative humidity gradients within the trade inversion layer produce a low-level cooling maximum that further stabilizes the stable layer, much as proposed by Mapes and Zuidema. In convectively active regions, sufficiently moist columns with no relative humidity gradients are also found to produce a low-level cooling maximum that stabilizes the lower levels. This cooling maximum is due to the complicated effects of the water vapor continuum and is sensitive to the absolute moisture path. Because of the dependence on absolute moisture, the radiative enhancement of shallow and intermediate-level clouds in convectively active regions is potentially sensitive to SSTs.

This paper examines feedbacks between the radiative heating of clouds and convection in the context of numerical radiative–convective equilibrium experiments conducted using both 2D and 3D versions of a cloud-resolving model. The experiments are conducted on a large domain, and equilibria develop as juxtaposed regions of dry and moist air that are connected and sustained by circulations between them. The scales of such variability are large and differ significantly between the 2D and 3D versions of the experiments. Three sensitivity experiments were conducted which, when compared to the control experiment, provide insight into the relative influences of cloud–radiation feedback mechanisms on the equilibrium state achieved. It emerges from the experiments conducted that radiation feedbacks operate via two main pathways, with the radiative heating by high clouds being the governing process of both. The predominant bimodal nature of the moist equilibrium is established by gradients in radiative heating that, in turn, are determined by high cloud differences between wet and dry regions that, in turn, are controlled by convection. Convection, on the other hand, is also influenced by the localized effects of cloud radiative heating by these extended layers of high clouds. The results of the experiments demonstrate how high cloud radiative heating, which is a by-product of the convection itself, provides a feedback that acts to regulate the high clouds produced in the wet convective areas of the equilibrium.

We present an accurate and numerically efficient procedure of calculating Jacobians by finite difference that consists of two components: (1) a method employing the saving of atmospheric layers that accelerates the solution to the equation of radiative transfer for solvers that use the Discrete Space formulation and (2) a method of perturbing the eigenmatrix spectrum associated with a reduced attenuation matrix. The procedure eliminates the need to call the eigenmatrix package, here, LAPACK a second time and provides insights into the fundamental properties of the attenuation matrix, useful for characterizing the accuracy of the derivatives calculated by finite difference methods. The computational complexity of the perturbation method is 8 n 3 + 22 n 2 , where n is one half the number of streams in the radiance field as opposed to 16 n 3 using LAPACK. The method is not limited to the calculation of base state radiances I ( ω ) and those associated with an ‘infinitesimal’ perturbation I ( ω + δ ω ) (from which the numerical derivative of I ( ω + δ ω ) with respect to δ ω may be approximated), but is also useful in the calculation of radiances associated with a ‘finite’ perturbation I ( ω + Δ ω ) from which a sensitivity can be calculated.

The importance of accurately representing the role of clouds in climate change studies has become increasingly apparent in recent years, leading to a substantial increase in the number of satellite sensors and associated algorithms that are devoted to measuring the global distribution of cloud properties. The physics governing the radiative transfer through clouds is well understood, but the impact of uncertainties in algorithm assumptions and the true information content of the measurements in the inverse retrieval problem are generally not as clear, making it difficult to determine the best product to adopt for any particular application. This paper applies information theory to objectively analyze the problem of liquid cloud retrievals from an observing system modeled after the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument currently operating on the Aqua and Terra platforms. It is found that four diagnostics—the retrieval error covariance, the information content, the number of degrees of freedom for signal, and the effective rank of the problem—provide a rigorous test of an observing system. Based on these diagnostics, the combination of the 0.64- and 1.64-μm channels during the daytime and the 3.75- and 11.0-μm channels at night provides the most information for retrieving the properties of the wide variety of liquid clouds modeled. With an eye toward developing a coherent representation of the global distribution of cloud microphysical and radiative properties, these four channels may be integrated into a suitable multichannel inversion methodology such as the optimal estimation or Bayesian techniques to provide a common framework for cloud retrievals under varying conditions. The expected resolution of the observing system for such liquid cloud microphysical property retrievals over a wide variety of liquid cloud is also explored.

The role of horizontal inhomogeneity in radiative transfer through cloud fields is investigated within the context of the two-stream approximation. Spatial correlations between cloud optical properties and the radiance field are introduced in the three-dimensional radiative transfer equation and lead to a two-stream model in which the correlations are represented by parameterizations. The behavior of the model is examined using simple single-layer single-column atmospheres. Positive correlations between extinction or scattering and the radiance field are shown to decrease transmission, increase reflection, and increase absorption within inhomogeneous media. The parameterization is used to evaluate the characteristics of inhomogeneous cloud fields observed by radar and lidar over a number of different locations and seasons, revealing that shortwave transfer is generally characterized by negative correlations between extinction and radiance, while longwave transfer is characterized by positive correlations. The results from this characterization are applied to the integration of an atmospheric general circulation model. Model surface temperatures are significantly affected, largely in response to changes in downwelling radiative fluxes at the surface induced by changes in cloud cover and water vapor distributions.

This paper offers a critical review of the topic of cloud–climate feedbacks and exposes some of the underlying reasons for the inherent lack of understanding of these feedbacks and why progress might be expected on this important climate problem in the coming decade. Although many processes and related parameters come under the influence of clouds, it is argued that atmospheric processes fundamentally govern the cloud feedbacks via the relationship between the atmospheric circulations, cloudiness, and the radiative and latent heating of the atmosphere. It is also shown how perturbations to the atmospheric radiation budget that are induced by cloud changes in response to climate forcing dictate the eventual response of the global-mean hydrological cycle of the climate model to climate forcing. This suggests that cloud feedbacks are likely to control the bulk precipitation efficiency and associated responses of the planet’s hydrological cycle to climate radiative forcings. The paper provides a brief overview of the effects of clouds on the radiation budget of the earth–atmosphere system and a review of cloud feedbacks as they have been defined in simple systems, one being a system in radiative–convective equilibrium (RCE) and others relating to simple feedback ideas that regulate tropical SSTs. The systems perspective is reviewed as it has served as the basis for most feedback analyses. What emerges is the importance of being clear about the definition of the system. It is shown how different assumptions about the system produce very different conclusions about the magnitude and sign of feedbacks. Much more diligence is called for in terms of defining the system and justifying assumptions. In principle, there is also neither any theoretical basis to justify the system that defines feedbacks in terms of global–time-mean changes in surface temperature nor is there any compelling empirical evidence to do so. The lack of maturity of feedback analysis methods also suggests that progress in understanding climate feedback will require development of alternative methods of analysis. It has been argued that, in view of the complex nature of the climate system, and the cumbersome problems encountered in diagnosing feedbacks, understanding cloud feedback will be gleaned neither from observations nor proved from simple theoretical argument alone. The blueprint for progress must follow a more arduous path that requires a carefully orchestrated and systematic combination of model and observations. Models provide the tool for diagnosing processes and quantifying feedbacks while observations provide the essential test of the model’s credibility in representing these processes. While GCM climate and NWP models represent the most complete description of all the interactions between the processes that presumably establish the main cloud feedbacks, the weak link in the use of these models lies in the cloud parameterization imbedded in them. Aspects of these parameterizations remain worrisome, containing levels of empiricism and assumptions that are hard to evaluate with current global observations. Clearly observationally based methods for evaluating cloud parameterizations are an important element in the road map to progress. Although progress in understanding the cloud feedback problem has been slow and confused by past analysis, there are legitimate reasons outlined in the paper that give hope for real progress in the future.

The present paper shows how the well-known similarity and scaling concepts are properties of the radiative transfer equation and not specifically of the degree of anisotropy of the phase function. It is shown that the key assumption regarding the angular dependence of the radiative field is essential in determining both the value for the parameter used to scale the radiative transfer, as well as the number of streams used in calculating the radiances for various atmospheric problems. Simulations performed on realistic type of cirrus clouds, characterized by strongly anisotropic functions, demonstrates the superior computational advantage for accurately simulating radiances. A new approach for determining the scaling parameter is introduced.

Different approaches for parameterizing the effects of vertical variability of cloudiness on radiative transfer are assessed using a database constructed from observations derived from lidar and millimeter cloud radar data collected from three different locations. Five different methods for dealing with the vertical overlap of clouds were incorporated into a single radiation model that was applied to the lidar/radar data averaged in time. The calculated fluxes and heating rates derived with this model are compared to broadband fluxes and heating rates calculated with the independent column approximation using the time-resolved cloud data. These comparisons provide a way of evaluating the effects of different overlap assumptions on the calculation of domain-mean fluxes. It was demonstrated how two of the most commonly used overlap schemes, the random and maximum-random methods, suffer a severe problem in that the total cloud amount defined by these methods depends on the vertical resolution of the...

The primary purpose of this study is to assess the performance of 1D solar radiative transfer codes that are used currently both for research and in weather and climate models. Emphasis is on interpretation and handling of unresolved clouds. Answers are sought to the following questions: (i) How well do 1D solar codes interpret and handle columns of information pertaining to partly cloudy atmospheres? (ii) Regardless of the adequacy of their assumptions about unresolved clouds, do 1D solar codes perform as intended? One clear-sky and two plane-parallel, homogeneous (PPH) overcast cloud cases serve to elucidate 1D model differences due to varying treatments of gaseous transmittances, cloud optical properties, and basic radiative transfer. The remaining four cases involve 3D distributions of cloud water and water vapor as simulated by cloud-resolving models. Results for 25 1D codes, which included two line-by-line (LBL) models (clear and overcast only) and four 3D Monte Carlo (MC) photon transport ...

The inference of optical depth and particle size of clouds and aerosols using remotely sensed reflected radiance at solar wavelengths has received much attention recently. The information these measurements provide is path integrated. However, very little is known about the vertical distribution of this weighting. To characterize it, we first solve the radiative transfer equation (RTE) by a Green's function approach, and then investigate the sensitivity of the weighting to vertical inhomogeneities in the extinction by introducing a function that is closely related to the Green's function, herein called the contribution function. This function calculates the contributions to the radiance at the upper boundary of the medium by underlying layers. Three hypothetical clouds of identical optical depth but exhibiting different extinction profiles were used in this study. The contribution function was found very sensitive to the extinction profile. The global reflection and transmission matrices used to construct the Green's function, derived using an eigenmatrix method, resulted in an efficient, stable, and accurate method for calculating the emerging radiances that can be extended to multi-layered media.

This paper describes simple, computationally efficient methods of calculating 2-stream broadband fluxes and heating rates in the shortwave and longwave for multilayered media. The method, herein referred to as selection rules, is used in conjunction with conventional 2-stream solvers to reduce the number of full-up radiative transfer calculations, thus decreasing the computation time.

This paper outlines a radiation parameterization method for deriving broadband fluxes that is currently being implemented in a number of global and regional atmospheric models. The rationale for the use of the 2-stream method as a way of solving the radiative transfer problem for broadband solar and longwave fluxes is presented. This rationale is based on assessment of these models in the context of a novel method of classifying radiative transfer problems that more clearly identifies the types of problems encountered in calculating globally distributed broadband fluxes. The delta-Eddington model (DEM) and the constant-hemispheric 2-stream models (CHMs) are shown to be superior to other 2-stream methods of solution under this classification and also superior to 4-stream solutions for the many classes of problems relevant to modeling the global atmosphere. These two methods are used to construct a radiation model of broadband solar and IR fluxes based on the k-distribution data of Fu and Liou. Whe...

This paper investigates the expected capabilities of the new generation of infrared satellite sounders for detecting CO2. A general circulation model is used to simulate realistic CO2 fields and to define the needed accuracy of CO2 observations in order to be useful in constraining surface sources and sinks of CO2, which will be described in more detail in a future paper. Optimal estimation retrieval theory is then used to determine the possible accuracy of the satellite measurements and to define the retrieval characteristics. A discussion of several factors that affect the retrievals is also included. We conclude that tropospheric column retrievals of CO2 are possible with an accuracy of better than 1 ppmv on a monthly mean basis. Several factors, like thin cirrus clouds and radiative transfer modeling errors, will degrade these results if not carefully accounted for. The possibility of extensive time and spatial averaging of the satellite observations will overcome some of these problems.

In the years preceding the launch of CloudSat in 2003, important questions regarding instrument requirements sufficient to fulfilling the mission's science objectives must be addressed. Qualified and useful answers to these questions require in turn a careful simulation strategy whereupon the observing system and modeled environment are represented as realistically as possible. In this paper, we consider the W band (94 GHz) cloud radar minimum detectable signal (MDS) requirement in the context of specified boundary fluxes and in-cloud heating rates. Realistic cloud distribution and water contents from short-range forecasts produced by the European Centre for Medium-Range Weather Forecasts (ECMWF) are converted to attenuated equivalent radar reflectivity to yield full-orbit virtual CloudSat observations. The radiative implications of variable radar MDS are examined using a two-stream radiative transfer model. Simulations show that a MDS of ∼−28 dBZ will detect a fraction of the true cloud field sufficient to reconstruct the instantaneous top-of-atmosphere and surface fluxes to within Clouds and the Earth's Radiant Energy System (CERES) requirements. The results of this analysis form collectively a statement on instrument engineering requirements that is predicated on and hence mappable directly to the physical parameters that define CloudSat science objectives.

This note is an introduction to the reprint of the 1991 JQSRT article “A new polarized atmospheric radiative transfer model” by K.F. Evans and G.L. Stephens. We discuss the significance of the article, how our two plane-parallel polarized radiative transfer codes came about, how our codes have been used, and more recent developments in polarized radiative transfer modeling.

The U.S. Department of Energy has established an unmanned aerospace vehicle (UAV) measurement program. The purpose of this paper is to describe the evolution of the program since its inception, review the progress of the program, summarize the measurement capabilities developed under the program, illustrate key results from the various UAV campaigns carried out to date, and provide a sense of the future direction of the program. The Atmospheric Radiation Measurement (ARM)–UAV program has demonstrated how measurements from unmanned aircraft platforms operating under the various constraints imposed by different science experiments can contribute to our understanding of cloud and radiative processes. The program was first introduced in 1991 and has evolved in the form of four phases of activity each culminating in one or more flight campaigns. A total of 8 flight campaigns produced over 140 h of science flights using three different UAV platforms. The UAV platforms and their capabilities are describ...

This paper describes computationally efficient methods of solving the two-stream plane-parallel equation of radiative transfer in multi-layered media using adjoint perturbations in combination with selection rules. Semi-analytical results are obtained for the perturbed fluxes in atmospheres illuminated by solar radiation. The perturbation approach is useful in media dominated by multiple scattering whereas selection rules apply when absorption is dominant or if the media is weakly scattering. Selection rules can be applied with conventional two-stream solvers to reduce the number of radiative transfer calculations. For example, clear sky broadband fluxes computed with selection rules for a 30 layer atmosphere using the k -distribution method were obtained in about one-seventh the time taken by the standard solvers. An 12-fold increase in computational speed over the standard solvers was achieved when selection rules were used with the perturbation method for the same atmosphere. Fluxes so computed were within 10% of those calculated using standard, full up two-stream radiative transfer codes.

This paper explores the feasibility of using O 2 A-band reflectance spectra in the retrieval of cloud optical and physical properties. Analyses demonstrate that these reflection spectra are sensitive to optical properties of clouds such as optical depth t c and phase function, vertical profile information including cloud-top pressure, pressure thickness, and the surface albedo. An estimation method is developed to demonstrate how well this information might be retrieved from synthetic spectra calculated by a line-by-line spectral multiple scattering model assuming realistic instrument parameters (spectral resolution, calibration accuracy, and signal-to-noise properties). The quality of the retrievals is expressed in terms of two indices, one relating to total error and another that quantifies the extent of reliance of the retrieval on the measurement, or conversely on other a priori information. Sources of total error include instrument-related errors, forward model errors including phase function errors, and errors in a priori data. The retrievals presented show the following: (i) The optical depth, surface albedo, cloud-top pressure, and cloud layer pressure thickness can be retrieved with an accuracy of approximately 5% for most cases of low cloud except when these clouds are optically thin and over bright surfaces. The spectra also contain information about the pressure thickness of the low-level cloud and this information also can be retrieved with an expected accuracy of less than 10% and with little reliance on any a priori data. (ii) Significantly larger errors result for retrievals for high clouds when no attempt is made to constrain the uncertainties associated with the unknown character of the scattering phase function. (iii) Retrieval of a limited amount of information about the phase function is possible under certain circumstances. It is possible to retrieve the asymmetry parameter sufficiently well to improve the accuracy of the forward model. This results in a shrinking of the errors in t c to less than 10% for t c . 0.1. (iv) The pressure information about scattering layers inherent in the A-band spectra is shown to provide a limited amount of vertical profiling capability (four to five layers of information at the most) provided the measurements are obtained with a spectral resolution of about 0.5 cm21 and obtained with an accuracy of 2% or better. A specific example demonstrates the capability of not only detecting the presence of thin high cloud above lower brighter cloud but also the capability of estimating the optical depths of both clouds. (v) The advantage of additional information such as provided by active profilers (radar and lidar) is explored. The advantages of this additional profile information are quantitatively shown to improve not only the retrieval of vertical profiles of extinction but also the optical properties of individual cloud layers.

This paper introduces several new variations of the equivalence theorem of Irvine [1964] which may increase the speed and accuracy of spectral radiative transfer models that calculate spectral radiance or flux. Using this theory, spectral gaseous, cloud, and surface absorptions are accommodated by integrating or summing over photon path length and scattering probability density functions (pdfs) after the completion of the multiple-scattering calculation. This procedure can be performed for absorption coefficients at any spectral resolution within a wavelength interval in which scattering properties of the atmosphere can be considered constant. This technique eliminates the need to run the multiple-scattering portion of a model more than once for each interval in lieu of integration and/or summation. If this procedure can be performed efficiently, dramatic increases in model speed may be realized. Also, because absorption coefficient spectral resolution can be extremely fine, the need for approximations or parameterizations is eliminated, increasing model accuracy. Unlike the original derivation, the new version of the gaseous absorption equation allows the use of complex model scattering atmospheres. An approximation is introduced which allows the use of gas profiles which vary in the vertical. Because employment of the complete theory requires a relatively large amount of computer memory, a pdf approximation is introduced to make it tractable. Validation of each relation is presented using a Monte Carlo model simulating shortwave flux. An example of shortwave flux transmitted through a three-dimensional model atmosphere obtained from the Monte Carlo/equivalence theorem (MC/ET) model is shown along with an analysis of the effect of constant scattering property wavelength interval size on the resulting broadband flux.

SUMMARY We have developed a simple, analytically tractable radiativexonvective model of the tropical climate system that includes an explicit moisture budget, a simple convection parametrization, a simple but physically based radiation parametrization, and interactive clouds. The underlying surface is assumed to be ocean. The model includes prognostic equations for the sea surface temperature and the vertically integrated water vapour content. A stratosphere in radiative equilibrium limits the depth of the convective layer. The lower-tropospheric lapse rate, surface evaporation rate, and clear-sky long-wave and short-wave radiative fluxes at the surface and the top of the atmosphere are determined as functions of the sea surface temperature and precipitable water only. The radiativeconvective equilibria of the model atmosphere resemble the observed tropical climate, if realistic sea surface temperatures are prescribed. However, cloud-free radiativexonvective equilibria of the tropical atmosphere-ocean system do not occur for realistic values of the surface albedo. When cloud radiative effects are included, the model produces radiativexonvective equilibria that are unrealistically warm. With prescribed realistic lateral energy and moisture transports, however, the equilibria of the model are realistic.

The importance of aerosols as agents of climate change has recently been highlighted. However, the magnitude of aerosol forcing by scattering of shortwave radiation (direct forcing) is still very uncertain even for the relatively well characterized sulfate aerosol. A potential source of uncertainty is in the model representation of aerosol optical properties and aerosol influences on radiative transfer in the atmosphere. Although radiative transfer methods and codes have been compared in the past, these comparisons have not focused on aerosol forcing (change in net radiative flux at the top of the atmosphere). Here we report results of a project involving 12 groups using 15 models to examine radiative forcing by sulfate aerosol for a wide range of values of particle radius, aerosol optical depth, surface albedo, and solar zenith angle. Among the models that were employed were high and low spectral resolution models incorporating a variety of radiative transfer approximations as well as a line-by-line model. The normalized forcings (forcing per sulfate column burden) obtained with the several radiative transfer models were examined, and the discrepancies were characterized. All models simulate forcings of comparable amplitude and exhibit a similar dependence on input parameters. As expected for a non-light-absorbing aerosol, forcings were negative (cooling influence) except at high surface albedo combined with small solar zenith angle. The relative standard deviation of the zenith-angle-averaged normalized broadband forcing for 15 models-was 8% for particle radius near the maximum in this forcing (approx. 0.2 microns) and at low surface albedo. Somewhat greater model-to-model discrepancies were exhibited at specific solar zenith angles. Still greater discrepancies were exhibited at small particle radii and much greater discrepancies were exhibited at high surface albedos, at which the forcing changes sign; in these situations, however, the normalized forcing is quite small quite small. Discrepancies among the models arise from inaccuracies in Mie calculations, differing treatment of the angular scattering phase function, differing wavelength and angular resolution, and differing treatment of multiple scattering. These results imply the need for standardized radiative transfer methods tailored to the direct aerosol forcing problem. However, the relatively small spread in these results suggests that the uncertainty in forcing arising from the treatment of radiative forcing of a well-characterized aerosol at well-specified surface albedo is smaller than some of the other sources of uncertainty in estimates of direct forcing by anthropogenic sulfate aerosols and anthropogenic aerosols generally.

This paper describes a computationally efficient method for solving the plane parallel equation of radiative transfer for the two-stream fluxes based on the adjoint perturbation formulation. Analytical results for the perturbed fluxes are presented for a single layer atmosphere containing both solar and thermal sources. Simple linear and exponential corrections to the base state fluxes are explored. For the solar radiative transfer problem, the exponential form of the perturbation correction can accommodate deviations exceeding 400% in the base state optical properties while maintaining accuracy to within a few percent. For thermal radiative transfer, the linear form of perturbation relation is the more accurate, but unlike the solar problem, deviations from the base state optical properties must remain relatively small (less than 20%) if the errors in the computed fluxes are to remain within a few percent of the true fluxes. The method is applied to the calculation of broadband solar fluxes in a layer of scatterers embedded in an absorbing gas, where the absorption is modeled via the k-distribution method.

This paper introduces a radiative transfer model for the 9.6-μm ozone band that specifically matches the TIROS operational vertical sounder (TOVS) channel 9. The model is based on a spectral Malkmus band model for transmission. Band parameters were calculated by comparing to MODTRAN3 derived radiances. The effect of pressure on absorption is dealt with using a four-parameter approximation, and the improvements of this approximation over the more common Van de Hulst-Curtis-Godson scaling approximation are assessed. While this new model is exploited in the development of the retrieval described in this paper, the result has wider applicability to ozone climate problems requiring calculation of the radiative forcing associated with changing ozone. A two-layer version of the radiative transfer model is implemented in a retrieval scheme to obtain total ozone amounts from radiances measured by the TOVS instrument. Because the TOVS ozone channel is mainly sensitive to lower stratospheric ozone, ozone columns of the upper layer (above 30 hPa and with mean pressure of 10 hPa) are prescribed as a function of latitude. Ozone columns of the lower layer (mean pressure of 105 hPa) are then retrieved. The retrieval is based on a nonlinear optimal estimation algorithm and provides definition of error characteristics for every retrieval, which makes it possible to obtain a spatial distribution of the errors in the retrieval together with the spatial distribution of the retrieved total ozone column itself. This global distribution of the retrieval error and also of the contribution of a priori knowledge to the retrieval is presented to provide a validity of the ozone retrievals. Total ozone mapping spectrometer (TOMS) statistics are used as a priori information in the retrieval, and the 40-layer model is used to estimate the forward model error of the two-layer model. Comparisons of ozone retrievals for 1989 with TOMS total ozone measurements show good agreement both in time and in space with a rms difference between 1% and 3% for zonal means and 10% for global gridded measurements.

Recent estimates of the effect of increasing amounts of anthropogenic sulfate aerosol on the radiative forcing of the atmosphere have indicated that its impact may be comparable in magnitude to the effect from increases in CO2. Much of this impact is expected from the effects of the aerosol on cloud microphysics and the subsequent impact on cloud albedo. However, internal horizontal variations in cloud optical properties are also known to affect cloud albedo. A solar broadband version of a 2D radiative transfer model was used to quantify the impact of enhanced aerosol concentrations and horizontal inhomogeneity on the solar broadband albedo of marine stratus. The 2D cross sections of cloud physics data taken from a set of 3D RAMS/LES simulations of marine stratus provided realistic optical property data for radiative transfer simulations. A control run using typical marine CCN concentrations and a sensitivity study using enhanced concentrations of CCN were examined. The results of the radiative t...

One of the major sources of uncertainty in climate studies is the detection of cirrus clouds and characterization of their radiative properties. Combinations of water vapor absorption channels (e.g., 1.38 µm), ice-water absorption channels (e.g., 1.64 µm), and atmospheric window channels (e.g., 11 µm) in the imager, together with a lidar profiler on future EOS platforms, will contribute to enhancing our understanding of cirrus clouds. The aforementioned spectral channels are used in this study to explore the effects exerted by uncertainties in cloud microphysical properties (e.g., particle size distribution) and cloud morphology on the apparent radiative properties, such as spectral reflectance and heating and cooling rate profiles. As in Part I of our previous study, which establishes the foundations of the Fourier-Riccati method of radiative transfer in inhomogeneous media, cloud extinction and scattering functions are characterized by simple spatial variations with measured and hypothesized mi...

This paper presents the results of a detailed study of the microwave single scattering properties of ice crystals expected in cirrus clouds. The discrete dipole approximation is used to compute scattering quantities of particles ranging in size from 30 to 2000 µm at 85.5, 157, 220, and 340 0Hz. Five shapes were simulated: solid and hollow columns, hexagonal plates, planar bullet rosettes, and equivalent-volume spheres. The scattering properties were computed for 18 Gamma size distributions with a range of characteristic particle size and distribution width. The results indicate that particle shape has a significant effect; for example, there is a range of about 3 in extinction over the five shapes for the same size distribution and ice water content. Crystal shape is the dominant effect on le polarization of the scattering, with the thinner shapes having the more polarizing effect. The characteristic particle size has the greatest impact on the extinction and single-scattering albedo, while the d...

This paper presents the results of polarized microwave radiative transfer modeling of cirrus clouds containing five different particle shoes and 18 Gamma size distributions. Upwelling brightness temperatures for tropical and midlatitude winter atmospheres are simulated at 85.5, 157, 220, and 340 GHz using scattering properties computed with the discrete dipole approximation (described in Part I). The key parameter for the results is the sensitivity (ΔTb/IWP), which relates the modeled brightness temperature depression to the ice water path. It is shown that for the higher frequencies or distributions of larger particles (i.e., in the scattering regime) the sensitivity is nearly independent of cloud temperature and details of the underlying atmosphere. As expected from the single-scattering results, the characteristic particle size has a large effect on the sensitivity, while the distribution width has only a minor effect. The range in sensitivity over the five particle shapes is typically a facto...

The authors present an observationally based evaluation of the vertically resolved cloud ice water content (CIWC) and vertically integrated cloud ice water path (CIWP) as well as radiative shortwave flux downward at the surface (RSDS), reflected shortwave (RSUT), and radiative longwave flux upward at top of atmosphere (RLUT) of present-day global climate models (GCMs), notably twentieth-century simulations from the fifth phase of the Coupled Model Intercomparison Project (CMIP5), and compare these results to those of the third phase of the Coupled Model Intercomparison Project (CMIP3) and two recent reanalyses. Three different CloudSat and/or Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) combined ice water products and two methods are used to remove the contribution from the convective core ice mass and/or precipitating cloud hydrometeors with variable sizes and falling speeds so that a robust observational estimate can be obtained for model evaluations. The results show that, for annual mean CIWC and CIWP, there are factors of 2–10 (either over- or underestimate) in the differences between observations and models for a majority of the GCMs and for a number of regions. Most of the GCMs in CMIP3 and CMIP5 significantly underestimate the total ice water mass because models only consider suspended cloud mass, ignoring falling and convective core cloud mass. For the annual means of RSDS, RLUT, and RSUT, a majority of the models have significant regional biases ranging from −30 to 30 W m−2. Based on these biases in the annual means, there is virtually no progress in the simulation fidelity of RSDS, RLUT, and RSUT fluxes from CMIP3 to CMIP5, even though there is about a 50% bias reduction improvement of global annual mean CIWP from CMIP3 to CMIP5. It is concluded that at least a part of these persistent biases stem from the common GCM practice of ignoring the effects of precipitating and/or convective core ice and liquid in their radiation calculations.

A multichannel passive microwave precipitation retrieval algorithm is developed. Bayes theorem is used to combine statistical information from numerical cloud models with forward radiative transfer modeling. Amultivariate lognormal prior probability distribution contains the covariance information about hydrometeor distributions that resolves the nonuniqueness inherent in the inversion process. Hydrometeor profiles are retrieved by maximizing the posterior probability density for each vector of observations. The hydrometeor profile retrievalmethod is tested with data from the Advanced Microwave Precipitation Radiometer (IO, 19, 37, and 85 GHz) of convection over ocean and land in Florida. The CP-2 multiparameter radar data are used to verify theretrieved profiles. The results show that the method can retrieve approximate hydrometeor profiles, with larger errors over land than water. There is considerably greater accuracy in the retrieval of integrated hydrometeor contents than of profiles. Many of the retrieval errors are traced to problems with the cloud model microphysicalinformation, and future improvements to the algorithm are suggested.

This paper presents a comparison of column water vapor (CWV) information derived from both infrared measurements as part of the TIROS-N Operational Vertical Sounder (TOVS) and Special Sensor Microwave/Imager (SSM/I) in an attempt to assess the relative merits of each kind of data. From the analyses presented in this paper, it appears that both types of satellite data closely reproduce the bulk climatological relationships introduced in earlier studies using different data. This includes both the bulk relationship between CWV and the sea surface temperature and the annual variation of CWV over the world's oceans. The TOVS water vapor data tends to be systematically smaller than the SSM/I data and when averaged over the ocean covered regions of the globe this difference is between 2–3 kgm−2. Using a cloud liquid water threshold technique to establish clear sky values of SSM/I water vapor, we conclude that the differences between TOVS and SSM/I are largely a result of the clear sky bias in TOVS sampling except in the subsidence regions of the subtropics. The clear sky bias is considerably smaller than previously reported and we attribute this improvement to the new physical retrieval scheme implemented by NOAA NESDIS. While there is considerable agreement between the two types of satellite data, there are also important differences. In regions where there is drying associated with large scale subsidence of the atmosphere, the TOVS CWV's are too moist relative to both radiosonde and SSM/I data and this difference may exceed 10 kgm−2. The explanation for this difference lies in the limitations of infrared radiative transfer. By contrast, in regions of deep convection, such as in the ITCZ, TOVS CWV is systematically lower than the SSM/I CWV. Both TOVS and SSM/I data demonstrate similar kinds of gross effects of large scale circulation on the water vapor except in these subsidence regions where TOVS data leads to an under-prediction of the effects of subsidence drying.

The three-dimensional equation of radiative transfer is formally solved using a Fourier-Riccati approach while calculations are performed on cloudy media embedded in a two-dimensional space. An extension to Stephens' work this study addresses the coupling between space and angle asserted by the equation of transfer. In particular, the accuracy of the computed radiation field as it is influenced by the angular resolution of the phase function and spatial discretization of the cloudy medium is discussed. The necessity of using a large number of quadrature points to calculate fluxes even when the phase function is isotropic for media exhibiting vertical and horizontal inhomogeneities is demonstrated. Effects of incorrect spatial sampling on both radiance and flux fields are also quantified by example. Radiance and flux comparisons obtained by the Fourier-Riccati model and the independent pixel approximation for inhomogeneous cloudy media illustrate the inadequacy of the latter even for tenuous clouds.

A method to determine cirrus cloud effective radii remotely using lidar and radar backscatter data is presented. The difference in backscattered returns from instruments widely separated in wavelength holds information on the characteristic sizes of the scatterers. The method compares theoretically expected backscatter coefficients to observed backscatter returns from NOAA's 3.2-cm and 8.6-mm radars and the 10.6-µm lidar. Measurements were taken during a two-phase cloud experiment held in northeastern Colorado from 6 September to 5 October 1989 and 15 February to 31 March 1991. It was found that the particle sizes estimated from the lidar-radar method agree closely with in situ aircraft measurements. Case studies are presented to demonstrate the method and the potential for multiwavelength remote sensing of cirrus cloud radiative properties.

This paper describes calculations of the spatial and temporal variation of the radiation budget of a tropical mesoscale convective system (MCS). A combination of cloud model simulations, radiation model simulations, and analyses of observations obtained during the Equatorial Mesoscale Experiment (EMEX), the Stratosphere-Troposphere Exchange Program (STEP), and the Australian Monsoon Experiment (AMEX) are used to obtain these heating rates. The two-dimensional version of the Colorado State University regional atmospheric modeling system is used to simulate a tropical MCS that occurred during EMEX mission 9 on February 2, 1987. The simulation is shown to broadly agree with the observations reported in a related paper. The spatial radiative heating distributions derived from a two-stream radiative transfer model corresponding to the mature stage of the simulated cloud system indicate that significant horizontal inhomogeneities exist. According to the model results the effects of the MCS are to (1) increase in the infrared emission to the surface and to decrease in the net infrared energy loss from the atmosphere relative to the clear sky emission and (2) change the transmission of solar flux to the surface, the shortwave albedo of the atmosphere, and the solar absorption in the atmosphere. The results show how the MCS significantly reduces the solar flux to the surface relative to the clear sky values and that the largest reduction occurs under the convective portions of the mature MCS. (3) The MCS creates a total (solar plus infrared) radiative warming in the atmosphere relative to the surrounding clear sky. The value of this total heating is governed by both infrared and solar absorption. Vertical profiles of this heating show the dominance of infrared cooling near cloud top and infrared heating inside and near cloud base. The shortwave heating rate can also be as large as the infrared cooling near the cloud top region of the tropical MCS, especially at a local noon. (4) The temporal changes in radiation profiles also demonstrate how the MCS modulates the radiation budget of the atmosphere. Specifically, the total radiation energy loss of the entire two-dimensional domain of the model atmosphere decreases and eventually becomes positive as the cloud system decays, becomes a stratiform in nature, and fills the domain. This change in the column divergence of flux translates into a total column radiative heating rate of approximately 1.7 K/d (relative to the clear sky radiative cooling rate). The solar component of this domain heating tends to be concentrated in the upper troposphere, whereas the infrared component of the heating is spread over the lower and middle troposphere. These results also show how tropical mesoscale cloud system provides an effective radiative heat source for the tropical atmosphere.

An approximate method for estimating the global distributions of the entropy fluxes flowing through the upper boundary of the climate system is introduced, and an estimate of the entropy exchange between the earth and space and the entropy production of the planet is provided. Entropy fluxes calculated from the Earth Radiation Budget Experiment measurements show how the long-wave entropy flux densities dominate the total entropy fluxes at all latitudes compared with the entropy flux densities associated with reflected sunlight, although the short-wave flux densities are important in the context of clear sky-cloudy sky net entropy flux differences. It is suggested that the entropy production of the planet is both constant for the 36 months of data considered and very near its maximum possible value. The mean value of this production is 0.68 x 10 exp 15 W/K, and the amplitude of the annual cycle is approximately 1 to 2 percent of this value.

In recent years, it has been revealed that the cloud microphysical properties such as cloud particle radii obtained from satellite remote sensing were of apparent values. A combined use of passive and active sensor has gradually revealed about what we observed using passive imager thorough the vertical information of clouds obtained from active sensors. For understanding the process of cloud growth in nature, model that simulates cloud droplet growth is also needed. Observation results obtained from the satellite remote sensing are used for validating model such as cloud resolving model and spectral-bin microphysics cloud model. Vice-versa, models are used for understanding the process that are hidden in satellite-remote sensing results. We are aiming consistent understanding of clouds with observation and modeling. In this paper, we will introduce a preliminary result of multi-sensor view of warm water clouds and we will review our research strategy of cloud sciences, using satellite remote sensing, the cloud growth model, and the radiative transfer.