scholarly journals Importance of Circulation Changes to Atlantic Heat Storage Rates on Seasonal and Interannual Time Scales

2012 ◽  
Vol 25 (1) ◽  
pp. 350-362 ◽  
Author(s):  
Christopher G. Piecuch ◽  
Rui M. Ponte
Keyword(s):  
Heat Transport ◽  
Time Scales ◽  
General Circulation ◽  
Heat Storage ◽  
Circulation Model ◽  
Surface Heat ◽  
Heat Fluxes ◽  
Meridional Heat Transport ◽  
Tropical Regions ◽  
Circulation Changes

Abstract Ocean heat budgets and transports are diagnosed to elucidate the importance of general circulation changes to Atlantic Ocean heat storage rates. The focus is on low- and midlatitude regions and on seasonal and interannual time scales. An estimate of the ocean state over 1993–2004, produced by a coarse-resolution general circulation model fit to observations via the method of Lagrange multipliers, is used. Meridional heat transports are first decomposed into contributions from time-mean and time-variable velocity and temperature and second from zonally symmetric baroclinic (overturning, including Ekman) and zonally asymmetric (gyre and other spatially correlated) circulations. Heat storage rates are then ascribed to ocean–atmosphere heat exchanges, diffusive mixing, and advective processes related to the various components of the meridional heat transport. Results show that seasonal heat storage changes generally represent a local response to surface heat inputs, but seasonal advective changes are also important near the equator. Interannual heat storage rate anomalies are mostly due to advection in tropical regions, whereas both surface heat fluxes and advection contribute at higher latitudes. Low-latitude advection can be primarily attributed to zonally symmetric baroclinic circulations, but temperature variations and zonally asymmetric flows can contribute elsewhere. A relationship between interannual heat storage rates in the equatorial Atlantic’s top 100 m and meridional heat transport associated with the zonally symmetric baroclinic flow is observed; however, due in part to the role of shallow advective processes at these latitudes, any direct relationship between sea surface temperature variability and heat transport changes associated with intermediate or deep meridional overturning circulations is not clear.

scholarly journals Diagnosing Natural Variability of North Atlantic Water Masses in HadCM3

2005 ◽  
Vol 18 (12) ◽  
pp. 1925-1941 ◽  
Author(s):  
Keith Haines ◽  
Chris Old
Keyword(s):  
Mixed Layer ◽  
General Circulation ◽  
Circulation Model ◽  
Surface Heat ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Mode Water ◽  
Surface Heat Fluxes ◽  
Mode Waters ◽  
Winter Mixed Layer

Abstract A study of thermally driven water mass transformations over 100 yr in the ocean component of the Third Hadley Centre Coupled Ocean–Atmosphere General Circulation Model (HadCM3) is presented. The processes of surface-forced transformations, subduction and mixing, both above and below the winter mixed layer base, are quantified. Subtropical Mode Waters are formed by surface heat fluxes and subducted at more or less the same rate. However, Labrador Seawater and Nordic Seawater classes (the other main subduction classes) are primarily formed by mixing within the mixed layer with very little formation directly from surface heat fluxes. The Subpolar Mode Water classes are dominated by net obduction of water back into the mixed layer from below. Subtropical Mode Water (18°C) variability shows a cycle of formation by surface fluxes, subduction ∼2 yr later, followed by mixing with warmer waters below the winter mixed layer base during the next 3 yr, and finally obduction back into the mixed layer at 21°C, ∼5 yr after the original formation. Surface transformation of Subpolar Mode Waters, ∼12°C, are led by surface transformations of warmer waters by up to 5 yr as water is transferred from the subtropical gyre. They are also led by obduction variability from below the mixed layer, by ∼2 yr. The variability of obduction in Subpolar Mode Waters also appears to be preceded, by 3–5 yr, by variability in subduction of Labrador Sea Waters at ∼6°C. This supports a mechanism in which southward-propagating Labrador seawater anomalies below the subpolar gyre can influence the upper water circulation and obduction into the mixed layer.

scholarly journals Oceanic dominance of interannual subtropical North Atlantic heat content variability

2013 ◽  
Vol 10 (1) ◽  
pp. 27-53 ◽  
Author(s):  
M. Sonnewald ◽  
J. J.-M. Hirschi ◽  
R. Marsh
Keyword(s):  
Heat Transport ◽  
North Atlantic ◽  
General Circulation ◽  
Low Frequency ◽  
Heat Content ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Heat Fluxes ◽  
Ocean Heat Content ◽  
Box Model

Abstract. Ocean heat content varies on a range of timescales. Traditionally the atmosphere is seen to dominate the oceanic heat content variability. However, this variability can be driven either by oceanic or atmospheric heat fluxes. To diagnose the relative contributions and respective timescales, this study uses a box model forced with output from an ocean general circulation model (OGCM) to investigate the heat content variability of the upper 800 m of the subtropical North Atlantic from 26° N to 36° N. The ocean and air-sea heat flux data needed to force the box model is taken from a 19 yr (1988 to 2006) simulation performed with the 1/12° version of the OCCAM OGCM. The box model heat content is compared to the corresponding heat content in OCCAM for verification. The main goal of the study is to identify to what extent the seasonal to interannual ocean heat content variability is of atmospheric or oceanic origin. To this end, the box model is subjected to a range of scenarios forced either with the full (detrended) ocean and air-sea fluxes, or their deseasoned counterparts. Results show that in all cases, the seasonal variability is dominated by the seasonal component of the air-sea fluxes, which produce a seasonal range in mean temperature of the upper 800 m of ~ 0.42 °C. However, on longer timescales oceanic heat transport dominates, with changes of up to ~ 0.30 °C over 4 yr. The technique is subsequently applied to observational data. For the ocean heat fluxes, we use data from the RAPID program at 26° N from April 2004 to January 2011. At 36° N heat transport is inferred using a linear regression model based on the oceanic low-frequency transport in OCCAM. The air-sea flux from OCCAM is used for the period 2004 to 2006 when the RAPID timeseries and the OCCAM simulation overlap, and a climatology is used for the air-sea flux from 2006 onwards. The results confirm that on longer (> 2 yr) timescales the ocean dominates the ocean heat content variability, which is further verified using data from the ARGO project. This work illustrates that oceanic divergence significantly impacts the ocean heat content variability on timescales relevant for applications such as seasonal hurricane forecasts.

Bjerknes Compensation at High Northern Latitudes: The Ocean Forcing the Atmosphere

2007 ◽  
Vol 20 (24) ◽  
pp. 6023-6032 ◽  
Author(s):  
E. van der Swaluw ◽  
S. S. Drijfhout ◽  
W. Hazeleger
Keyword(s):  
Heat Transport ◽  
Time Scales ◽  
General Circulation ◽  
Circulation Model ◽  
Open Water ◽  
Meridional Overturning Circulation ◽  
Atmospheric Response ◽  
Using Data ◽  
Hadley Centre ◽  
Sst Anomalies

Abstract The mechanisms for Bjerknes compensation of heat transport variations through the atmosphere and ocean on decadal time scales are investigated, using data output from a preindustrial control run of the Third Hadley Centre Coupled Ocean–Atmosphere General Circulation Model (HadCM3). It has recently been shown that Bjerknes compensation occurs on decadal time scales in a long preindustrial control run of HadCM3. This result is elaborated on by performing lead/lag correlations of the atmospheric and oceanic heat transports. By using statistical analysis, Bjerknes compensation is observed on decadal time scales at latitudes between 50° and 80°N. A maximum compensation rate of ∼55% occurs at 70°N. At this latitude, the correlation rate peaks when the ocean leads the atmosphere by one year. The mechanisms by which Bjerknes compensation occurs at this latitude are investigated. Anomalies in oceanic heat transport appear to be associated with variations in the strength of the Atlantic meridional overturning circulation (MOC). The associated sea surface temperature (SST) anomalies are in general too weak to assert a significant impact on the atmosphere. At 70°N, however, such SST anomalies are a prelude to the transition from sea ice coverage to open water after which the associated changes in heat exchange with the atmosphere are strong enough to force an atmospheric response. Because of the presence of a strong MOC component in the Atlantic Ocean, this interaction is confined to the region where the northeast Atlantic and Arctic Oceans connect. The atmospheric response to increased (decreased) heating from below is a decreased (increased) poleward temperature gradient, leading to a decreased (increased) heat transport by baroclinic eddies. The anomalous thermal low that is set up by heating from the ocean is associated with anomalous advection of cold air from the Greenland landmass.

scholarly journals Albedo and heat transport in 3-D model simulations of the early Archean climate

2013 ◽  
Vol 9 (4) ◽  
pp. 1841-1862 ◽  
Author(s):  
H. Kienert ◽  
G. Feulner ◽  
V. Petoukhov
Keyword(s):  
Heat Transport ◽  
General Circulation ◽  
Climate Model ◽  
Stable State ◽  
Circulation Model ◽  
Ocean Surface ◽  
Meridional Heat Transport ◽  
Model Simulations ◽  
D Model ◽  
Archean Climate

Abstract. At the beginning of the Archean eon (ca. 3.8 billion years ago), the Earth's climate state was significantly different from today due to the lower solar luminosity, smaller continental fraction, higher rotation rate and, presumably, significantly larger greenhouse gas concentrations. All these aspects play a role in solutions to the "faint young Sun paradox" which must explain why the ocean surface was not fully frozen at that time. Here, we present 3-D model simulations of climate states that are consistent with early Archean boundary conditions and have different CO2 concentrations, aiming at an understanding of the fundamental characteristics of the early Archean climate system. In order to do so, we have appropriately modified an intermediate complexity climate model that couples a statistical-dynamical atmosphere model (involving parameterizations of the dynamics) to an ocean general circulation model and a thermodynamic-dynamic sea-ice model. We focus on three states: one of them is ice-free, one has the same mean surface air temperature of 288 K as today's Earth and the third one is the coldest stable state in which there is still an area with liquid surface water (i.e. the critical state at the transition to a "snowball Earth"). We find a reduction in meridional heat transport compared to today, which leads to a steeper latitudinal temperature profile and has atmospheric as well as oceanic contributions. Ocean surface velocities are largely zonal, and the strength of the atmospheric meridional circulation is significantly reduced in all three states. These aspects contribute to the observed relation between global mean temperature and albedo, which we suggest as a parameterization of the ice-albedo feedback for 1-D model simulations of the early Archean and thus the faint young Sun problem.

scholarly journals The Role of High-Latitude Waves in the Intraseasonal to Seasonal Variability of Tropical Upwelling in the Brewer–Dobson Circulation

2013 ◽  
Vol 70 (6) ◽  
pp. 1631-1648 ◽  
Author(s):  
Rei Ueyama ◽  
Edwin P. Gerber ◽  
John M. Wallace ◽  
Dargan M. W. Frierson
Keyword(s):  
Time Scales ◽  
General Circulation ◽  
Winter Season ◽  
Circulation Model ◽  
Heat Fluxes ◽  
Planetary Waves ◽  
Boreal Winter ◽  
High Latitudes ◽  
Radiative Relaxation ◽  
Stratospheric Temperature

Abstract The forcing of tropical upwelling in the Brewer–Dobson circulation (BDC) on intraseasonal to seasonal time scales is investigated in integrations of an idealized general circulation model, ECMWF Interim Re-Analysis, and lower-stratospheric temperature measurements from the (Advanced) Microwave Sounding Unit, with a focus on the extended boreal winter season. Enhanced poleward eddy heat fluxes in the high latitudes (45°–90°N) at the 100-hPa level are associated with anomalous tropical cooling and anomalous warming on the poleward side of the polar night jet at the 70-hPa level and above. In both the model and the observations, planetary waves entering the stratosphere at high latitudes propagate equatorward to the subtropics and tropics at levels above 70 hPa over an approximately 10-day period, exerting a force at sufficiently low latitudes to modulate the tropical upwelling in the upper branch of the BDC, even on time scales longer than the radiative relaxation time scale of the lower stratosphere. To the extent that they force the BDC via downward as opposed to sideways control, planetary waves originating in high latitudes contribute to the seasonally varying climatological mean and the interannual variability of tropical upwelling at the 70-hPa level and above. Their influence upon the strength of the tropical upwelling, however, diminishes rapidly with depth below 70 hPa. In particular, tropical upwelling at the cold-point tropopause, near 100 hPa, appears to be modulated by variations in the strength of the lower branch of the BDC.

scholarly journals Thermodynamic feedback processes in a single-column sea-ice-ocean model

1997 ◽  
Vol 25 ◽  
pp. 327-332 ◽  
Author(s):  
Marika M. Holland ◽  
Julie L. Schramm ◽  
Judith A. Curry
Keyword(s):  
Heat Flux ◽  
Sea Ice ◽  
Surface Heat Flux ◽  
General Circulation ◽  
Accurate Determination ◽  
Circulation Model ◽  
Surface Heat ◽  
Physical Processes ◽  
Feedback Mechanisms ◽  
Albedo Feedback

Due to large uncertainties in many of the parameters used to model sea ice, it is possible that models with significantly different physical processes can be tuned to obtain realistic present-day simulations. However, in studies of climate change, it is the response of the model it various perturbations that is important, in studies response can be significantly different in sea-ice models that include or exclude various physical feedback mechanisms. Because simplifications in sea-ice physics are necessary for general circulation model experiments, it is important to assess which physical processes are essential for the accurate determination of the sensitivity of the ice pack to climate perturbations. We have attempted to address these issues using a new coupled ice-thickness distribution ocean mixed-layer model. The sensitivity of the model to surface heat-flux perturbations is examined and the importance of the ice ocean and ice-albedo feedback mechanisms in determining this sensitivity is analyzed. We find that the ice ocean and ice-albedo feedback processes are not mutually exclusive, and that they both significantly alter the model response to surface heat flux perturbations.

scholarly journals A Tropospheric Emission Spectrometer HDO/H<sub>2</sub>O retrieval simulator for climate models

2012 ◽  
Vol 12 (6) ◽  
pp. 13827-13880
Author(s):  
R. D. Field ◽  
C. Risi ◽  
G. A. Schmidt ◽  
J. Worden ◽  
A. Voulgarakis ◽  
...  
Keyword(s):  
Time Scales ◽  
General Circulation ◽  
Climate Models ◽  
Circulation Model ◽  
Satellite Measurement ◽  
Climate Simulations ◽  
Accurate Comparison ◽  
Free Running ◽  
The Tropics ◽  
Short Time

Abstract. Retrievals of the isotopic composition of water vapor from the Aura Tropospheric Emission Spectrometer (TES) have unique value in constraining moist processes in climate models. Accurate comparison between simulated and retrieved values requires that model profiles that would be poorly retrieved are excluded, and that an instrument operator be applied to the remaining profiles. Typically, this is done by sampling model output at satellite measurement points and using the quality flags and averaging kernels from individual retrievals at specific places and times. This approach is not reliable when the modeled meteorological conditions influencing retrieval sensitivity are different from those observed by the instrument at short time scales, which will be the case for free-running climate simulations. In this study, we describe an alternative, "categorical" approach to applying the instrument operator, implemented within the NASA GISS ModelE general circulation model. Retrieval quality and averaging kernel structure are predicted empirically from model conditions, rather than obtained from collocated satellite observations. This approach can be used for arbitrary model configurations, and requires no agreement between satellite-retrieved and modeled meteorology at short time scales. To test this approach, nudged simulations were conducted using both the retrieval-based and categorical operators. Cloud cover, surface temperature and free-tropospheric moisture content were the most important predictors of retrieval quality and averaging kernel structure. There was good agreement between the δD fields after applying the retrieval-based and more detailed categorical operators, with increases of up to 30‰ over the ocean and decreases of up to 40‰ over land relative to the raw model fields. The categorical operator performed better over the ocean than over land, and requires further refinement for use outside of the tropics. After applying the TES operator, ModelE had δD biases of −8‰ over ocean and −34‰ over land compared to TES δD, which were less than the biases using raw modeled δD fields.

First results from coupling the Parallel Ice Sheet Model with the Modular Ocean Model via an Antarctic ice-shelf cavity module

2021 ◽  
Author(s):  
Moritz Kreuzer ◽  
Ronja Reese ◽  
Willem Huiskamp ◽  
Stefan Petri ◽  
Torsten Albrecht ◽  
...  
Keyword(s):  
Time Scales ◽  
General Circulation ◽  
Ice Sheet ◽  
Circulation Model ◽  
Ocean Model ◽  
Global Ocean ◽  
Ice Shelf ◽  
Antarctic Ice Sheet ◽  
First Results ◽  
The Antarctic

&lt;p&gt;The past and future evolution of the Antarctic Ice Sheet is largely controlled by interactions between the ocean and floating ice shelves. To investigate these interactions, coupled ocean and ice sheet model configurations are required. Previous modelling studies have mostly relied on high resolution configurations, limiting these studies to individual glaciers or regions over short time scales of decades to a few centuries. To study global and long term interactions, we developed a framework to couple the dynamic ice sheet model PISM with the global ocean general circulation model MOM5 via the ice-shelf cavity module PICO. Since ice-shelf cavities are not resolved by MOM5, but parameterized with the box model PICO, the framework allows the ice sheet and ocean model to be run at resolution of 16&amp;#8201;km and 3 degrees, respectively. We present first results from our coupled setup and discuss stability, feedbacks, and interactions of the Antarctic Ice Sheet and the global ocean system on millennial time scales.&lt;/p&gt;

scholarly journals Essential Ingredients to the Dynamics of Westerly Wind Bursts

2019 ◽  
Vol 32 (17) ◽  
pp. 5549-5565 ◽  
Author(s):  
Minmin Fu ◽  
Eli Tziperman
Keyword(s):  
General Circulation ◽  
Circulation Model ◽  
Basic Mechanism ◽  
Surface Heat ◽  
Convective Heating ◽  
Short Time Scale ◽  
Westerly Wind ◽  
Atmospheric Phenomena ◽  
Wind Bursts ◽  
Westerly Wind Bursts

Abstract Westerly wind bursts (WWBs) are brief, anomalously westerly winds in the tropical Pacific that play a role in the dynamics of ENSO through their forcing of ocean Kelvin waves. They have been associated with atmospheric phenomena such as tropical cyclones, the MJO, and convectively coupled Rossby waves, yet their basic mechanism is not yet well understood. We study WWBs using an aquaplanet general circulation model, and find that eastward-propagating convective heating plays a key role in the generation of model WWBs, consistent with previous studies. Furthermore, wind-induced surface heat exchange (WISHE) acts on a short time scale of about two days to dramatically amplify the model WWB winds near the peak of the event. On the other hand, it is found that radiation feedbacks (i.e., changes in the net radiative anomalies accompanying westerly wind bursts) are not essential for the development of WWBs, and act as a weak negative feedback on WWBs and their associated convection. Similarly, sensible surface heat flux anomalies are not found to have an effect on the development of model WWBs.

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