scholarly journals The Effect of Cloud Cover on the Meridional Heat Transport: Lessons from Variable Rotation Experiments

2017 ◽  
Vol 30 (18) ◽  
pp. 7465-7479 ◽  
Author(s):  
Xiaojuan Liu ◽  
David S. Battisti ◽  
Gerard H. Roe
Keyword(s):  
Heat Transport ◽  
Rotation Rate ◽  
Longwave Radiation ◽  
Eddy Diffusivity ◽  
Hadley Cell ◽  
Shortwave Radiation ◽  
Strong Increase ◽  
Meridional Heat Transport ◽  
Mixing Length Theory ◽  
Fast Rotating

Abstract The question “What determines the meridional heat transport (MHT)?” is explored by performing a series of rotation-rate experiments with an aquaplanet GCM coupled to a slab ocean. The change of meridional heat transport with rotation rate falls into two regimes: in a “slow rotating” regime (rotation rate < 1/2 modern rotation) MHT decreases with increasing rotation rate, whereas in a “fast rotating” regime (rotation rate ≥ 1/2 modern rotation) MHT is nearly invariant. The two-regime feature of MHT is primarily related to the reduction in tropical clouds and increase in tropical temperature that are associated with the narrowing and weakening of the Hadley cell with increasing rotation rate. In the slow-rotating regime, the Hadley cell contracts and weakens as rotation rate is increased; the resulting warming causes a local increase in outgoing longwave radiation (OLR), which consequently decreases MHT. In the fast-rotating regime, the Hadley cell continues to contract as rotation rate is increased, resulting in a decrease in tropical and subtropical clouds that increases the local absorbed shortwave radiation (ASR) by an amount that almost exactly compensates the local increases in OLR. In the fast-rotating regime, the model heat transport is approximately diffusive, with an effective eddy diffusivity that is consistent with eddy mixing-length theory. The effective eddy diffusivity decreases with increasing rotation rate. However, this decrease is nearly offset by a strong increase in the meridional gradient of moist static energy and hence results in a near-constancy of MHT. The results herein extend previous work on the MHT by highlighting that the spatial patterns of clouds and the factors that influence them are leading controls on MHT.

scholarly journals A Generalized Energy Balance Climate Model with Parameterized Dynamics and Diabatic Heating

2005 ◽  
Vol 18 (11) ◽  
pp. 1753-1772 ◽  
Author(s):  
Karen M. Shell ◽  
Richard C. J. Somerville
Keyword(s):  
Energy Balance ◽  
Heat Transport ◽  
Ocean Circulation ◽  
Heat Budget ◽  
Hadley Cell ◽  
Lapse Rate ◽  
Meridional Heat Transport ◽  
Temperature Changes ◽  
Global Average ◽  
Average Temperature

Abstract Energy balance models have proven useful in understanding mechanisms and feedbacks in the climate system. An original global energy balance model is presented here. The model is solved numerically for equilibrium climate states defined by zonal average temperature as a function of latitude for both a surface and an atmospheric layer. The effects of radiative, latent, and sensible heating are parameterized. The model includes a variable lapse rate and parameterizations of the major dynamical mechanisms responsible for meridional heat transport: the Hadley cell, midlatitude baroclinic eddies, and ocean circulation. The model reproduces both the mean variation of temperature with latitude and the global average heat budget within the uncertainty of observations. The utility of the model is demonstrated through examination of various climate feedbacks. One important feedback is the effect of the lapse rate on climate. When the planet warms as a result of an increase in the solar constant, the lapse rate acts as a negative feedback, effectively enhancing the longwave emission efficiency of the atmosphere. The lapse rate is also responsible for an increase in global average temperature when the meridional heat transport effectiveness is increased. The water vapor feedback enhances temperature changes, while the latent and sensible heating feedback reduces surface temperature changes.

scholarly journals Rationalizing the Spatial Distribution of Mesoscale Eddy Diffusivity in Terms of Mixing Length Theory

2014 ◽  
Vol 44 (6) ◽  
pp. 1523-1540 ◽  
Author(s):  
Michael Bates ◽  
Ross Tulloch ◽  
John Marshall ◽  
Raffaele Ferrari
Keyword(s):  
Mesoscale Eddy ◽  
Propagation Speed ◽  
Eddy Diffusivity ◽  
Mixing Length ◽  
Mean Flow ◽  
Meridional Heat Transport ◽  
Mesoscale Ocean Eddies ◽  
Mixing Rates ◽  
Lateral Mixing ◽  
Mixing Length Theory

Abstract Observations and theory suggest that lateral mixing by mesoscale ocean eddies only reaches its maximum potential at steering levels, surfaces at which the propagation speed of eddies approaches that of the mean flow. Away from steering levels, mixing is strongly suppressed because the mixing length is smaller than the eddy scale, thus reducing the mixing rates. The suppression is particularly pronounced in strong currents where mesoscale eddies are most energetic. Here, a framework for parameterizing eddy mixing is explored that attempts to capture this suppression. An expression of the surface eddy diffusivity proposed by Ferrari and Nikurashin is evaluated using observations of eddy kinetic energy, eddy scale, and eddy propagation speed. The resulting global maps of eddy diffusivity have a broad correspondence with recent estimates of diffusivity based on the rate at which tracer contours are stretched by altimetric-derived surface currents. Finally, the expression for the eddy diffusivity is extrapolated in the vertical to infer the eddy-induced meridional heat transport and the overturning streamfunction.

What Determines Meridional Heat Transport in Climate Models?

2012 ◽  
Vol 25 (11) ◽  
pp. 3832-3850 ◽  
Author(s):  
Aaron Donohoe ◽  
David S. Battisti
Keyword(s):  
Solar Radiation ◽  
Heat Transport ◽  
Outgoing Longwave Radiation ◽  
Climate Models ◽  
Longwave Radiation ◽  
Incident Radiation ◽  
Meridional Heat Transport ◽  
Surface Reflection ◽  
Global Average ◽  
Planetary Albedo

The annual mean maximum meridional heat transport (MHTMAX) differs by approximately 20% among coupled climate models. The value of MHTMAX can be expressed as the difference between the equator-to-pole contrast in absorbed solar radiation (ASR*) and outgoing longwave radiation (OLR*). As an example, in the Northern Hemisphere observations, the extratropics (defined as the region with a net radiative deficit) receive an 8.2-PW deficit of net solar radiation (ASR*) relative to the global average that is balanced by a 2.4-PW deficit of outgoing longwave radiation (OLR*) and 5.8 PW of energy import via the atmospheric and oceanic circulation (MHTMAX). The intermodel spread of MHTMAX in the Coupled Model Intercomparison Project Phase 3 (CMIP3) simulations of the preindustrial climate is primarily (R2 = 0.72) due to differences in ASR* while model differences in OLR* are uncorrelated with the MHTMAX spread. The net solar radiation (ASR*) is partitioned into contributions from (i) the equator-to-pole contrast in incident radiation acting on the global average albedo and (ii) the equator-to-pole contrast of planetary albedo, which is further subdivided into components due to atmospheric and surface reflection. In the observations, 62% of ASR* is due to the meridional distribution of incident radiation, 33% is due to atmospheric reflection, and 5% is due to surface reflection. The intermodel spread in ASR* is due to model differences in the equator-to-pole gradient in planetary albedo, which are primarily a consequence of atmospheric reflection differences (92% of the spread), and is uncorrelated with differences in surface reflection. As a consequence, the spread in MHTMAX in climate models is primarily due to the spread in cloud reflection properties.

scholarly journals Dynamical and Thermodynamical Impacts of High- and Low-Frequency Atmospheric Eddies on the Initial Melt of Arctic Sea Ice

2017 ◽  
Vol 30 (3) ◽  
pp. 865-883 ◽  
Author(s):  
Bradley M. Hegyi ◽  
Yi Deng
Keyword(s):  
Sea Ice ◽  
Heat Transport ◽  
High Frequency ◽  
Low Frequency ◽  
Longwave Radiation ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Positive Anomaly ◽  
Meridional Heat Transport ◽  
Arctic Sea

Abstract The role of high-frequency and low-frequency eddies in the melt onset of Arctic sea ice is investigated through an examination of eddy effects on lower-tropospheric (1000–500 hPa) meridional heat transport into the Arctic and local surface downwelling shortwave and longwave radiation. Total and eddy components of the meridional heat transport into the Arctic from 1979 to 2012 are calculated from reanalysis data, and surface radiation data are acquired from the NASA Clouds and the Earth’s Radiant Energy System (CERES) project dataset. There is a significant positive correlation between the mean initial melt date and the September sea ice minimum extent, with each quantity characterized by a negative trend. Spatially, the earlier mean melt onset date is primarily found in a region bounded by 90°E and 130°W. The decline in this region is steplike and not associated with an increase in meridional heat transport but with an earlier appearance of above-freezing temperatures in the troposphere. In most years, discrete short-duration episodes of melt onset over a large area occur. In an investigation of two of these melt episodes, a positive total meridional heat transport is associated with the peak melt, with the product of high-frequency eddy wind and mean temperature fields being the most important contributor. Additionally, there is a key positive anomaly in surface downwelling longwave radiation immediately preceding the peak melt that is associated with increased cloud cover and precipitable water. These results suggest the importance of carefully considering and properly representing atmospheric eddies when modeling the melt onset of Arctic sea ice.

Radiative and Dynamic Controls on Atmospheric Heat Transport over Different Planetary Rotation Rates

2021 ◽  
Vol 34 (9) ◽  
pp. 3543-3554
Author(s):  
Tyler Cox ◽  
Kyle C. Armour ◽  
Gerard H. Roe ◽  
Aaron Donohoe ◽  
Dargan M. W. Frierson
Keyword(s):  
Heat Transport ◽  
Rotation Rate ◽  
Hadley Cell ◽  
Slow Rotation ◽  
Rotation Rates ◽  
Planetary Rotation ◽  
Atmospheric Heat Transport ◽  
Mean Meridional Circulation ◽  
Radiative Temperature ◽  
Atmospheric Heat

AbstractAtmospheric heat transport is an important piece of our climate system, yet we lack a complete theory for its magnitude or changes. Atmospheric dynamics and radiation play different roles in controlling the total atmospheric heat transport (AHT) and its partitioning into components associated with eddies and mean meridional circulations. This work focuses on two specific controls: a radiative one, namely atmospheric radiative temperature tendencies, and a dynamic one, the planetary rotation rate. We use an idealized gray radiation model to employ a novel framework to lock the radiative temperature tendency and total AHT to climatological values, even while the rotation rate is varied. This setup allows for a systematic study of the effects of radiative tendency and rotation rate on AHT. We find that rotation rate controls the latitudinal extent of the Hadley cell and the heat transport efficiency of eddies. Both the rotation rate and radiative tendency influence the strength of the Hadley cell and the strength of equator–pole energy differences that are important for AHT by eddies. These two controls do not always operate independently and can reinforce or dampen each other. In addition, we examine how individual AHT components, which vary with latitude, sum to a total AHT that varies smoothly with latitude. At slow rotation rates the mean meridional circulation is most important in ensuring total AHT varies smoothly with latitude, while eddies are most important at rotation rates similar to, and faster than, those of Earth.

scholarly journals Meteorological controls on snow and ice ablation for two contrasting months on Glacier de Saint-Sorlin, France

2009 ◽  
Vol 50 (50) ◽  
pp. 66-72 ◽  
Author(s):  
D. Six ◽  
P. Wagnon ◽  
J.E. Sicart ◽  
C. Vincent
Keyword(s):  
Energy Balance ◽  
Mass Balance ◽  
Turbulent Flux ◽  
Longwave Radiation ◽  
Sharp Decrease ◽  
Shortwave Radiation ◽  
Strong Increase ◽  
Ice Melting ◽  
Measured Mass ◽  
Good Agreement

AbstractThe influence of meteorological variables on snow/ice melting has been analyzed for two very contrasting months, in summer 2006, on Glacier de Saint-Sorlin, French Alps. July 2006 was the warmest July since 1950, and August 2006 was the coldest August since 1979. The total energy available for melting was just over half as much in August as in July, due to a sharp decrease in net shortwave radiation and in turbulent flux. This decrease of net shortwave radiation was mainly controlled by a strong increase in albedo responsible for an increase of reflected shortwave radiation, as well as by a reduction in incident shortwave radiation. During the two months, net longwave radiation remained almost unchanged. The mass balance computed from energy-balance modelling or with a degree-day approach was in good agreement with measured mass balance. Differences were attributed to space and time surface aspect variations which mainly controlled the observed mass balance.

scholarly journals An Evaluation of Surface Atmospheric Changes over the Arctic Ocean for 2000–09 Using Recent Reanalyses

2015 ◽  
Vol 19 (2) ◽  
pp. 1-18 ◽  
Author(s):  
Ayan H. Chaudhuri ◽  
Rui M. Ponte
Keyword(s):  
Arctic Ocean ◽  
Extreme Event ◽  
Longwave Radiation ◽  
Remotely Sensed ◽  
Surface Radiation ◽  
Shortwave Radiation ◽  
The Arctic ◽  
Near Surface ◽  
The Arctic Ocean ◽  
Ice Retreat

Abstract The authors examine five recent reanalysis products [NCEP Climate Forecast System Reanalysis (CFSR), Modern-Era Retrospective Analysis for Research and Applications (MERRA), Japanese 25-year Reanalysis Project (JRA-25), Interim ECMWF Re-Analysis (ERA-Interim), and Arctic System Reanalysis (ASR)] for 1) trends in near-surface radiation fluxes, air temperature, and humidity, which are important indicators of changes within the Arctic Ocean and also influence sea ice and ocean conditions, and 2) fidelity of these atmospheric fields and effects for an extreme event: namely, the 2007 ice retreat. An analysis of trends over the Arctic for the past decade (2000–09) shows that reanalysis solutions have large spreads, particularly for downwelling shortwave radiation. In many cases, the differences in significant trends between the five reanalysis products are comparable to the estimated trend within a particular product. These discrepancies make it difficult to establish a consensus on likely changes occurring in the Arctic solely based on results from reanalyses fields. Regarding the 2007 ice retreat event, comparisons with remotely sensed estimates of downwelling radiation observations against these reanalysis products present an ambiguity. Remotely sensed observations from a study cited herewith suggest a large increase in downwelling summertime shortwave radiation and decrease in downwelling summertime longwave radiation from 2006 and 2007. On the contrary, the reanalysis products show only small gains in summertime shortwave radiation, if any; however, all the products show increases in downwelling longwave radiation. Thus, agreement within reanalysis fields needs to be further checked against observations to assess possible biases common to all products.

Drivers of (non-)linear Eocene surface warming in the DeepMIP ensemble

2021 ◽  
Author(s):  
Sebastian Steinig ◽  
Jiang Zhu ◽  
Ran Feng ◽  
Keyword(s):  
Temperature Gradient ◽  
Heat Transport ◽  
Climate Sensitivity ◽  
Radiative Forcing ◽  
Large Scale ◽  
Surface Albedo ◽  
Early Eocene ◽  
Meridional Heat Transport ◽  
Surface Warming ◽  
Global Mean

<p>The early Eocene greenhouse represents the warmest interval of the Cenozoic and therefore provides a unique opportunity to understand how the climate system operates under elevated atmospheric CO<sub>2</sub> levels similar to those projected for the end of the 21st century. Early Eocene geological records indicate a large increase in global mean surface temperatures compared to present day (by ~14°C) and a greatly reduced meridional temperature gradient (by ~30% in SST). However, reproducing these large-scale climate features at reasonable CO<sub>2</sub> levels still poses a challenge for current climate models. Recent modelling studies indicate an important role for shortwave (SW) cloud feedbacks to drive increases in climate sensitivity with global warming, which helps to close the gap between simulated and reconstructed Eocene global warmth and temperature gradient. Nevertheless, the presence of such state-dependent feedbacks and their relative strengths in other models remain unclear.</p><p>In this study, we perform a systematic investigation of the simulated surface warming and the underlying mechanisms in the recently published DeepMIP ensemble. The DeepMIP early Eocene simulations use identical paleogeographic boundary conditions and include six models with suitable output: CESM1.2_CAM5, GFDL_CM2.1, HadCM3B_M2.1aN, IPSLCM5A2, MIROC4m and NorESM1_F. We advance previous energy balance analysis by applying the approximate partial radiative perturbation (APRP) technique to quantify the individual contributions of surface albedo, cloud and non-cloud atmospheric changes to the simulated Eocene top-of-the-atmosphere SW flux anomalies. We further compare the strength of these planetary albedo feedbacks to changes in the longwave atmospheric emissivity and meridional heat transport in the warm Eocene climate. Particular focus lies in the sensitivity of the feedback strengths to increasing global mean temperatures in experiments at a range of atmospheric CO<sub>2</sub> concentrations between x1 to x9 preindustrial levels.</p><p>Preliminary results indicate that all models that provide data for at least 3 different CO<sub>2</sub> levels show an increase of the equilibrium climate sensitivity at higher global mean temperatures. This is associated with an increase of the overall strength of the positive SW cloud feedback with warming in those models. This nonlinear behavior seems to be related to both a reduction and optical thinning of low-level clouds, albeit with intermodel differences in the relative importance of the two mechanisms. We further show that our new APRP results can differ significantly from previous estimates based on cloud radiative forcing alone, especially in high-latitude areas with large surface albedo changes. We also find large intermodel variability and state-dependence in meridional heat transport modulated by changes in the atmospheric latent heat transport. Ongoing work focuses on the spatial patterns of the climate feedbacks and the implications for the simulated meridional temperature gradients.</p>

scholarly journals Oceanic Overturning and Heat Transport: The Role of Background Diffusivity

2019 ◽  
Vol 32 (3) ◽  
pp. 701-716 ◽  
Author(s):  
Magnus Hieronymus ◽  
Jonas Nycander ◽  
Johan Nilsson ◽  
Kristofer Döös ◽  
Robert Hallberg
Keyword(s):  
Heat Transport ◽  
Large Scale ◽  
Energy Transport ◽  
Climate Model ◽  
Potential Temperature ◽  
Meridional Heat Transport ◽  
Sea Ice Extent ◽  
Antarctic Sea Ice ◽  
Meridional Overturning

The role of oceanic background diapycnal diffusion for the equilibrium climate state is investigated in the global coupled climate model CM2G. Special emphasis is put on the oceanic meridional overturning and heat transport. Six runs with the model, differing only by their value of the background diffusivity, are run to steady state and the statistically steady integrations are compared. The diffusivity changes have large-scale impacts on many aspects of the climate system. Two examples are the volume-mean potential temperature, which increases by 3.6°C between the least and most diffusive runs, and the Antarctic sea ice extent, which decreases rapidly as the diffusivity increases. The overturning scaling with diffusivity is found to agree rather well with classical theoretical results for the upper but not for the lower cell. An alternative empirical scaling with the mixing energy is found to give good results for both cells. The oceanic meridional heat transport increases strongly with the diffusivity, an increase that can only partly be explained by increases in the meridional overturning. The increasing poleward oceanic heat transport is accompanied by a decrease in its atmospheric counterpart, which keeps the increase in the planetary energy transport small compared to that in the ocean.

scholarly journals Simulation of Thermodynamic Features of a Thunderstorm Event over Dhaka using WRF-ARW Model

2018 ◽  
Vol 37 ◽  
pp. 131-145
Author(s):  
Md Mijanur Rahman ◽  
Md Abdus Samad ◽  
SM Quamrul Hassan
Keyword(s):  
Convective Available Potential Energy ◽  
Model Performance ◽  
Vertical Wind Shear ◽  
Longwave Radiation ◽  
Final Analysis ◽  
Horizontal Resolution ◽  
Cumulus Parameterization ◽  
Shortwave Radiation ◽  
Radiative Transfer Model ◽  
Transfer Model

An attempt has been made to simulate the thermodynamic features of the thunderstorm (TS) event over Dhaka (23.81°N, 90.41°E) occurred from 1300 UTC to 1320 UTC of 4 April 2015 using Advanced Research dynamics solver of Weather Research and Forecasting model (WRF-ARW). The model was run to conduct a simulation for 48 hours on a single domain of 5 km horizontal resolution utilizing six hourly Global Final Analysis (FNL) datasets from 0600 UTC of 3 April 2015 to 0600 UTC of 5 April 2015 as initial and lateral boundary conditions. Kessler schemes for microphysics, Yonsei University (YSU) scheme for planetary boundary layer (PBL) parametrization, Revised MM5 scheme for surface layer physics, Rapid Radiative Transfer Model (RRTM) for longwave radiation, Dudhia scheme for shortwave radiation and Kain–Fritsch (KF) scheme for cumulus parameterization were used. Hourly outputs produced by the model have been analyzed numerically and graphically using Grid Analysis and Display System (GrADS). Deep analyses were carried out by examining several thermodynamic parameters such as mean sea level pressure (MSLP), wind pattern, vertical wind shear, vorticity, temperature, convective available potential energy (CAPE), relative humidity (RH) and rainfall. To validate the model performance, simulated values of MSLP, maximum and minimum temperature and RH were compared with observational data obtained from Bangladesh Meteorological Department (BMD). Rainfall values were compared with that of BMD and Tropical Rainfall Measuring Mission (TRMM) of National Aeronautics and Space Administration (NASA). Based on the comparisons and validations, the present study advocates that the model captured the TS event reasonably well.GANIT J. Bangladesh Math. Soc.Vol. 37 (2017) 131-145

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