scholarly journals Multidecadal Polynya Formation in a Conceptual (Box) Model

2020 ◽  
Author(s):  
Daan Boot ◽  
René M. Van Westen ◽  
Henk A. Dijkstra
Keyword(s):  
Deep Convection ◽  
Subsurface Layer ◽  
Dominant Frequency ◽  
Box Model ◽  
Freshwater Flux ◽  
Heat Accumulation ◽  
Community Earth System Model ◽  
Maud Rise ◽  
Static Instability

Abstract. Maud Rise Polynyas (MRPs) form due to deep convection, which is caused by static instability of the water column. Recent studies with the Community Earth System Model (CESM) have indicated that a multidecadal varying heat accumulation in the subsurface layer occurs prior to MRP formation due to the heat transport over the Weddell gyre. In this study, a conceptual MRP box model, forced with CESM data, is used to investigate the role of this subsurface heat accumulation in MRP formation. Cases excluding and including multidecadal varying subsurface heat and salt fluxes are considered and multiple polynya events are only simulated in the cases where subsurface fluxes are included. The dominant frequency for MRP events in these results, approximately the frequency of the subsurface heat and salt accumulation, is still visible in cases where white noise is added to the freshwater flux. This indicates the importance and dominance of the subsurface heat accumulation in MRP formation.

scholarly journals Multidecadal polynya formation in a conceptual (box) model

Ocean Science ◽  
2021 ◽  
Vol 17 (1) ◽  
pp. 335-350
Author(s):  
Daan Boot ◽  
René M. van Westen ◽  
Henk A. Dijkstra
Keyword(s):  
Deep Convection ◽  
Subsurface Layer ◽  
Dominant Frequency ◽  
Box Model ◽  
System Model ◽  
Freshwater Flux ◽  
Heat Accumulation ◽  
Community Earth System Model ◽  
Maud Rise

Abstract. Maud Rise polynyas (MRPs) form due to deep convection, which is caused by static instabilities of the water column. Recent studies with the Community Earth System Model (CESM) have indicated that a multidecadal varying heat accumulation in the subsurface layer occurs prior to MRP formation due to the heat transport over the Weddell Gyre. In this study, a conceptual MRP box model, forced with CESM data, is used to investigate the role of this subsurface heat accumulation in MRP formation. Cases excluding and including multidecadal varying subsurface heat and salt fluxes are considered, and multiple polynya events are only simulated in the cases where subsurface fluxes are included. The dominant frequency for MRP events in these results, approximately the frequency of the subsurface heat and salt accumulation, is still visible in cases where white noise is added to the freshwater flux. This indicates the importance and dominance of the subsurface heat accumulation in MRP formation.

A new convective model for the Maud Rise Polynya

2020 ◽  
Author(s):  
Daan Boot ◽  
Rene van Westen ◽  
Henk Dijkstra
Keyword(s):  
Surface Layer ◽  
Deep Convection ◽  
Subsurface Layer ◽  
Heat Accumulation ◽  
Large Hole ◽  
Model Studies ◽  
Maud Rise ◽  
Model Set ◽  
Set Up ◽  
Convective Model

<p>The Maud Rise Polynya, a large hole in the Antarctic sea-ice, was first observed in the 1970s and reappeared again in 2017. The general paradigm is that the polynya formed due to deep convection caused by static instability of the water column. There is, however, no consensus on the processes responsible for the initialisation of deep convection. Both atmospheric and oceanic processes have been suggested by observational and model studies. Deep convection is viewed as an irregular event caused by densification of the surface layer. Heat accumulation in the subsurface layer is also considered to be vital for the formation of the polynya. This study investigates the initiation of deep convection using a simple 1D convective model introduced by Martinson et al. (1981) which is further extended with a dynamical subsurface layer. This extended version of the model allows us to study the contribution of both surface- and subsurface forcing on the initiation of deep convection. Two model set-ups with different subsurface characteristics have been used: (1) with a constant subsurface layer; (2) with periodic subsurface accumulation of heat and/or salt. Model set-up 1 results in either one or no polynya events. This does not agree with observations, since multiple polynya events have been observed. Model set-up 2 results in in periodically returning polynyas with the same period as the subsurface accumulation. Therefore, model set-up 2 is able to again multiple events as observed. Adding noise to the simulations does not change the conclusions for both model set-ups. The results suggest that subsurface forcing is a dominant process in Maud Rise Polynya formation. Our results indicate that densification of the surface layer plays a much smaller role than previously assumed by various literature. Based on these results and previous studies, we suggest that subsurface processes govern both the initial formation and reccurrence of the Maud Rise Polynya.</p>

scholarly journals A multi-box model study of the role of the biospheric metabolism in the recent decline of δ18O in atmospheric CO2

Tellus B ◽  
2002 ◽  
Vol 54 (4) ◽  
pp. 307-324
Author(s):  
Misa Ishizawa ◽  
Takakiyo Nakazawa ◽  
Kaz Higuchi
Keyword(s):  
Atmospheric Co2 ◽  
Box Model ◽  
Model Study

scholarly journals Understanding Bjerknes Compensation in Meridional Heat Transports and the Role of Freshwater in a Warming Climate

2018 ◽  
Vol 31 (12) ◽  
pp. 4791-4806 ◽  
Author(s):  
Qianzi Yang ◽  
Yingying Zhao ◽  
Qin Wen ◽  
Jie Yao ◽  
Haijun Yang
Keyword(s):  
Global Warming ◽  
North Atlantic ◽  
Coupled Model ◽  
Phase Changes ◽  
Box Model ◽  
Freshwater Flux ◽  
The North ◽  
Warming Climate ◽  
Transient Period ◽  
The North Atlantic

The Bjerknes compensation (BJC) under global warming is studied using a simple box model and a coupled Earth system model. The BJC states the out-of-phase changes in the meridional atmosphere and ocean heat transports. Results suggest that the BJC can occur during the transient period of global warming. During the transient period, the sea ice melting in the high latitudes can cause a significant weakening of the Atlantic meridional overturning circulation (AMOC), resulting in a cooling in the North Atlantic. The meridional contrast of sea surface temperature would be enhanced, and this can eventually enhance the Hadley cell and storm-track activities in the Northern Hemisphere. Accompanied by changes in both ocean and atmosphere circulations, the northward ocean heat transport in the Atlantic is decreased while the northward atmosphere heat transport is increased, and the BJC occurs in the Northern Hemisphere. Once the freshwater influx into the North Atlantic Ocean stops, or the ocean even loses freshwater because of strong heating in the high latitudes, the AMOC would recover. Both the atmosphere and ocean heat transports would be enhanced, and they can eventually recover to the state of the control run, leading to the BJC to become invalid. The above processes are clearly demonstrated in the coupled model CO2 experiment. Since it is difficult to separate the freshwater effect from the heating effect in the coupled model, a simple box model is used to understand the BJC mechanism and freshwater’s role under global warming. In a warming climate, the freshwater flux into the ocean can cool the global surface temperature, mitigating the temperature rise. Box model experiments indicate clearly that it is the freshwater flux into the North Atlantic that causes out-of-phase changes in the atmosphere and ocean heat transports, which eventually plays a stabilizing role in global climate change.

Carbon cycle response to Dansgaard-Oeschger events in a freely oscillating LGM setup of the Community Earth System Model.

2021 ◽  
Author(s):  
Markus Jochum ◽  
Zanna Chase ◽  
Roman Nutermn ◽  
Joel Pedro ◽  
Sune Rasmussen ◽  
...  
Keyword(s):  
North Atlantic ◽  
Deep Convection ◽  
Time Lags ◽  
Biological Productivity ◽  
The North ◽  
Community Earth System Model ◽  
Free Running ◽  
The North Atlantic ◽  
Set Up ◽  
The North Pacific

<p>We use a LGM setup of the CESM with marine and terrestrial biogeochemistry. This free-running  set-up (i.e., no freshwater hosing) exhibts Dansgaard-Oeschger events and Antarctic Isotope Maxima with time-lags and amplitudes that are consistent with paleo reconstructions. The CO2 signal associated DO events is also consistent with reconstructions: a 10 ppm/kyr increase during stadials, with the increase continuing some 400 years after Antarctica has started to cool again. An analysis of the modelled air-sea/land carbon fluxes reveals that some 3ppm of the stadial increase are due to shifting rain and temperature patterns that reduce growth of land vegetation. This adjustment is largely concluded after 3 centuries. The remainder of the signal is due to reduced ocean uptake. It turns out that reduced subduction of carbon in the Southern Ocean is mostly compensated by reduced upwelling in the equatorial oceans. Thus, as found in previous studies, much of the extra carbon is due to reduced uptake in the North Atlantic, partly directly due to reduced deep convection, and partly due to a reduced biological productivity because much of the North Atlantic nutrients are supplied by the AMOC. A big surprise is the emergence of the North Pacific as a major contributor to the changes in the air-fluxes of carbon. It is the reorganization of its wind-driven circulation that explains why global net-outgassing of carbon continues long after the interstadial has begun.</p>

A Language/Action Based Approach to Information Modelling

2011 ◽  
pp. 2386-2389
Author(s):  
Paul Johannesson
Keyword(s):  
Information System ◽  
Information Systems ◽  
Philosophy Of Language ◽  
Speech Acts ◽  
Systems Design ◽  
Box Model ◽  
Information Modelling ◽  
Functional Perspective ◽  
Data View

There are several different views of the role of information systems. Two of the most important are the data view and the communicative view. According to the data view, the primary purpose of an information system is to provide a model of a domain, thereby enabling people to obtain information about reality by studying the model. In this respect, an information system works as a repository of data that reflects the structure and behaviour of an enterprise, and the system provides data that can be used for decisions about the enterprise. In contrast, the communicative view states that the major role of an information system is to support communication within and between organisations by structuring and coordinating the actions performed by organisational agents. The system is seen as a medium through which people can perform social actions, such as stating facts, making promises, and giving orders. The data and communicative views of information systems are mirrored by two different views of organisations: the functional view and the constructional view (Dietz, 2003a). The functional view focuses on the functions of an organisation with respect to its environment, in particular, the resources that the organisation consumes and produces. A model of an organisation from a functional perspective is a black-box model, as it shows the interactions with the environment but not the internal mechanisms. The constructional view, on the other hand, focuses on how behaviour and function are brought about by the operations and structure of an organisation. A model of an organisation from a constructional perspective is a white-box model as it shows the inner workings of the organisation. In information systems design, the starting point has often been based on the data view and the functional view, though frequently augmented by concepts like reasoning and monitoring. However, these views easily lead to a computerand technology-biased management of the communication taking place in an organisation, and they benefit from being complemented by the communicative and constructional views. A promising theoretical foundation for these views is the language/action approach, which is based on theories from linguistics and the philosophy of language. In the language/action approach, business actions are modelled on the notions of speech acts and discourses, which provide a basis for distinguishing between different communication phases, such as preparation, negotiation, and acceptance. The purpose of this chapter is to outline how the language/action approach can be used as a basis for the information modelling of communicative aspects in organisations.

scholarly journals Mesoscale Processes during the Genesis of Hurricane Karl (2010)

2019 ◽  
Vol 76 (8) ◽  
pp. 2235-2255 ◽  
Author(s):  
Michael M. Bell ◽  
Michael T. Montgomery
Keyword(s):  
Structural Changes ◽  
Doppler Radar ◽  
Deep Convection ◽  
Tropical Cyclogenesis ◽  
Primary Role ◽  
Low Level ◽  
Stratiform Precipitation ◽  
Environmental Air ◽  
Mesoscale Processes

Abstract Observations from the Pre-Depression Investigation of Cloud Systems in the Tropics (PREDICT), Genesis and Rapid Intensification Processes (GRIP), and Intensity Forecast Experiment (IFEX) field campaigns are analyzed to investigate the mesoscale processes leading to the tropical cyclogenesis of Hurricane Karl (2010). Research aircraft missions provided Doppler radar, in situ flight level, and dropsonde data documenting the structural changes of the predepression disturbance. Following the pre-Karl wave pouch, variational analyses at the meso-β and meso-α scales suggest that the convective cycle in Karl alternately built the low- and midlevel circulations leading to genesis episodically rather than through a sustained lowering of the convective mass flux from increased stabilization. Convective bursts that erupt in the vorticity-rich environment of the recirculating pouch region enhance the low-level meso-β- and meso-α-scale circulation through vortex stretching. As the convection wanes, the resulting stratiform precipitation strengthens the midlevel circulation through convergence associated with ice microphysical processes, protecting the disturbance from the intrusion of dry environmental air. Once the column saturation fraction returns to a critical value, a subsequent convective burst below the midlevel circulation further enhances the low-level circulation, and the convective cycle repeats. The analyses suggest that the onset of deep convection and associated low-level spinup were closely related to the coupling of the vorticity and moisture fields at low and midlevels. Our interpretation of the observational analysis presented in this study reaffirms a primary role of deep convection in the genesis process and provides a hypothesis for the supporting role of stratiform precipitation and the midlevel vortex.

scholarly journals A Drift-Free Decadal Climate Prediction System for the Community Earth System Model

2019 ◽  
Vol 32 (18) ◽  
pp. 5967-5995 ◽  
Author(s):  
Yoshimitsu Chikamoto ◽  
Axel Timmermann ◽  
Matthew J. Widlansky ◽  
Shaoqing Zhang ◽  
Magdalena A. Balmaseda
Keyword(s):  
Three Dimensional ◽  
Climate Prediction ◽  
System Model ◽  
Prediction System ◽  
Ocean Temperature ◽  
Perfect Model ◽  
Community Earth System Model ◽  
Decadal Climate ◽  
Decadal Climate Prediction

Abstract Performance of a newly developed decadal climate prediction system is examined using the low-resolution Community Earth System Model (CESM). To identify key sources of predictability and determine the role of upper and deeper ocean data assimilation, we first conduct a series of perfect model experiments. These experiments reveal the importance of upper ocean temperature and salinity assimilation in reducing sea surface temperature biases. However, to reduce biases in the sea surface height, data assimilation below 300 m in the ocean is necessary, in particular for high-latitude regions. The perfect model experiments clearly emphasize the key role of combined three-dimensional ocean temperature and salinity assimilation in reproducing mean state and model trajectories. Applying this knowledge to the realistic decadal climate prediction system, we conducted an ensemble of ocean assimilation simulations with the fully coupled CESM covering the period 1960–2014. In this system, we assimilate three-dimensional ocean temperature and salinity data into the ocean component of CESM. Instead of assimilating direct observations, we assimilate temperature and salinity anomalies obtained from the ECMWF Ocean Reanalysis version 4 (ORA-S4). Anomalies are calculated relative to the sum of the ORA-S4 climatology and an estimate of the externally forced signal. As a result of applying the balanced ocean conditions to the model, our hindcasts show only very little drift and initialization shocks. This new prediction system exhibits multiyear predictive skills for decadal climate variations of the Atlantic meridional overturning circulation (AMOC) and North Pacific decadal variability.

The North Pacific Pacemaker Effect on Historical ENSO and Its Mechanisms

2019 ◽  
Vol 32 (22) ◽  
pp. 7643-7661 ◽  
Author(s):  
Dillon J. Amaya ◽  
Yu Kosaka ◽  
Wenyu Zhou ◽  
Yu Zhang ◽  
Shang-Ping Xie ◽  
...  
Keyword(s):  
El Niño ◽  
North Pacific ◽  
El Nino ◽  
Southern Oscillation ◽  
Deep Convection ◽  
Boreal Summer ◽  
Enso Events ◽  
The North ◽  
The North Pacific

Abstract Studies have indicated that North Pacific sea surface temperature (SST) variability can significantly modulate El Niño–Southern Oscillation (ENSO), but there has been little effort to put extratropical–tropical interactions into the context of historical events. To quantify the role of the North Pacific in pacing the timing and magnitude of observed ENSO, we use a fully coupled climate model to produce an ensemble of North Pacific Ocean–Global Atmosphere (nPOGA) SST pacemaker simulations. In nPOGA, SST anomalies are restored back to observations in the North Pacific (>15°N) but are free to evolve throughout the rest of the globe. We find that the North Pacific SST has significantly influenced observed ENSO variability, accounting for approximately 15% of the total variance in boreal fall and winter. The connection between the North and tropical Pacific arises from two physical pathways: 1) a wind–evaporation–SST (WES) propagating mechanism, and 2) a Gill-like atmospheric response associated with anomalous deep convection in boreal summer and fall, which we refer to as the summer deep convection (SDC) response. The SDC response accounts for 25% of the observed zonal wind variability around the equatorial date line. On an event-by-event basis, nPOGA most closely reproduces the 2014/15 and the 2015/16 El Niños. In particular, we show that the 2015 Pacific meridional mode event increased wind forcing along the equator by 20%, potentially contributing to the extreme nature of the 2015/16 El Niño. Our results illustrate the significant role of extratropical noise in pacing the initiation and magnitude of ENSO events and may improve the predictability of ENSO on seasonal time scales.

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