scholarly journals Response of Upper Clouds in Global Warming Experiments Obtained Using a Global Nonhydrostatic Model with Explicit Cloud Processes

2012 ◽  
Vol 25 (6) ◽  
pp. 2178-2191 ◽  
Author(s):  
Masaki Satoh ◽  
Shin-ichi Iga ◽  
Hirofumi Tomita ◽  
Yoko Tsushima ◽  
Akira T. Noda
Keyword(s):  
Global Warming ◽  
Mass Flux ◽  
Cloud Cover ◽  
Large Scale ◽  
Cloud Microphysics ◽  
Microphysics Scheme ◽  
Nonhydrostatic Model ◽  
The Tropics ◽  
Ice Water ◽  
Convective Mass Flux

Abstract Using a global nonhydrostatic model with explicit cloud processes, upper-cloud changes are investigated by comparing the present climate condition under the perpetual July setting and the global warming condition, in which the sea surface temperature (SST) is raised by 2°. The sensitivity of the upper-cloud cover and the ice water path (IWP) are investigated through a set of experiments. The responses of convective mass flux and convective areas are also examined, together with those of the large-scale subsidence and relative humidity in the subtropics. The responses of the IWP and the upper-cloud cover are found to be opposite; that is, as the SST increases, the IWP averaged over the tropics decreases, whereas the upper-cloud cover in the tropics increases. To clarify the IWP response, a simple conceptual model is constructed. The model consists of three columns of deep convective core, anvil, and environmental subsidence regions. The vertical profiles of hydrometers are predicted with cloud microphysics processes and kinematically prescribed circulation. The reduction in convective mass flux is found to be a primary factor in the decrease of the IWP under the global warming condition. Even when a different and more comprehensive cloud microphysics scheme is used, the reduction in the IWP due to the mass flux change is also confirmed.

Improvement of a Cloud Microphysics Scheme for a Global Nonhydrostatic Model Using TRMM and a Satellite Simulator

2017 ◽  
Vol 74 (1) ◽  
pp. 167-184 ◽  
Author(s):  
Woosub Roh ◽  
Masaki Satoh ◽  
Tomoe Nasuno
Keyword(s):  
Joint Probability ◽  
Tropical Rainfall Measuring Mission ◽  
Atmospheric Model ◽  
Cloud Microphysics ◽  
Horizontal Resolution ◽  
Microphysics Scheme ◽  
Tropical Ocean ◽  
Nonhydrostatic Model ◽  
Joint Histogram ◽  
The Tropics

Abstract The cloud and precipitation simulated by a global nonhydrostatic model with a 3.5-km horizontal resolution, the Nonhydrostatic Icosahedral Atmospheric Model (NICAM), are evaluated using the Tropical Rainfall Measuring Mission (TRMM) and a satellite simulator. A previous study by Roh and Satoh evaluated the single-moment bulk microphysics and established the modified microphysics scheme for the specific tropical open ocean using a regional version of NICAM. In this study, the authors expanded the evaluation over the entire tropics and parts of the midlatitude areas (20°–36°S, 20°–36°N) using a joint histogram of the cloud-top temperature and precipitation echo-top heights and contoured frequency by altitude diagrams of the deep convective systems. The modified microphysics simulation improves the joint probability density functions of the cloud-top temperatures and precipitation cloud-top heights over not only the tropical ocean but also the land and midlatitude areas. Compared with the default microphysics simulation, the modified microphysics simulation shows a clearer distinction between the land and ocean in the tropics, which is related to the contrast between the shallow and the deep clouds. In addition, the two microphysics simulation methods were also compared over the tropics using joint histograms of the cloud-top and precipitation cloud-top heights on the basis of CloudSat measurements. It was found that the microphysics scheme that was modified for the tropical ocean displayed general cloud and precipitation improvements in the global domain over the tropics.

scholarly journals Response of Ice and Liquid Water Paths of Tropical Cyclones to Global Warming Simulated by a Global Nonhydrostatic Model with Explicit Cloud Microphysics

2013 ◽  
Vol 26 (24) ◽  
pp. 9931-9945 ◽  
Author(s):  
Yohei Yamada ◽  
Masaki Satoh
Keyword(s):  
Global Warming ◽  
Tropical Cyclones ◽  
Liquid Water ◽  
Cloud Microphysics ◽  
Future Climate ◽  
Cumulus Parameterization ◽  
Simulation Data ◽  
Nonhydrostatic Model ◽  
Ice Water ◽  
Future Climate Projection

Abstract Cloud feedback plays a key role in the future climate projection. Using global nonhydrostatic model (GNHM) simulation data for a present-day [control (CTL)] and a warmer [global warming (GW)] experiment, the authors estimate the contribution of tropical cyclones (TCs) to ice water paths (IWP) and liquid water paths (LWP) associated with TCs and their changes between CTL and GW experiments. They use GNHM with a 14-km horizontal mesh for explicitly calculating cloud microphysics without cumulus parameterization. This dataset shows that the cyclogenesis under GW conditions reduces to approximately 70% of that under CTL conditions, as shown in a previous study, and the tropical averaged IWP (LWP) is reduced by approximately 2.76% (0.86%). Horizontal distributions of IWP and LWP changes seem to be closely related to TC track changes. To isolate the contributions of IWP/LWP associated with TCs, the authors first examine the radial distributions of IWP/LWP from the TC center at their mature stages and find that they generally increase for more intense TCs. As the intense TC in GW increases, the IWP and LWP around the TC center in GW becomes larger than that in CTL. The authors next define the TC area as the region within 500 km from the TC center at its mature stages. They find that the TC’s contribution to the total tropical IWP (LWP) is 4.93% (3.00%) in CTL and 5.84% (3.69%) in GW. Although this indicates that the TC’s contributions to the tropical IWP/LWP are small, IWP/LWP changes in each basin behave in a manner similar to those of the cyclogenesis and track changes under GW.

scholarly journals Responses of Clouds and Large‐Scale Circulation to Global Warming Evaluated From Multidecadal Simulations Using a Global Nonhydrostatic Model

2019 ◽  
Vol 11 (9) ◽  
pp. 2980-2995 ◽  
Author(s):  
Akira T. Noda ◽  
Chihiro Kodama ◽  
Yohei Yamada ◽  
Masaki Satoh ◽  
Tomoo Ogura ◽  
...  
Keyword(s):  
Global Warming ◽  
Large Scale ◽  
Large Scale Circulation ◽  
Nonhydrostatic Model

Spatial Patterns of Precipitation Change in CMIP5: Why the Rich Do Not Get Richer in the Tropics

2013 ◽  
Vol 26 (11) ◽  
pp. 3803-3822 ◽  
Author(s):  
Robin Chadwick ◽  
Ian Boutle ◽  
Gill Martin
Keyword(s):  
Spatial Patterns ◽  
Mass Flux ◽  
Precipitation Change ◽  
Specific Humidity ◽  
Tropical Precipitation ◽  
Humidity Change ◽  
The Rich ◽  
Convergence Zones ◽  
The Tropics ◽  
Convective Mass Flux

Abstract Changes in the patterns of tropical precipitation (P) and circulation are analyzed in Coupled Model Intercomparison Project phase 5 (CMIP5) GCMs under the representative concentration pathway 8.5 (RCP8.5) scenario. A robust weakening of the tropical circulation is seen across models, associated with a divergence feedback that acts to reduce convection most in areas of largest climatological ascent. This is in contrast to the convergence feedback seen in interannual variability of tropical precipitation patterns. The residual pattern of convective mass-flux change is associated with shifts in convergence zones due to mechanisms such as SST gradient change, and this is often locally larger than the weakening due to the divergence feedback. A simple framework is constructed to separate precipitation change into components based on different mechanisms and to relate it directly to circulation change. While the tropical mean increase in precipitation is due to the residual between the positive thermodynamic change due to increased specific humidity and the decreased convective mass flux due to the weakening of the circulation, the spatial patterns of these two components largely cancel each other out. The rich-get-richer mechanism of greatest precipitation increases in ascent regions is almost negated by this cancellation, explaining why the spatial correlation between climatological P and the climate change anomaly ΔP is only 0.2 over the tropics for the CMIP5 multimodel mean. This leaves the spatial pattern of precipitation change to be dominated by the component associated with shifts in convergence zones, both in the multimodel mean and intermodel uncertainty, with the component due to relative humidity change also becoming important over land.

scholarly journals The multi-scale aerosol-climate model PNNL-MMF: model description and evaluation

2010 ◽  
Vol 3 (4) ◽  
pp. 1625-1695 ◽  
Author(s):  
M. Wang ◽  
S. Ghan ◽  
R. Easter ◽  
M. Ovchinnikov ◽  
X. Liu ◽  
...  
Keyword(s):  
Reasonable Agreement ◽  
Large Scale ◽  
Climate Model ◽  
Cloud Microphysics ◽  
Chemical Processes ◽  
Future Climate Change ◽  
Free Troposphere ◽  
Microphysics Scheme ◽  
New Model ◽  
Multi Scale

Abstract. Anthropogenic aerosol effects on climate produce one of the largest uncertainties in estimates of radiative forcing of past and future climate change. Much of this uncertainty arises from the multi-scale nature of the interactions between aerosols, clouds and large-scale dynamics, which are difficult to represent in conventional global climate models (GCMs). In this study, we develop a multi-scale aerosol climate model that treats aerosols and clouds across different scales, and evaluate the model performance, with a focus on aerosol treatment. This new model is an extension of a multi-scale modeling framework (MMF) model that embeds a cloud-resolving model (CRM) within each grid column of a GCM. In this extension, the effects of clouds on aerosols are treated by using an explicit-cloud parameterized-pollutant (ECPP) approach that links aerosol and chemical processes on the large-scale grid with statistics of cloud properties and processes resolved by the CRM. A two-moment cloud microphysics scheme replaces the simple bulk microphysics scheme in the CRM, and a modal aerosol treatment is included in the GCM. With these extensions, this multi-scale aerosol-climate model allows the explicit simulation of aerosol and chemical processes in both stratiform and convective clouds on a global scale. Simulated aerosol budgets in this new model are in the ranges of other model studies. Simulated gas and aerosol concentrations are in reasonable agreement with observations, although the model underestimates black carbon concentrations at the surface. Simulated aerosol size distributions are in reasonable agreement with observations in the marine boundary layer and in the free troposphere, while the model underestimates the accumulation mode number concentrations near the surface, and overestimates the accumulation number concentrations in the free troposphere. Simulated cloud condensation nuclei (CCN) concentrations are within the observational variations. Simulated aerosol optical depth (AOD) and single scattering albedo (SSA) are in reasonable agreement with observations, and the spatial distribution of AOD is consistent with observations, while the model underestimates AOD over regions with strong fossil fuel and biomass burning emissions, and overestimates AOD over regions with strong dust emissions. Overall, this multi-scale aerosol climate model simulates aerosol fields as well as conventional aerosol models.

scholarly journals Estimating the Shallow Convective Mass Flux from the Subcloud-Layer Mass Budget

2020 ◽  
Vol 77 (5) ◽  
pp. 1559-1574 ◽  
Author(s):  
Raphaela Vogel ◽  
Sandrine Bony ◽  
Bjorn Stevens
Keyword(s):  
Vertical Velocity ◽  
Diurnal Cycle ◽  
Mass Flux ◽  
Large Scale ◽  
Cloud Base ◽  
Entrainment Rate ◽  
Field Campaign ◽  
Mass Budget ◽  
Convective Mixing ◽  
Convective Mass Flux

Abstract This paper develops a method to estimate the shallow-convective mass flux M at the top of the subcloud layer as a residual of the subcloud-layer mass budget. The ability of the mass-budget estimate to reproduce the mass flux diagnosed directly from the cloud-core area fraction and vertical velocity is tested using real-case large-eddy simulations over the tropical Atlantic. We find that M reproduces well the magnitude, diurnal cycle, and day-to-day variability of the core-sampled mass flux, with an average root-mean-square error of less than 30% of the mean. The average M across the four winter days analyzed is 12 mm s−1, where the entrainment rate E contributes on average 14 mm s−1 and the large-scale vertical velocity W contributes −2 mm s−1. We find that day-to-day variations in M are mostly explained by variations in W, whereas E is very similar among the different days analyzed. Instead E exhibits a pronounced diurnal cycle, with a minimum of about 10 mm s−1 around sunset and a maximum of about 18 mm s−1 around sunrise. Application of the method to dropsonde data from an airborne field campaign in August 2016 yields the first measurements of the mass flux derived from the mass budget, and supports the result that the variability in M is mostly due to the variability in W. Our analyses thus suggest a strong coupling between the day-to-day variability in shallow convective mixing (as measured by M) and the large-scale circulation (as measured by W). Application of the method to the EUREC4A field campaign will help evaluate this coupling, and assess its implications for cloud-base cloudiness.

scholarly journals A Moist Conceptual Model for the Boundary Layer Structure and Radiatively Driven Shallow Circulations in the Trades

2019 ◽  
Vol 76 (5) ◽  
pp. 1289-1306 ◽  
Author(s):  
Ann Kristin Naumann ◽  
Bjorn Stevens ◽  
Cathy Hohenegger
Keyword(s):  
Boundary Layer ◽  
Conceptual Model ◽  
Mass Flux ◽  
Large Scale ◽  
Layer Structure ◽  
Radiative Cooling ◽  
Shallow Convection ◽  
Tropical Oceans ◽  
Moderate Range ◽  
Convective Mass Flux

Abstract A conceptual model is developed to analyze how radiative cooling and the effect of moisture and shallow convection modify the boundary layer (BL) structure and the strength of mesoscale shallow circulations. The moist BL allows for a convective mass flux to modify the BL mass balance, which enhances inversion entrainment compared to a dry case and acts as a moisture valve to the BL. The convective mass flux is found to be insensitive to the applied radiative cooling and in the absence of heterogeneities cloud-free conditions exist only for unusual large-scale forcings. The model is able to explain the moderate range of BL heights and humidities observed in the trades. In a two-column setup, differential radiative BL cooling causes a pressure difference, which drives a BL flow from the cold and moist column to the warm and dry column and couples them dynamically. The small inversion buoyancy jump of the moist BL yields a stronger BL flow of 4 m s−1 instead of 1 m s−1 in the dry case. For typical conditions of the subsidence-dominated tropical oceans, a radiatively driven shallow circulation is stronger than one driven by sea surface temperature (SST) gradients. While the strength of the SST-driven circulation decreases with decreasing SST difference, the radiatively driven circulation is insensitive to the radiative BL cooling difference. In both cases, convection is suppressed in the descending branch of the shallow circulation and enhanced in the ascending branch, resembling patterns of organized shallow convection.

Measuring shallow convective mass flux profiles in the trade wind region

2021 ◽  
Author(s):  
Marcus Klingebiel ◽  
Heike Konow ◽  
Bjorn Stevens
Keyword(s):  
Mass Flux ◽  
Large Scale ◽  
Doppler Radar ◽  
Cloud Base ◽  
Trade Wind ◽  
Doppler Lidar ◽  
Shallow Convection ◽  
Lidar Measurements ◽  
Flux Profile ◽  
Convective Mass Flux

AbstractMass flux is a key quantity in parameterizations of shallow convection. To estimate the shallow convective mass flux as accurately as possible, and to test these parameterizations, observations of this parameter are necessary. In this study, we show how much the mass flux varies and how this can be used to test factors that may be responsible for its variation. Therefore, we analyze long term Doppler radar and Doppler lidar measurements at the Barbados Cloud Observatory over a time period of 30 months, which results in a mean mass flux profile with a peak value of 0.03 kg m−2 s−1 at an altitude of ~730 m, similar to observations from Ghate et al. (2011) at the Azores Islands. By combining Doppler radar and Doppler lidar measurements, we find that the cloud base mass flux depends mainly on the cloud fraction and refutes an idea based on large eddy simulations, that the velocity scale is in major control of the shallow cumulus mass flux. This indicates that the large scale conditions might play a more important role than what one would deduce from simulations using prescribed large-scale forcings.

scholarly journals A Simple Model of a Balanced Boundary Layer Coupled to a Large-Scale Convective Circulation

2019 ◽  
Vol 76 (3) ◽  
pp. 837-849
Author(s):  
Robert J. Beare ◽  
Michael J. P. Cullen
Keyword(s):  
Boundary Layer ◽  
Simple Model ◽  
Surface Temperature ◽  
Mass Flux ◽  
Time Scale ◽  
Large Scale ◽  
Climate Models ◽  
Convective Boundary ◽  
Convective Circulation ◽  
Convective Mass Flux

Abstract Many simple models of large-scale tropical circulations do not include a frictional boundary layer. A simple model is presented where the convective circulation is coupled to the boundary layer convergence. In the free troposphere, convection and boundary layer heating try to relax to a moist adiabat from the local sea surface temperature with a time scale τc, but other processes act to maintain a weak temperature gradient. There is a mass balance between radiatively driven subsidence and the large-scale convective mass flux. For a prescribed Gaussian surface temperature, the model predicts a mass flux that varies as and a convective width proportional to its reciprocal. In the boundary layer, there can be significant horizontal temperature gradients and a balance between the pressure gradient and drag is assumed. Coupling between the two layers is mediated by the vertical velocity at the top of the boundary layer. The boundary layer constrains the circulation in three ways. First, it may lengthen the relaxation time scale compared to deep convection. Second, the evaporation in the nonconvecting region constrains the horizontal moisture advection. Third, it maintains a convective boundary layer where there is a convective mass flux; this condition cannot be satisfied if τc is too small or if the drag is too large, thus showing that such values are physically impossible. These results provide testable hypotheses concerning the physics and large-scale dynamics in weather and climate models.

scholarly journals Large-scale emergence of regional changes in year-to-year temperature variability by the end of the 21st century

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Dirk Olonscheck ◽  
Andrew P. Schurer ◽  
Lucie Lücke ◽  
Gabriele C. Hegerl
Keyword(s):  
Global Warming ◽  
Large Scale ◽  
Climate Model ◽  
Climate Extremes ◽  
Temperature Variability ◽  
High Latitudes ◽  
Large Ensembles ◽  
Proxy Reconstructions ◽  
Instrumental Records ◽  
The Tropics

AbstractGlobal warming is expected to not only impact mean temperatures but also temperature variability, substantially altering climate extremes. Here we show that human-caused changes in internal year-to-year temperature variability are expected to emerge from the unforced range by the end of the 21st century across climate model initial-condition large ensembles forced with a strong global warming scenario. Different simulated changes in globally averaged regional temperature variability between models can be explained by a trade-off between strong increases in variability on tropical land and substantial decreases in high latitudes, both shown by most models. This latitudinal pattern of temperature variability change is consistent with loss of sea ice in high latitudes and changes in vegetation cover in the tropics. Instrumental records are broadly in line with this emerging pattern, but have data gaps in key regions. Paleoclimate proxy reconstructions support the simulated magnitude and distribution of temperature variability. Our findings strengthen the need for urgent mitigation to avoid unprecedented changes in temperature variability.

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