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Heat Transport Compensation in Atmosphere and Ocean over the Past 22,000 Years.

Yang H, Zhao Y, Liu Z, Li Q, He F, Zhang Q - Sci Rep (2015)

Bottom Line: A 22,000-year-long simulation using an ocean-atmosphere coupled model shows that the changes in atmosphere and ocean MHT are significant but tend to be out of phase in most regions, mitigating the total MHT change, which helps to maintain the stability of the Earth's overall climate.The simple model can reproduce qualitatively the evolution and compensation features of the MHT over the past 22,000 years.This study suggests that an internal mechanism may exist in the climate system, which might have played a role in constraining the global climate change over the past 22,000 years.

View Article: PubMed Central - PubMed

Affiliation: Laboratory for Climate and Ocean-Atmosphere Studies (LaCOAS) and Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing 100871, China.

ABSTRACT
The Earth's climate has experienced dramatic changes over the past 22,000 years; however, the total meridional heat transport (MHT) of the climate system remains stable. A 22,000-year-long simulation using an ocean-atmosphere coupled model shows that the changes in atmosphere and ocean MHT are significant but tend to be out of phase in most regions, mitigating the total MHT change, which helps to maintain the stability of the Earth's overall climate. A simple conceptual model is used to understand the compensation mechanism. The simple model can reproduce qualitatively the evolution and compensation features of the MHT over the past 22,000 years. We find that the global energy conservation requires the compensation changes in the atmosphere and ocean heat transports. The degree of compensation is mainly determined by the local climate feedback between surface temperature and net radiation flux at the top of the atmosphere. This study suggests that an internal mechanism may exist in the climate system, which might have played a role in constraining the global climate change over the past 22,000 years.

No MeSH data available.


Related in: MedlinePlus

AMOC, FWF and MHT.(a) The blue curve is the AMOC index, defined as the maximum value of the streamfunction over 20°–70°N and between 300–2000 m in the Atlantic (Units: Sv; 1 Sv = 106 m3s−1); red curve is the FWF (Sv), obtained by integrating the total meltwater flux over the North Atlantic between 35° and 70°N. The number in parentheses indicates the correlation coefficient between the AMOC and FWF. (b–e) Anomalous MHT averaged over different latitude bands (PW). The linear trends of heat transports over the whole 22 kyr are removed first, and then the mean values at 22 ka are subtracted. In (b–e) the black curve is the total MHT; red, the AHT; and blue, the OHT. The number in parentheses indicates correlation coefficient between AHT and OHT. The thick curves in (a–e) are the low-pass-filtered (150-year running mean) versions of the corresponding time series.
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f2: AMOC, FWF and MHT.(a) The blue curve is the AMOC index, defined as the maximum value of the streamfunction over 20°–70°N and between 300–2000 m in the Atlantic (Units: Sv; 1 Sv = 106 m3s−1); red curve is the FWF (Sv), obtained by integrating the total meltwater flux over the North Atlantic between 35° and 70°N. The number in parentheses indicates the correlation coefficient between the AMOC and FWF. (b–e) Anomalous MHT averaged over different latitude bands (PW). The linear trends of heat transports over the whole 22 kyr are removed first, and then the mean values at 22 ka are subtracted. In (b–e) the black curve is the total MHT; red, the AHT; and blue, the OHT. The number in parentheses indicates correlation coefficient between AHT and OHT. The thick curves in (a–e) are the low-pass-filtered (150-year running mean) versions of the corresponding time series.

Mentions: The stable total MHT results from the compensating changes in AHT and OHT, which is particularly clear during the OD (Fig. 2). The transient changes in MHTs, relative to the mean LGM state in 22 ka, are examined, together with variations in the AMOC and freshwater forcing in the North Atlantic (Methods). The changes in AHT and OHT compensated each other at most latitudes from the LGM to the OD; since then, the AHT and OHT remained negatively correlated though the compensation between them seems to fail (Fig. 2c–e). Figure 2 also shows that there is no compensation in the Northern Hemisphere between 50°–70°N (Fig. 2b). At these latitudes, the mean OHT can be neglected (Fig. 1) and the mean AHT is small when compared to that in the lower latitudes. Since the MHT in high latitudes plays a minor role in global energy balance, we will focus on compensation between AHT and OHT in lower latitudes in this paper.


Heat Transport Compensation in Atmosphere and Ocean over the Past 22,000 Years.

Yang H, Zhao Y, Liu Z, Li Q, He F, Zhang Q - Sci Rep (2015)

AMOC, FWF and MHT.(a) The blue curve is the AMOC index, defined as the maximum value of the streamfunction over 20°–70°N and between 300–2000 m in the Atlantic (Units: Sv; 1 Sv = 106 m3s−1); red curve is the FWF (Sv), obtained by integrating the total meltwater flux over the North Atlantic between 35° and 70°N. The number in parentheses indicates the correlation coefficient between the AMOC and FWF. (b–e) Anomalous MHT averaged over different latitude bands (PW). The linear trends of heat transports over the whole 22 kyr are removed first, and then the mean values at 22 ka are subtracted. In (b–e) the black curve is the total MHT; red, the AHT; and blue, the OHT. The number in parentheses indicates correlation coefficient between AHT and OHT. The thick curves in (a–e) are the low-pass-filtered (150-year running mean) versions of the corresponding time series.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4645171&req=5

f2: AMOC, FWF and MHT.(a) The blue curve is the AMOC index, defined as the maximum value of the streamfunction over 20°–70°N and between 300–2000 m in the Atlantic (Units: Sv; 1 Sv = 106 m3s−1); red curve is the FWF (Sv), obtained by integrating the total meltwater flux over the North Atlantic between 35° and 70°N. The number in parentheses indicates the correlation coefficient between the AMOC and FWF. (b–e) Anomalous MHT averaged over different latitude bands (PW). The linear trends of heat transports over the whole 22 kyr are removed first, and then the mean values at 22 ka are subtracted. In (b–e) the black curve is the total MHT; red, the AHT; and blue, the OHT. The number in parentheses indicates correlation coefficient between AHT and OHT. The thick curves in (a–e) are the low-pass-filtered (150-year running mean) versions of the corresponding time series.
Mentions: The stable total MHT results from the compensating changes in AHT and OHT, which is particularly clear during the OD (Fig. 2). The transient changes in MHTs, relative to the mean LGM state in 22 ka, are examined, together with variations in the AMOC and freshwater forcing in the North Atlantic (Methods). The changes in AHT and OHT compensated each other at most latitudes from the LGM to the OD; since then, the AHT and OHT remained negatively correlated though the compensation between them seems to fail (Fig. 2c–e). Figure 2 also shows that there is no compensation in the Northern Hemisphere between 50°–70°N (Fig. 2b). At these latitudes, the mean OHT can be neglected (Fig. 1) and the mean AHT is small when compared to that in the lower latitudes. Since the MHT in high latitudes plays a minor role in global energy balance, we will focus on compensation between AHT and OHT in lower latitudes in this paper.

Bottom Line: A 22,000-year-long simulation using an ocean-atmosphere coupled model shows that the changes in atmosphere and ocean MHT are significant but tend to be out of phase in most regions, mitigating the total MHT change, which helps to maintain the stability of the Earth's overall climate.The simple model can reproduce qualitatively the evolution and compensation features of the MHT over the past 22,000 years.This study suggests that an internal mechanism may exist in the climate system, which might have played a role in constraining the global climate change over the past 22,000 years.

View Article: PubMed Central - PubMed

Affiliation: Laboratory for Climate and Ocean-Atmosphere Studies (LaCOAS) and Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing 100871, China.

ABSTRACT
The Earth's climate has experienced dramatic changes over the past 22,000 years; however, the total meridional heat transport (MHT) of the climate system remains stable. A 22,000-year-long simulation using an ocean-atmosphere coupled model shows that the changes in atmosphere and ocean MHT are significant but tend to be out of phase in most regions, mitigating the total MHT change, which helps to maintain the stability of the Earth's overall climate. A simple conceptual model is used to understand the compensation mechanism. The simple model can reproduce qualitatively the evolution and compensation features of the MHT over the past 22,000 years. We find that the global energy conservation requires the compensation changes in the atmosphere and ocean heat transports. The degree of compensation is mainly determined by the local climate feedback between surface temperature and net radiation flux at the top of the atmosphere. This study suggests that an internal mechanism may exist in the climate system, which might have played a role in constraining the global climate change over the past 22,000 years.

No MeSH data available.


Related in: MedlinePlus