Single-column Atmospheric Model Research Articles

LB-SCAM: a learning-based method for efficient large-scale sensitivity analysis and tuning of the Single Column Atmosphere Model (SCAM)

Abstract. The single-column model, with its advantages of low computational cost and fast execution speed, can assist users in gaining a more intuitive understanding of the impact of parameters on the simulated results of climate models. It plays a crucial role in the study of parameterization schemes, allowing for a more direct exploration of the influence of parameters on climate model simulations. In this paper, we employed various methods to conduct sensitivity analyses on the 11 parameters of the Single Column Atmospheric Model (SCAM). We explored their impact on output variables such as precipitation, temperature, humidity, and cloud cover, among others, across five test cases. To further expedite experimentation, we utilized machine learning methods to train surrogate models for the aforementioned cases. Additionally, three-parameter joint perturbation experiments were conducted based on these surrogate models to validate the combined parameter effects on the results. Subsequently, targeting the sensitive parameter combinations identified from the aforementioned experiments, we further conducted parameter tuning for the corresponding test cases to minimize the discrepancy between the results of SCAM and observational data. Our proposed method not only enhances model performance but also expedites parameter tuning speed, demonstrating good generality at the same time.

Assessment of nonlinear effects of a deep subgrid lake with an atmospheric single‐column model

AbstractSome nonlinear aspects due to the coupling of a single column atmospheric model (SCM) with both a land‐surface model (LSM) and a lake model has lately been published by Goyette in 2017. In this previous study, the surface type abruptly changed from land to an open water surface. This article further investigates the potential of this SCM to explore the nonlinear effects through the analysis of the impacts of fractional land and open water surfaces on the surface fluxes and variables, as well as on the atmospheric air temperature, specific humidity, and wind speed vertical profiles, with an application to deep Lake Geneva, Switzerland. It is shown that the coupling methodology depending on the surface type produced realistic and coherent results and indicated that the mean fluxes and other relevant quantities may not be simply averaged on the basis of the fractional area of the land and that of the open water. If Lake Geneva relative surface area is prescribed to its observed value with respect to the model grid‐mesh size, the remaining being land surface, results showed maximum seasonal mean differences of 7.5 and 5.4 W·m−2 for the latent and sensible heat flux in Autumn respectively, 1.6°C, 0.8 g·kg−1 for the screen‐level air temperature and specific humidity in Autumn respectively, and 0.6 m·s−1 for the anemometer‐level windspeed in Winter with respect to the original land surface, owing to the different behaviour of the vertical turbulent transfer of heat, moisture and momentum but also to the different thermal and radiative characteristics of land and water surfaces.

Atmospheric Boundary Layer Turbulence Closure Scheme for Wind-Following Swell Conditions

Abstract Over the ocean, atmospheric boundary layer turbulence can be altered by underlying waves. Under swell conditions, the impact of waves on the atmosphere is more complicated compared to that under wind-wave conditions. Based on large-eddy simulation (LES), the wind-following swell impact on the atmospheric boundary layer is investigated through three terms: swell-induced surface momentum flux, the vertical profile of swell-induced momentum flux, and the swell impact on atmospheric mixing. The swell-induced surface momentum flux displays a decreasing trend with increasing atmospheric convection. The swell-induced momentum flux decays approximately exponentially with height. Compared with atmospheric convection, the decay coefficient is more sensitive to wave age. Atmospheric mixing is enhanced under swell conditions relative to a flat stationary surface. The swell impact on the atmospheric boundary layer is incorporated into a turbulence closure parameterization through the three terms. The modified turbulence closure parameterization is introduced into a single-column atmospheric model to simulate LES cases. Adding only the swell impact on the atmospheric mixing has a limited influence on wind profiles. Adding both the impact of swell on the atmospheric mixing and the profile of swell-induced momentum flux significantly improves the agreement between the 1D atmospheric simulation results and the LES results, to some extent simulating the wave-induced low-level wind jet. It is concluded that the swell impact should be included in atmospheric numerical models.

Biospheric and anthropogenic contributors to atmospheric CO2 variability in a residential neighborhood of Phoenix, Arizona

AbstractUrban environment contributes significantly to the global carbon cycle with complex governing mechanisms due to the combined biospheric and anthropogenic contributors. In this study, we analyzed the patterns of boundary layer CO2 flux and concentration for a residential neighborhood in Phoenix, Arizona by using the eddy covariance technique and a single column atmospheric model. Atmospheric stability, anthropogenic emission, and biogenic effect are found to be key determinants to atmospheric CO2 variability. In a diurnal cycle, two CO2 flux peaks coincide with morning and afternoon peak traffic hours, exemplifying the influence of traffic emissions. In the annual cycle, maximum CO2 concentration is found in winter, mainly due to additional emission from the combustion of natural gas combined with the effect of poor dispersion. On the other hand, the minimum CO2 concentration is found in the spring and is attributable to the strong convective mixing and active vegetation uptake. In addition, prominent hysteresis has been found between the atmospheric CO2 concentration and air temperature with a “plait‐shaped” pattern in the diurnal cycle and an “oval‐shaped” loop for the seasonal variability.

Impacts of mesic and xeric urban vegetation on outdoor thermal comfort and microclimate in Phoenix, AZ

Urban vegetation is an effective way in mitigating excessive heat and improving the outdoor thermal environment for residents in cities via evaporative cooling. Different urban vegetation forms (mesic or xeric) alter surface energy and water budgets in different ways, which is further complicated by interactions with buildings and anthropogenic controls. Mesic vegetation such as lawns reduces urban temperatures by evaporative cooling but requires large amounts of water for continuous irrigation. On the other hand, xeric vegetation such as shade trees reduces urban temperatures mainly through shading and has low water demand. The objective of this study is to investigate the impacts of different vegetation forms on microclimate in a hot desert city – Phoenix, AZ. We applied an advanced urban canopy model coupled with a single-column atmospheric model to simulate urban boundary layer dynamics over different landscaping scenarios with different combinations of mesic and xeric vegetation forms. We subsequently compared the urban land surface temperatures, near-surface air temperatures, outdoor thermal comfort in the urban canopy layer, as well as atmospheric dynamics (temperature, humidity) in the overlying boundary layer for a set of different scenarios.

Low clouds suppress Arctic air formation and amplify high-latitude continental winter warming

High-latitude continents have warmed much more rapidly in recent decades than the rest of the globe, especially in winter, and the maintenance of warm, frost-free conditions in continental interiors in winter has been a long-standing problem of past equable climates. We use an idealized single-column atmospheric model across a range of conditions to study the polar night process of air mass transformation from high-latitude maritime air, with a prescribed initial temperature profile, to much colder high-latitude continental air. We find that a low-cloud feedback--consisting of a robust increase in the duration of optically thick liquid clouds with warming of the initial state--slows radiative cooling of the surface and amplifies continental warming. This low-cloud feedback increases the continental surface air temperature by roughly two degrees for each degree increase of the initial maritime surface air temperature, effectively suppressing Arctic air formation. The time it takes for the surface air temperature to drop below freezing increases nonlinearly to ∼ 10 d for initial maritime surface air temperatures of 20 °C. These results, supplemented by an analysis of Coupled Model Intercomparison Project phase 5 climate model runs that shows large increases in cloud water path and surface cloud longwave forcing in warmer climates, suggest that the "lapse rate feedback" in simulations of anthropogenic climate change may be related to the influence of low clouds on the stratification of the lower troposphere. The results also indicate that optically thick stratus cloud decks could help to maintain frost-free winter continental interiors in equable climates.

Interfacing a one‐dimensional lake model with a single‐column atmospheric model: Application to the deep Lake Geneva, Switzerland

A single column atmospheric model (SCM) coupled to a one‐dimensional lake model devised for climate simulations is described in this paper. As a test case, this coupled model is applied to the deepest section of Lake Geneva in Switzerland. Both atmospheric and lake models require a minimal set of adjustable parameters to reproduce the local observations of temperature, moisture, and wind as well as those of the lake thermal profiles. A number of simulations have been performed to produce a sorted set of optimal model parameters that reproduces the mean and the variability of the seasonal evolution of the thermal profiles in the lake as well as those of the mean and the variability of the surface air temperature, moisture, and winds. The lake water temperature is reproduced realistically using the optimal calibration parameter values with a seasonal‐ and depth‐averaged error of 0.41°C in summer, −0.15°C in autumn, 0.01°C in winter, and 0.27°C in spring when compared to the lake observations. Also, the errors of the seasonally averaged simulated anemometer‐level wind speed, screen‐level air temperature, and specific humidity to the station‐derived values are 0.04 m s−1, 1.04°C, and 0.74 g kg−1, respectively. Results of this study contribute to the understanding of the air‐lake interactions present over the deep Lake Geneva. In addition, the sensitivity experiments carried out in this paper serve as the basis for experiments aiming at studying the thermal response of the deep Swiss Lake Geneva under future global climate change conditions reported in a companion paper.

Modelling and analysis of the impact of irrigation on local arid climate over northwest China

AbstractThis study focuses on how irrigation processes affect local climate over arid areas. The chosen study area is northwest China, a typical arid region where three dominant land‐use types are irrigated cropland, grassland, and desert. Observational analysis indicates that the highest precipitation, the coolest surface temperatures, and the slowest warming trend are seen over irrigated cropland from 1979 to 2005. The single column atmospheric model (SCAM), developed by the National Center for Atmospheric Research (NCAR), was used to investigate and better understand the differences in long‐term climate conditions and change over the above three land‐use types. The results indicate that local climate conditions are predominantly controlled by large‐scale forcing in this arid region and that local land surface forcing related to vegetation cover change and irrigation processes also has a significant impact. This study strongly suggests that a realistic climate forecast for this region can be achieved only with both accurate large‐scale and local climate forcing. The irrigated cropland of the region generates stronger evaporation that cools the surface and slows the warming trend more than does the evaporation from the natural grassland and desert. Stronger evaporation also significantly increases precipitation, potentially alleviating the stress of irrigation demands in arid regions. A series of sensitivity SCAM simulations indicate that a drier and warmer climate occurs with decreasing vegetation cover in the irrigated cropland region. Copyright © 2011 John Wiley & Sons, Ltd.

Dust Aerosol Important for Snowball Earth Deglaciation

Abstract Most previous global climate model simulations could only produce the termination of Snowball Earth episodes at CO2 partial pressures of several tenths of a bar, which is roughly an order of magnitude higher than recent estimates of CO2 levels during and shortly after Snowball events. These simulations have neglected the impact of dust aerosols on radiative transfer, which is an assumption of potentially grave importance. In this paper it is argued, using the Dust Entrainment and Deposition (DEAD) box model driven by GCM results, that atmospheric dust aerosol concentrations may have been one to two orders of magnitude higher during a Snowball Earth event than today. It is furthermore asserted on the basis of calculations using NCAR’s Single Column Atmospheric Model (SCAM)—a radiative–convective model with sophisticated aerosol, cloud, and radiative parameterizations—that when the surface albedo is high, such increases in dust aerosol loading can produce several times more surface warming than an increase in the partial pressure of CO2 from 10−4 to 10−1 bar. Therefore the conclusion is reached that including dust aerosols in simulations may reconcile the CO2 levels required for Snowball termination in climate models with observations.

Estimation of orographically induced wave drag in the stable boundary layer during the CASES-99 experimental campaign

This paper addresses the quantification of gravity wave drag due to small hills in the stable boundary layer. A single column atmospheric model is used to forecast wind and temperature profiles in the boundary layer. Next, these profiles are used to calculate vertical profiles of gravity wave drag. Climatology of wave drag magnitude and “wave drag events” is presented for the CASES-99 experimental campaign. It is found that gravity wave drag events occur for several relatively calm nights, and that the wave drag is then of equivalent magnitude as the turbulent drag. We also illustrate that wave drag events modify the wind speed sufficiently to substantially change the surface sensible heat flux.

Controls on the Activation and Strength of a High-Latitude Convective Cloud Feedback

Abstract Previous work has shown that a convective cloud feedback can greatly increase high-latitude surface temperature upon the removal of sea ice and can keep sea ice from forming throughout polar night. This feedback activates at increased greenhouse gas concentrations. It may help to explain the warm “equable climates” of the late Cretaceous and early Paleogene eras (∼100 to ∼35 million years ago) and may be relevant for future climate under global warming. Here, the factors that determine the critical threshold CO2 concentration at which this feedback is active and the magnitude of the warming caused by the feedback are analyzed using both a highly idealized model and NCAR’s single-column atmospheric model (SCAM) run under Arctic-like conditions. The critical CO2 is particularly important because it helps to establish the relevance of the feedback for past and future climates. Both models agree that increased heat flux into the high latitudes at low altitudes generally decreases the critical CO2. Increases in oceanic heat transport and in solar radiation absorbed during the summer should cause a sharp decrease in the critical CO2, but the effect of increases in atmospheric heat transport depends on its vertical distribution. It is furthermore found (i) that if the onset of convection produces more clouds and moisture, the critical CO2 should decrease, and the maximum temperature increase caused by the convective cloud feedback should increase and (ii) that reducing the depth of convection reduces the critical CO2 but has little effect on the maximum temperature increase caused by the convective cloud feedback. These results should help with interpretation of the strength and onset of the convective cloud feedback as found, for example, in Intergovernmental Panel on Climate Change (IPCC) coupled ocean–atmosphere models with different cloud and convection schemes.

Antarctic temperature at orbital timescales controlled by local summer duration

During the late Pleistocene epoch, proxies for Southern Hemisphere climate from the Antarctic ice cores vary nearly in phase with Northern Hemisphere insolation intensity at the precession and obliquity timescales. This coherence has led to the suggestion that Northern Hemisphere insolation controls Antarctic climate. However, it is unclear what physical mechanisms would tie southern climate to northern insolation. Here we call on radiative equilibrium estimates to show that Antarctic climate could instead respond to changes in the duration of local summer. Simple radiative equilibrium dictates that warmer annual average atmospheric temperatures occur as a result of a longer summer, as opposed to a more intense one, because temperature is more sensitive to insolation when the atmosphere is cooler. Furthermore, we show that a single-column atmospheric model reproduces this radiative equilibrium effect when forced exclusively by local Antarctic insolation, generating temperature variations that are coherent and in phase with proxies of Antarctic atmospheric temperature and surface conditions. We conclude that the duration of Southern Hemisphere summer is more likely to control Antarctic climate than the intensity of Northern Hemisphere summer with which it (often misleadingly) covaries. In our view, near interhemispheric climate symmetry at the obliquity and precession timescales arises from a northern response to local summer intensity and a southern response to local summer duration. On orbital timescales, Antarctic climate varies in phase with Northern Hemisphere insolation, but no physical mechanism for such a link is known. A new analysis suggests that at obliquity and precession timescales Antarctic climate may instead be responding to the duration of the local summer, which covaries with Northern insolation.

On the Land Surface–Atmosphere Coupling and Its Impact in a Single-Column Atmospheric Model

Abstract Three versions of the single-column European Centre for Medium-Range Weather Forecasts–Hamburg (ECHAM4) climate model are compared that differ either in the technique of the numerical coupling between land surface and atmosphere or the physical parameterization of the land surface processes. The standard ECHAM4 model utilizes a semi-implicit coupling technique between land surface and atmosphere in a way in which energy at the land surface–atmosphere interface is not conserved. This is a major deficiency. Two new model versions were developed: ECHAM4/IMPL and ECHAM4/SECHIBA. They incorporate an implicit coupling technique that conserves energy. ECHAM4 and ECHAM4/IMPL are identical with respect to all physical parameterizations they apply; the only difference is the coupling. In ECHAM4/SECHIBA, the ECHAM land surface scheme was replaced by SECHIBA (Schematisation des Echanges Hydriques a l’Interface entre la Biosphere et l’Atmosphere). The intercomparison of one-dimensional versions of these three...

Effect of Ocean Surface Heterogeneity on Climate Simulation

A sensitivity study is performed to examine the potential effect of spatial variations in sea surface temperature (SST) that typically are not resolved in general climate models (GCMs). The study uses a single-column atmospheric model, representing a grid box of a GCM, that overlies a surface domain divided into many subgrid cells. The model is driven by boundary conditions representative of the Gulf Stream off the mid-Atlantic coast of the United States, for the year 1987. A heterogeneous simulation, which includes subgrid spatial variability in SST, is contrasted with a homogeneous simulation, which assigns spatial mean SST to all cells. In summer, the presence of both stable and unstable surface layers in the heterogeneous domain causes heterogeneous–homogeneous differences in monthly, spatially averaged surface latent-heat flux of up to 47%. In contrast, in winter, the surface layer is unstable everywhere and heterogeneous–homogeneous differences in latent heat flux are smaller. Spatially averaged, surface sensible heat flux shows less influence of SST heterogeneity because this flux during summer is small. Further simulation suggests that a GCM can capture the effect of spatially varying boundary layer stability by resolving it just at the surface. The SST heterogeneity is also capable of driving sea-breeze-type circulations. Scale analysis suggests that typical resolution of contemporary climate GCMs will generally be insufficient to resolve these circulations.

Modelling the surface processes and the atmospheric boundary layer for semi-arid conditions

A simple parameterization of land-surface processes is tested for application in semi-dry areas. The surface scheme is included in the physical package of the Meteo-France atmospheric model ARPEGE. Its calibration using the EFEDA91 data set was necessary prior to mesoscale integrations of selected days of the field experiment. In order to model correctly the water budget and the energy balance over vineyards under dry soil conditions, the surface scheme was improved by parameterizing the vapor phase transfer in the soil and using two distinct roughness lengths for momentum and heat transfer. The introduction of the roughness length for heat is included in a surface boundary layer scheme, avoiding the classical iterative calculations of the heat transfer coefficient. Favourable results of tests of these modifications were found both for a time period of one month in stand-alone mode using an observed atmospheric forcing and for a diurnal cycle using a single column atmospheric model fully interactive with the surface scheme. Predictions of the surface temperature and of the sensible heat flux are significantly improved when a value of the roughness length for heat twenty times lower than the roughness length for momentum is used. Finally, the sensitivity of the predictions of the vertical development of the convective boundary layer to the value of the roughness lengths is examined.