Diurnal cycle of tropical precipitation in a general circulation model

2004 ◽  
Vol 109 (D17) ◽  
Author(s):  
J. Craig Collier
Keyword(s):  
General Circulation Model ◽  
Diurnal Cycle ◽  
General Circulation ◽  
Circulation Model ◽  
Tropical Precipitation

Regional Tropical Precipitation Change Mechanisms in ECHAM4/OPYC3 under Global Warming*

2006 ◽  
Vol 19 (17) ◽  
pp. 4207-4223 ◽  
Author(s):  
Chia Chou ◽  
J. David Neelin ◽  
Jien-Yi Tu ◽  
Cheng-Ta Chen
Keyword(s):  
Global Warming ◽  
Greenhouse Gases ◽  
General Circulation Model ◽  
General Circulation ◽  
Vertical Motion ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Additional Contribution ◽  
Tropical Precipitation ◽  
Precipitation Anomalies

Abstract Mechanisms of global warming impacts on regional tropical precipitation are examined in a coupled atmosphere–ocean general circulation model (ECHAM4/OPYC3). The pattern of the regional tropical precipitation changes, once established, tends to persist, growing in magnitude as greenhouse gases increase. The sulfate aerosol induces regional tropical precipitation anomalies similar to the greenhouse gases but with opposite sign, thus reducing the early signal. Evidence for two main mechanisms, the upped-ante and the anomalous gross moist stability (M′) mechanisms (previously proposed in an intermediate complexity model), is found in this more comprehensive coupled general circulation model. Preferential moisture increase occurs in convection zones. The upped-ante mechanism signature of dry advection from nonconvective regions is found in tropical drought regions on the margins of convection zones. Here advection in both the atmospheric boundary layer and lower free troposphere are found to be important, with an additional contribution from horizontal temperature transport in some locations. The signature of the M′ mechanism—moisture convergence due to increased moisture in regions of large mean vertical motion—enhances precipitation within strong convective regions. Ocean dynamical feedbacks can be assessed by net surface flux, the main example being the El Niño–like shift of the equatorial Pacific convection zone. Cloud–radiative feedbacks are found to oppose precipitation anomalies over ocean regions.

scholarly journals Superparameterised cloud effects in the EMAC general circulation model (v2.50) – influences of model configuration

2020 ◽  
Vol 13 (6) ◽  
pp. 2671-2694
Author(s):  
Harald Rybka ◽  
Holger Tost
Keyword(s):  
General Circulation Model ◽  
Diurnal Cycle ◽  
General Circulation ◽  
Cloud Cover ◽  
Large Scale ◽  
Current Model ◽  
Sensible Heat Flux ◽  
Circulation Model ◽  
Cloud Amount ◽  
Model Configuration

Abstract. A new module has been implemented in the fifth generation of the ECMWF/Hamburg (ECHAM5)/Modular Earth Submodel System (MESSy) Atmospheric Chemistry (EMAC) model that simulates cloud-related processes on a much smaller grid. This so-called superparameterisation acts as a replacement for the convection parameterisation and large-scale cloud scheme. The concept of embedding a cloud-resolving model (CRM) inside of each grid box of a general circulation model leads to an explicit representation of cloud dynamics. The new model component is evaluated against observations and the conventional usage of EMAC using a convection parameterisation. In particular, effects of applying different configurations of the superparameterisation are analysed in a systematical way. Consequences of changing the CRM's orientation, cell size and number of cells range from regional differences in cloud amount up to global impacts on precipitation distribution and its variability. For some edge case setups, the analysed climate state of superparameterised simulations even deteriorates from the mean observed energy budget. In the current model configuration, different climate regimes can be formed that are mainly driven by some of the parameters of the CRM. Presently, the simulated total cloud cover is at the lower edge of the CMIP5 model ensemble. However, certain “tuning” of the current model configuration could improve the slightly underestimated cloud cover, which will result in a shift of the simulated climate. The simulation results show that especially tropical precipitation is better represented with the superparameterisation in the EMAC model configuration. Furthermore, the diurnal cycle of precipitation is heavily affected by the choice of the CRM parameters. However, despite an improvement of the representation of the continental diurnal cycle in some configurations, other parameter choices result in a deterioration compared to the reference simulation using a conventional convection parameterisation. The ability of the superparameterisation to represent latent and sensible heat flux climatology is independent of the chosen CRM setup. Evaluation of in-atmosphere cloud amounts depending on the chosen CRM setup shows that cloud development can significantly be influenced on the large scale using a too-small CRM domain size. Therefore, a careful selection of the CRM setup is recommended using 32 or more CRM cells to compensate for computational expenses.

scholarly journals Simulated radiative forcing from contrails and contrail cirrus

2013 ◽  
Vol 13 (4) ◽  
pp. 10939-10959 ◽  
Author(s):  
C.-C. Chen ◽  
A. Gettelman
Keyword(s):  
General Circulation Model ◽  
Diurnal Cycle ◽  
Radiative Forcing ◽  
General Circulation ◽  
Circulation Model ◽  
Climate Impact ◽  
Hydrologic Cycle ◽  
Regional Effect ◽  
Emissions Inventory ◽  
Aviation Emissions

Abstract. A comprehensive general circulation model including ice supersaturation is used to estimate the climate impact of aviation induced contrails. The model uses a realistic aviation emissions inventory for 2006 to initiate contrails, and allows them to evolve consistently with the model hydrologic cycle. The radiative forcing from linear contrails is very sensitive to the diurnal cycle of flights. For linear contrails, including the diurnal cycle of flights reduces the estimated global radiative forcing by 55%, and for contrails cirrus estimates, the global radiative forcing is reduced by 25%. Estimated global radiative forcing from linear contrails is 0.0029±0.00125 W m−2. The instantaneous radiative forcing for contrails is found to exhibit a strong diurnal cycle. The integrated effect of contrail cirrus is much less sensitive to the diurnal cycle of flights. The estimated global radiative forcing from contrail cirrus is 0.012±0.01 W m−2. Over regions with the highest air traffic, the regional effect can be as large as 1 W m−2.

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