Atmospheric Circulation Model Research Articles

Colder Siberian winters in a warming world

Climatology Winters have been more severe in Siberia over the past decade, even while loss of sea ice indicates dramatic warming of the Arctic. One hypothesis proposed to explain this apparent paradox is that Arctic sea ice loss forces a change in atmospheric circulation patterns that leads to colder Siberian winters. Using comprehensive atmospheric circulation models, Zhang et al. demonstrate that late autumn sea ice loss in the Barents-Kara Seas should result in a colder climate in Siberia the following winter. Their experiments also suggest that changes in the stratosphere, particularly shifts in and weakening of the stratospheric polar vortex owing to a reduction in sea ice, contribute substantially to the severity of winters in Siberia. Sci. Adv. 10.1126/sciadv.aat6025 (2018).

Evolutionary Exobiology II: investigating biological potential of synchronously-rotating worlds

AbstractPlanets that orbit M-class dwarf stars in their habitable zones are expected to become tidally-locked in the first billion years of their history. Simulations of potentially habitable planets orbiting K and G-class stars also suggest that many will become tidally-locked or become pseudo-synchronous rotators in a similar time frame where certain criteria are fulfilled. Simple models suggest that such planets will experience climatic regions organized in broadly concentric bands around the sub-stellar point, where irradiation is maximal. Here, we develop some of the quantitative, as well as the qualitative impacts of such climate on the evolutionary potential of life on such worlds, incorporating the effects of topography and ocean currents on potential biological diversity. By comparing atmospheric circulation models with terrestrial circulation and biological diversity, we are able to construct viable thought models of biological potential. While we await the generation of atmospheric circulation models that incorporate topography and varying subaerial landscape, these models can be used as a starting point to determine the overall evolutionary potential of such worlds. The planets in these thought-models have significant differences in their distribution of habitability that may not be apparent from simple climate modelling.

Age-dependent health risk from ambient air pollution: a modelling and data analysis of childhood mortality in middle-income and low-income countries

WHO estimates that, in 2015, nearly 1 million children younger than 5 years died from lower respiratory tract infections (LRIs). Ambient air pollution has a major impact on mortality from LRIs, especially in combination with undernutrition and inadequate health care. We aimed to estimate mortality due to ambient air pollution in 2015, particularly in children younger than 5 years, to investigate to what extent exposure to this risk factor affects life expectancy in different parts of the world. Applying results from a recent atmospheric chemistry-general circulation model and health statistics from the WHO Global Health Observatory, combined in integrated exposure-response functions, we updated our estimates of mortality from ambient (outdoor) air pollution. We estimated excess deaths attributable to air pollution by disease category and age group, particularly those due to ambient air pollution-induced LRIs (AAP-LRIs) in childhood. Estimates are presented as excess mortality attributable to ambient air pollution and years of life lost (YLLs). To study recent developments, we calculated our estimates for the years 2010 and 2015. Overall, 4·55 million deaths (95% CI 3·41 million to 5·56 million) were attributable to air pollution in 2015, of which 727 000 deaths (573 000-865 000) were due to AAP-LRIs. We estimated that AAP-LRIs caused about 237 000 (192 000-277 000) excess child deaths in 2015. Although childhood AAP-LRIs contributed about 5% of air pollution-attributable deaths worldwide, they accounted for 18% of losses in life expectancy, equivalent to 21·5 million (17 million to 25 million) of the total 122 million YLLs due to ambient air pollution in 2015. The mortality rate from ambient air pollution was highest in Asia, whereas the per capita YLLs were highest in Africa. We estimated that in sub-Saharan Africa, ambient air pollution reduces the average life expectancy of children by 4-5 years. In Asia, all-age mortality increased by about 10% between 2010 and 2015, whereas childhood mortality from AAP-LRIs declined by nearly 30% in the same period. Most child deaths due to AAP-LRIs occur in low-income countries in Africa and Asia. A three-pronged strategy is needed to reduce the health effects of ambient air pollution in children: aggressive reduction of air pollution levels, improvements in nutrition, and enhanced treatment of air pollution-related health outcomes. None.

Arctic warming induced by the Laurentide Ice Sheet topography

Abstract. It is well known that ice sheet–climate feedbacks are essential for realistically simulating the spatiotemporal evolution of continental ice sheets over glacial–interglacial cycles. However, many of these feedbacks are dependent on the ice sheet thickness, which is poorly constrained by proxy data records. For example, height estimates of the Laurentide Ice Sheet (LIS) topography at the Last Glacial Maximum (LGM; ∼ 21 000 years ago) vary by more than 1 km among different ice sheet reconstructions. In order to better constrain the LIS elevation it is therefore important to understand how the mean climate is influenced by elevation discrepancies of this magnitude. Here we use an atmospheric circulation model coupled to a slab-ocean model to analyze the LGM surface temperature response to a broad range of LIS elevations (from 0 to over 4 km). We find that raising the LIS topography induces a widespread surface warming in the Arctic region, amounting to approximately 1.5 ∘C per km of elevation increase, or about 6.5 ∘C for the highest LIS. The warming is attributed to an increased poleward energy flux by atmospheric stationary waves, amplified by surface albedo and water vapor feedbacks, which account for about two-thirds of the total temperature response. These results suggest a strong feedback between continental-scale ice sheets and the Arctic temperatures that may help constrain LIS elevation estimates for the LGM and explain differences in ice distribution between the LGM and earlier glacial periods.

Titan's Meteorology Over the Cassini Mission: Evidence for Extensive Subsurface Methane Reservoirs

AbstractCassini observations of Titan's weather patterns over >13 years, almost half a Saturnian year, provide insight into seasonal circulation patterns and the methane cycle. The Imaging Science Subsystem and the Visual and Infrared Mapping Spectrometer documented cloud locations, characteristics, morphologies, and behavior. Clouds were generally more prevalent in the summer hemisphere, but there were surprises in locations and timing of activity: Southern clouds were common at midlatitudes, northern clouds initially appeared much sooner than model predictions, and north polar summer convective systems did not appear before the mission ended. Differences from expectations constrain atmospheric circulation models, revealing factors that best match observations, including the roles of surface and subsurface reservoirs. The preference for clouds at mid‐northern latitudes rather than near the pole is consistent with models that include widespread polar near‐surface methane reservoirs in addition to the lakes and seas, suggesting a broader subsurface methane table is accessible to the atmosphere.

Potential impacts of climate change on groundwater levels on the Kerdi-Shirazi plain, Iran

It is important to predict how groundwater levels in an aquifer will respond to various climate change scenarios to effectively plan for how groundwater resources will be used in the future. Due to the overuse of groundwater resources and the multi-year drought in the Kerdi-Shirazi plain in Iran, some land subsidence and a drop in groundwater levels has taken place, and without active management, further degradation of the groundwater resource is possible under predicted future climate change scenarios in the country. To determine the potential impacts of climate change on groundwater levels in the region, the groundwater model GMS was coupled with the atmospheric circulation model HADCM3 using scenarios A1B, A2 and B1 for the period 2016–2030. The results of the climate modelling suggest that the Kerdi-Shirazi plain will experience an increase in minimum temperature and maximum temperature of, respectively, between 0.03 and 0.47, and 0.32–0.45 °C for this time period. The results of the groundwater modelling suggest that water levels on the Kerdi-Shirazi plain will continue to decline over the forecast period with decreases of 34.51, 36.57 and 33.58 m being predicted, respectively, for climate scenarios A1B, A2 and B1. Consequently, groundwater resources in the Kerdi-Shirazi plain will urgently need active management to minimize the effects of ongoing water level decline and to prevent saltwater intrusion and desertification in the region.

Superrotation on Venus, on Titan, and Elsewhere

The superrotation of the atmospheres of Venus and Titan has puzzled dynamicists for many years and seems to put these planets in a very different dynamical regime from most other planets. In this review, we consider how to define superrotation objectively and explore the constraints that determine its occurrence. Atmospheric superrotation also occurs elsewhere in the Solar System and beyond, and we compare Venus and Titan with Earth and other planets for which wind estimates are available. The extreme superrotation on Venus and Titan poses some difficult challenges for numerical models of atmospheric circulation, much more difficult than for more rapidly rotating planets such as Earth or Mars. We consider mechanisms for generating and maintaining a superrotating state, all of which involve a global meridional overturning circulation. The role of nonaxisymmetric eddies is crucial, however, but the detailed mechanisms may differ between Venus, Titan, and other planets.

From global circulation to local flood loss: Coupling models across the scales

Comprehensive flood risk modeling is crucial for understanding, assessing, and mitigating flood risk. Modeling extreme events is a well-established practice in the atmospheric and hydrological sciences and in the insurance industry. Several specialized models are used to research extreme events including atmospheric circulation models, hydrological models, hydrodynamic models, and damage and loss models. Although these model types are well established, and coupling two to three of these models has been successful, no assessment of a full and comprehensive model chain from the atmospheric to local scale flood loss models has been conducted. The present study introduces a model chain setup incorporating a GCM/RCM to model atmospheric processes, a hydrological model to estimate the catchment's runoff reaction to precipitation inputs, a hydrodynamic model to identify flood-affected areas, and a damage and loss model to estimate flood losses. Such coupling requires building interfaces between the individual models that are coherent in terms of spatial and temporal resolution and therefore calls for several pre- and post-processing steps for the individual models as well as for a computationally efficient strategy to identify and model extreme events. The results show that a coupled model chain allows for good representation of runoff for both long-term runoff characteristics and extreme events, provided a bias correction on precipitation input is applied. While the presented approach for deriving loss estimations for particular extreme events leads to reasonable results, two issues have been identified that need to be considered in further applications: (i) the identification of extreme events in long-term GCM simulations for downscaling and (ii) the representativeness of the vulnerability functions for local conditions.

Scale-Invariant Formulation of Momentum Diffusion for High-Resolution Atmospheric Circulation Models

A new version of the dynamic Smagorinsky model is presented that applies for nonisotropic momentum diffusion in high-resolution atmospheric circulation models. While the horizontal mixing length is computed in accordance with scale invariance in the mesoscale regime of the horizontal energy cascade, the associated dynamic vertical mixing length (DVML) is based on a recently developed scale invariance criterion and represents an application of the scaling laws of stratified macroturbulence. The DVML is validated in high-resolution simulations with the Kühlungsborn mechanistic general circulation model, using triangular spectral truncation at wavenumber 330 and a vertical level spacing of about 200 m in the upper troposphere. For a proper choice of the test filter, the model simulates a realistic horizontal kinetic energy spectrum in the troposphere along with a realistic intensity of the Lorenz energy cycle. This result is obtained without any hyperdiffusion, and it depends only little on whether the vertical mixing length is prescribed or set to the DVML. The globally averaged Smagorinsky parameter is about c S ≅ 0.53. The latitude–height cross sections show that c S maximizes in regions of strong mesoscale kinetic energy.

Environmental impact assessment for climate change policy with the simulation-based integrated assessment model E3ME-FTT-GENIE

A high degree of consensus exists in the climate sciences over the role that human interference with the atmosphere is playing in changing the climate. Following the Paris Agreement, a similar consensus exists in the policy community over the urgency of policy solutions to the climate problem. The context for climate policy is thus moving from agenda setting, which has now been mostly established, to impact assessment, in which we identify policy pathways to implement the Paris Agreement. Most integrated assessment models currently used to address the economic and technical feasibility of avoiding climate change are based on engineering perspectives with a normative systems optimisation philosophy, suitable for agenda setting, but unsuitable to assess the socio-economic impacts of realistic baskets of climate policies. Here, we introduce a fully descriptive, simulation-based integrated assessment model designed specifically to assess policies, formed by the combination of (1) a highly disaggregated macro-econometric simulation of the global economy based on time series regressions (E3ME), (2) a family of bottom-up evolutionary simulations of technology diffusion based on cross-sectional discrete choice models (FTT), and (3) a carbon cycle and atmosphere circulation model of intermediate complexity (GENIE). We use this combined model to create a detailed global and sectoral policy map and scenario that sets the economy on a pathway that achieves the goals of the Paris Agreement with >66% probability of not exceeding 2 °C of global warming. We propose a blueprint for a new role for integrated assessment models in this upcoming policy assessment context.

Influences of large-scale convection and moisture source on monthly precipitation isotope ratios observed in Thailand, Southeast Asia

Many paleoclimatic records in Southeast Asia rely on rainfall isotope ratios as proxies for past hydroclimatic variability. However, the physical processes controlling modern rainfall isotopic behaviors in the region is poorly constrained. Here, we combined isotopic measurements at six sites across Thailand with an isotope-incorporated atmospheric circulation model (IsoGSM) and the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model to investigate the factors that govern the variability of precipitation isotope ratios in this region. Results show that rainfall isotope ratios are both correlated with local rainfall amount and regional outgoing longwave radiation, suggesting that rainfall isotope ratios in this region are controlled not only by local rain amount (amount effect) but also by large-scale convection. As a transition zone between the Indian monsoon and the western North Pacific monsoon, the spatial difference of observed precipitation isotope among different sites are associated with moisture source. These results highlight the importance of regional processes in determining rainfall isotope ratios in the tropics and provide constraints on the interpretation of paleo-precipitation isotope records in the context of regional climate dynamics.

Forecast of Polar Stratospheric Vortex Dynamics Using the SL-AV Global Atmosphere Model

The quality of Arctic winter stratospheric dynamics forecast using the SL-AV atmospheric global circulation model is studied. The series of numerical experiments show that forecasts with the lead time up to 7 days are successful. Zonal wind reversal during minor sudden stratospheric warmings is predicted 10–11 days ahead. Overall, the situations of strong polar jet disturbances are beneficial for the forecast accuracy.

Actinometric System Aboard the Yak-42D “Roshydromet” Research Aircraft

The actinometric system installed aboard the Yak-42D "Roshydromet" research aircraft is presented. It is designed to study radiation processes in the troposphere. The system is based on standard Kipp&Zonen actinometric instruments for measuring solar, thermal, and ultraviolet radiation fluxes as well as on specially developed radiation models with high-precision methods for solving radiative transfer equations (Monte Carlo, k-distribution, and line-by-line calculations). The combination of actinometric measurements and detailed simulation of radiative transfer in the atmosphere allows examining the radiation balance components throughout the troposphere using in situ measurements at the aircraft location. Some results of studying radiation fluxes obtained during the flights over the Arctic region of the Russian Federation are presented. The data of measurements carried out using the presented system are useful for validating radiation codes utilized in general atmospheric circulation models and for processing satellite remote sensing data.

Cloud Atlas: Rotational Modulations in the L/T Transition Brown Dwarf Companion HN Peg B

Abstract Time-resolved observations of brown dwarfs’ rotational modulations provide powerful insights into the properties of condensate clouds in ultra-cool atmospheres. Multi-wavelength light curves reveal cloud vertical structures, condensate particle sizes, and cloud morphology, which directly constrain condensate cloud and atmospheric circulation models. We report results from Hubble Space Telescope/Wide Field Camera 3 near-infrared G141 taken in six consecutive orbits observations of HN Peg B, an L/T transition brown dwarf companion to a G0V type star. The best-fit sine wave to the 1.1–1.7 μm broadband light curve has an amplitude of 1.206% ± 0.025% and period of 15.4 ± 0.5 hr. The modulation amplitude has no detectable wavelength dependence except in the 1.4 μm water absorption band, indicating that the characteristic condensate particle sizes are large (>1 μm). We detect significantly (4.4σ) lower modulation amplitude in the 1.4 μm water absorption band and find that HN Peg B’s spectral modulation resembles those of early T type brown dwarfs. We also describe a new empirical interpolation method to remove spectral contamination from the bright host star. This method may be applied in other high-contrast time-resolved observations with WFC3.

Statistical analysis of inertial gravity wave parameters in the lower stratosphere over Northern China

To determine the morphology of inertial gravity wave (IGW) activity in the lower stratosphere (18–25 km) over Northern China and provide observational data constraints for IGW parameterization in atmospheric circulation models, the seasonal variation and longitudinal distribution of IGW parameters were analyzed statistically using 4 years (2010–2013) of radiosonde data from 20 sites distributed throughout Northern China (80.2°E–122.3°E). The results are as follows. (1) The seasonal variation in the monthly mean IGW energy (strong in winter and weak in summer) is consistent with the results for other regions in the Northern Hemisphere. However, the energy shows a significant longitudinal increase from west to east in winter and the opposite pattern in summer, which has rarely been reported. (2) The monthly mean intrinsic frequency exhibits clear seasonal variation (large in winter and small in summer). The annual average ratio with the Coriolis frequency is 2.47, while the degree of polarization exhibits the opposite seasonal variation, with an annual average of 0.71. The monthly mean vertical and horizontal wavelengths are 2.5 and 481.3 km in Northern China, respectively. (3) The annual mean magnitude of the intrinsic horizontal group speed (7.0 m/s) is much larger than that of the vertical group speed (0.08 m/s), and both have maxima in winter and minima in summer. The frequency of occurrence of the westward-propagated IGW is larger than that of the eastward-propagated IGW year round, and it is isotropic in the north–south direction. This phenomenon is related to the filtering effect of the tropospheric westerly jet. The annual mean fraction of upward propagation is 75.9%, with a minimum in winter. (4) The momentum flux exhibits a similar temporal and spatial distribution to energy, showing preferred propagation in the northwest direction. (5) The correlation of the monthly mean total energy of the IGW with the westerly jet and the dynamic instability were studied. The results suggest that the westerly jet near the tropopause has a strong influence on the IGWs activity in the lower stratosphere in Northern China and the height region of the westerly jet is a possible source region for IGWs, the maxima regions of the occurrence rates of dynamic instability at the upper and lower edges of the westerly jet in winter are also the possible source region for IGWs.

Uniform-in-Time Error Estimates for the Postprocessing Galerkin Method Applied to a Data Assimilation Algorithm

We apply the postprocessing Galerkin method to a recently introduced continuous data assimilation (downscaling) algorithm for obtaining a numerical approximation of the solution of the two-dimensional Navier--Stokes equations corresponding to given measurements from a coarse spatial mesh. Under suitable conditions on the relaxation (nudging) parameter, the resolution of the coarse spatial mesh, and the resolution of the numerical scheme, we obtain uniform-in-time estimates for the error between the numerical approximation given by the postprocessing Galerkin method and the reference solution corresponding to the measurements. Our results are valid for a large class of interpolant operators, including low Fourier modes and local averages over finite volume elements. Notably, we use here the two-dimensional Navier--Stokes equations as a paradigm, but our results apply equally to other evolution equations, such as the Boussinesq system of Benard convection and other oceanic and atmospheric circulation models.

The Novaya Zemlya Bora: Analysis and Numerical Modeling

We consider the data of an ASRI reanalysis to distinguish the properties of velocity and temperature fields in the region of Novaya Zemlya (NZ). A numerical simulation of the bora development is performed using the WRF-ARW regional model of atmospheric circulation for two cases with different directions of the wind. In the case of southeastern winds, the wind speed and temperature fields are reproduced and the characteristics of the bora are defined: temperature and wind speed increase over the lee slope of mountains and coastal western area of the Barents Sea. In the case of a western wind, the bora does not appear. The estimates of temperature contrasts in the flow of the air stream over the NZ mountains found in the processing of the ASRI data are reported. The region of high velocities and fluxes of sensible and latent heat indicating the climatic role of the NZ archipelago noted earlier in [12] is determined.

Extratropical Response to the MJO: Nonlinearity and Sensitivity to the Initial State

Previous studies have shown that the Madden–Julian oscillation (MJO) has a global impact that may provide an important source of skill for subseasonal predictions. The extratropical response was found to be the strongest when the tropical diabatic heating has a dipole structure with convection anomaly centers of opposite sign in the eastern Indian Ocean and the western Pacific. A positive (negative) MJO dipole heating refers to that with heating (cooling) in the eastern Indian Ocean and cooling (heating) in the western Pacific. In this study, two aspects of the extratropical response to the MJO are examined: 1) nonlinearity, which answers the question of whether the response to a positive MJO dipole heating is the mirror image of that to a negative MJO, and 2) sensitivity to the initial state, which explores the dependence of the extratropical response on the initial condition of the westerly jet. Ensemble integrations using a primitive-equation global atmospheric circulation model are performed with anomalous tropical thermal forcings that resemble a positive MJO (+MJO) and a negative MJO (−MJO). The response in the first week is largely linear. After that, significant asymmetry is found between the response in the positive MJO and the negative MJO. The 500-hPa negative geopotential height response in the North Pacific of the −MJO run is located about 30° east of the positive height response of the +MJO run. There is also an eastward shift of the extratropical wave train in the Pacific–North American region. This simulated nonlinearity is in agreement with the observations. The two leading response patterns among the ensemble members are identified by an empirical orthogonal function (EOF) analysis. EOF1 represents an eastward shift of the wave train, which is positively correlated with strengthening of the East Asian subtropical upper-troposphere westerly jet in the initial condition. On the other hand, EOF2 represents an amplification of the response, which is associated with a southward shift of the westerly jet in the initial state.

Numerical Simulation of the Novaya Zemlya Bora

The development of the bora in case of strong southeastern wind in the area of Novaya Zemlya in the winter-spring of 2016 is simulated using the WRF-ARW numerical atmosphere circulation model with high spatial resolution. The features of wind speed and air temperature fields are considered which define the formation of the intensive near-surface flow, the bora, over the lee western slope of the mountain range. It is demonstrated that the bora development leads to the air temperature rise over the eastern part of the Barents Sea, to the increased surface heat fluxes, and to the formation of the cloudless zone over the sea westward of Novaya Zemlya. It was found that the main reason for the bora development is the high stability of the atmospheric boundary layer over the Kara Sea. It is shown that in case of western wind the Novaya Zemlya archipelago does not exert considerable influence on the air exchange in the Kara Sea area.

Modeling the Effects of Inhomogeneous Aerosols on the Hot Jupiter Kepler-7b’s Atmospheric Circulation

Abstract Motivated by observational evidence of inhomogeneous clouds in exoplanetary atmospheres, we investigate how proposed simple cloud distributions can affect atmospheric circulations and infrared emission. We simulated temperatures and winds for the hot Jupiter Kepler-7b using a three-dimensional atmospheric circulation model that included a simplified aerosol radiative transfer model. We prescribed fixed cloud distributions and scattering properties based on results previously inferred from Kepler-7b optical phase curves, including inhomogeneous aerosols centered along the western terminator and hypothetical cases in which aerosols additionally extended across much of the planet’s nightside. In all cases, a strong jet capable of advecting aerosols from a cooler nightside to dayside was found to persist, but only at the equator. Colder temperatures at mid and polar latitudes might permit aerosol to form on the dayside without the need for advection. By altering the deposition and redistribution of heat, aerosols along the western terminator produced an asymmetric heating that effectively shifts the hottest spot further east of the substellar point than expected for a uniform distribution. The addition of opaque high clouds on the nightside can partly mitigate this enhanced shift by retaining heat that contributes to warming west of the hotspot. These expected differences in infrared phase curves could place constraints on proposed cloud distributions and their infrared opacities for brighter hot Jupiters.