Local Meridional Circulation and Deserts

2001 ◽  
Vol 18 (5) ◽  
pp. 864-872 ◽  
Author(s):  
Liu Ping ◽  
Wu Guoxiong ◽  
Sun Shufen
Keyword(s):  
Meridional Circulation ◽  
Local Meridional Circulation

Impacts of the Madden-Julian Oscillation on South China Sea Monsoon

2020 ◽  
Author(s):  
Qun Zhou ◽  
Lixin Wei
Keyword(s):  
South China Sea ◽  
South China ◽  
Meridional Circulation ◽  
East Asian ◽  
Winter Monsoon ◽  
Western Pacific ◽  
Madden Julian Oscillation ◽  
China Sea ◽  
The Western Pacific ◽  
Local Meridional Circulation

Abstract It is of great practical importance to understand the variability of the South China Sea (SCS) monsoon on intraseasonal time scales, since the anomalous enhancement of the SCS monsoon may exert serious impacts on the safety of offshore engineering and marine transportation. Our composite analysis shows that the SCS surface wind anomalies are considerably varying with the Madden-Julian Oscillation (MJO) eastward propagation. The SCS summer southwest monsoon tends to be stronger (weaker) in phases 5–8 (1–4) of MJO with the largest positive (negative) wind-speed anomalies when the MJO convection is centered in the western Pacific (far western Indian Ocean), suggesting the highest (lowest) probability of the gale over the SCS. The variation of the western Pacific Subtropical High (WPSH), induced by the variations of the local meridional circulation, is shown to play a crucial role in the MJO-SCS summer monsoon linkage. The SCS winter monsoon is also shown to be modulated by the MJO with strengthened (weakened) surface northeasterly in phases 5–6 (1–2). The extra-tropical East Asian trough and East Asian westerly jet associated with the local meridional circulation can well explain the changes of the MJO-SCS winter monsoon relationship. The opposite responses of the wind direction during the same phases of the MJO between summer and winter may be attributed to the discrepancy of meridional circulation related to the wintertime equatorward shift of the MJO convection. The present study indicates that the MJO could be taken into consideration when applying extended-range weather forecast over the SCS as the predictability of the MJO activity is up to 15–20 day currently.

Meridional Circulation, Turbulence, and Diffusion Processes in Stars

1976 ◽  
Vol 32 ◽  
pp. 109-116 ◽  
Author(s):  
S. Vauclair
Keyword(s):  
Convection Zone ◽  
Diffusion Processes ◽  
Meridional Circulation ◽  
Diffusion Time ◽  
Work In Progress ◽  
First Results ◽  
Stellar Envelopes ◽  
And Diffusion ◽  
Turbulence And Diffusion ◽  
Hr Diagram

This paper gives the first results of a work in progress, in collaboration with G. Michaud and G. Vauclair. It is a first attempt to compute the effects of meridional circulation and turbulence on diffusion processes in stellar envelopes. Computations have been made for a 2 Mʘstar, which lies in the Am - δ Scuti region of the HR diagram.Let us recall that in Am stars diffusion cannot occur between the two outer convection zones, contrary to what was assumed by Watson (1970, 1971) and Smith (1971), since they are linked by overshooting (Latour, 1972; Toomre et al., 1975). But diffusion may occur at the bottom of the second convection zone. According to Vauclair et al. (1974), the second convection zone, due to He II ionization, disappears after a time equal to the helium diffusion time, and then diffusion may happen at the bottom of the first convection zone, so that the arguments by Watson and Smith are preserved.

scholarly journals Polar Middle Atmospheric Responses to Medium Energy Electron (MEE) Precipitation Using Numerical Model Simulations

Atmosphere ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 133
Author(s):  
Ji-Hee Lee ◽  
Geonhwa Jee ◽  
Young-Sil Kwak ◽  
Heejin Hwang ◽  
Annika Seppälä ◽  
...  
Keyword(s):  
Climate Model ◽  
Middle Atmosphere ◽  
Meridional Circulation ◽  
Stratospheric Ozone ◽  
High Energy ◽  
Chemical Changes ◽  
Temperature Changes ◽  
Mesospheric Temperature ◽  
High Energy Electrons ◽  
Circulation Changes

Energetic particle precipitation (EPP) is known to be an important source of chemical changes in the polar middle atmosphere in winter. Recent modeling studies further suggest that chemical changes induced by EPP can also cause dynamic changes in the middle atmosphere. In this study, we investigated the atmospheric responses to the precipitation of medium-to-high energy electrons (MEEs) over the period 2005–2013 using the Specific Dynamics Whole Atmosphere Community Climate Model (SD-WACCM). Our results show that the MEE precipitation significantly increases the amounts of NOx and HOx, resulting in mesospheric and stratospheric ozone losses by up to 60% and 25% respectively during polar winter. The MEE-induced ozone loss generally increases the temperature in the lower mesosphere but decreases the temperature in the upper mesosphere with large year-to-year variability, not only by radiative effects but also by adiabatic effects. The adiabatic effects by meridional circulation changes may be dominant for the mesospheric temperature changes. In particular, the meridional circulation changes occasionally act in opposite ways to vary the temperature in terms of height variations, especially at around the solar minimum period with low geomagnetic activity, which cancels out the temperature changes to make the average small in the polar mesosphere for the 9-year period.

scholarly journals Disruption of the Atlantic Meridional Circulation during Deglacial Climates Inferred from Planktonic Foraminiferal Shell Weights

2021 ◽  
Vol 9 (5) ◽  
pp. 519
Author(s):  
Stergios D. Zarkogiannis
Keyword(s):  
Atlantic Ocean ◽  
Meridional Circulation ◽  
Order Approximation ◽  
Planktonic Foraminifera ◽  
Sediment Cores ◽  
Meridional Overturning Circulation ◽  
Density Structure ◽  
Last Interglacial ◽  
Shell Weight ◽  
The North

Changes in the density structure of the upper oceanic water masses are an important forcing of changes in the Atlantic Meridional Overturning Circulation (AMOC), which is believed to widely affect Earth’s climate. However, very little is known about past changes in the density structure of the Atlantic Ocean, despite being extensively studied. The physical controls on planktonic foraminifera calcification are explored here, to obtain a first-order approximation of the horizontal density gradient in the eastern Atlantic during the last 200,000 years. Published records of Globigerina bulloides shells from the North and Tropical eastern Atlantic were complemented by the analysis of a South Atlantic core. The masses of the same species shells from three different dissolution assessed sediment cores along the eastern Atlantic Ocean were converted to seawater density values using a calibration equation. Foraminifera, as planktonic organisms, are subject to the physical properties of the seawater and thus their shells are sensitive to buoyancy forcing through surface temperature and salinity perturbations. By using planktonic foraminifera shell weight as an upper ocean density proxy, two intervals of convergence of the shell masses are identified during cold intervals of the last two deglaciations that may be interpreted as weak ocean density gradients, indicating nearly or completely eliminated meridional circulation, while interhemispheric Atlantic density differences appear to alleviate with the onset of the last interglacial. The results confirm the significance of variations in the density of Atlantic surface waters for meridional circulation changes.

scholarly journals Effects of surface magnetic activity on meridional circulation measurements

2008 ◽  
Vol 118 ◽  
pp. 012081
Author(s):  
Irene González Hernández ◽  
Shukur Kholikov ◽  
Frank Hill ◽  
Rachel Howe ◽  
Rudolph Komm
Keyword(s):  
Meridional Circulation ◽  
Magnetic Activity

scholarly journals Meridional circulation dynamics in a cyclic convective dynamo

2017 ◽  
Vol 607 ◽  
pp. A120 ◽  
Author(s):  
D. Passos ◽  
M. Miesch ◽  
G. Guerrero ◽  
P. Charbonneau
Keyword(s):  
Meridional Circulation ◽  
Circulation Dynamics

scholarly journals Abundances anomalies and meridional circulation in horizontal branch stars

2009 ◽  
Vol 500 (3) ◽  
pp. 1163-1171 ◽  
Author(s):  
D. Quievy ◽  
P. Charbonneau ◽  
G. Michaud ◽  
J. Richer
Keyword(s):  
Meridional Circulation ◽  
Horizontal Branch ◽  
Horizontal Branch Stars

On the Determination of Age of Air Trends from Atmospheric Trace Species

2011 ◽  
Vol 68 (1) ◽  
pp. 139-154 ◽  
Author(s):  
Rolando R. Garcia ◽  
William J. Randel ◽  
Douglas E. Kinnison
Keyword(s):  
Climate Model ◽  
Meridional Circulation ◽  
Transport Model ◽  
Numerical Models ◽  
Chemical Species ◽  
Large Error ◽  
Atmospheric Concentration ◽  
Nonlinear Growth ◽  
Mean Meridional Circulation ◽  
The Mean

Abstract Trace chemical species have been used in numerical models to calculate the age of air (AOA), which is a measure of the strength of the mean meridional circulation. The trend in the AOA has also been computed and found to be negative in simulations where greenhouse gases increase with time, which is consistent with the acceleration of the mean meridional circulation calculated under these conditions. This modeling result has been tested recently using observations of SF6, a very long lived species whose atmospheric concentration has increased rapidly over the last half century, and of CO2, which is also very long lived and increasing with time. Surprisingly, the AOA estimated from these gases exhibits no significant trend over the period 1975–2005. Here the Whole Atmosphere Community Climate Model (WACCM) is used to derive estimates of the AOA from SF6 and CO2 over the period 1965–2006. The calculated AOA yields trends that are smaller than the trend derived from a synthetic, linearly growing tracer, even after accounting for the nonlinear growth rates of SF6 and CO2. A simplified global transport model and analytical arguments are used to show that this follows from the variable growth rate of these species. It is also shown that, when AOA is sampled sparsely as in the observations, the resulting trends have very large error bars and are statistically undistinguishable from zero. These results suggest that trends in the AOA are difficult to estimate unambiguously except for well-sampled tracers that increase linearly and uniformly. While such tracers can be defined in numerical models, there are no naturally occurring species that exhibit such idealized behavior.

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