scholarly journals Modulation of the Extratropical Circulation by Combined Activity of the Madden–Julian Oscillation and Equatorial Rossby Waves during Boreal Winter

2013 ◽  
Vol 141 (4) ◽  
pp. 1347-1357 ◽  
Author(s):  
Lawrence C. Gloeckler ◽  
Paul E. Roundy
Keyword(s):  
Atmospheric Circulation ◽  
Rossby Waves ◽  
Deep Convection ◽  
Boreal Winter ◽  
Madden Julian Oscillation ◽  
Wave State ◽  
Empirical Prediction ◽  
Global Atmospheric Circulation ◽  
The Tropics ◽  
Extratropical Circulation

Abstract Time indices of the Madden–Julian oscillation (MJO) are often used to generate empirical forecasts of the global atmospheric circulation. Moist deep convection associated with the MJO initiates eastward-propagating Rossby waves that disperse into the midlatitudes. The background circulation then guides extratropical waves back into the tropics of the eastern Pacific Ocean. Previous works have shown that equatorial Rossby (ER) waves occur following intrusion of extratropical Rossby waves into the tropics. Westward-propagating ER waves and the MJO modulate the total convection. This convection modulates the zonal wind, which influences the location and existence of westerly wind ducts. These wind ducts, in turn, guide extratropical waves into the tropics. This paper demonstrates through a simple composite analysis that a simultaneous assessment of MJO and ER waves yields more information about the extratropical circulation during boreal winter than can be obtained based on either type of disturbance alone, or from a sum of the signals associated with the MJO and ER waves composited separately. This analysis, together with previous results, suggests a feedback loop between the MJO, these waves, and the extratropical circulation. Thus, assessment of the ER wave state during a particular phase of the MJO might yield better empirical prediction of the global atmospheric circulation that follows.

Zonal Wave 3 Pattern in the Southern Hemisphere generated by tropical convection

2021 ◽  
Author(s):  
Rishav Goyal ◽  
Martin Jucker ◽  
Alex Sen Gupta ◽  
Harry Hendon ◽  
Matthew England
Keyword(s):  
Sea Ice ◽  
Atmospheric Circulation ◽  
Southern Hemisphere ◽  
Ocean Circulation ◽  
General Circulation ◽  
Deep Convection ◽  
Circulation Model ◽  
Hadley Cell ◽  
Wave Source ◽  
The Tropics

Abstract A distinctive feature of the Southern Hemisphere (SH) extratropical atmospheric circulation is the quasi-stationary zonal wave 3 (ZW3) pattern, characterized by three high and three low-pressure centers around the SH extratropics. This feature is present in both the mean atmospheric circulation and its variability on daily, seasonal and interannual timescales. While the ZW3 pattern has significant impacts on meridional heat transport and Antarctic sea ice extent, the reason for its existence remains uncertain, although it has long been assumed to be linked to the existence of three major land masses in the SH extratropics. Here we use an atmospheric general circulation model to show that the stationery ZW3 pattern is instead driven by zonal asymmetric deep atmospheric convection in the tropics, with little to no role played by the orography or land masses in the extratropics. Localized regions of deep convection in the tropics form a local Hadley cell which in turn creates a wave source in the subtropics that excites a poleward and eastward propagating wave train which forms stationary waves in the SH high latitudes. Our findings suggest that changes in tropical deep convection, either due to natural variability or climate change, will impact the zonal wave 3 pattern, with implications for Southern Hemisphere climate, ocean circulation, and sea-ice.

scholarly journals Oceanic Impetus for Convective Onset of the Madden–Julian Oscillation in the Western Indian Ocean

2017 ◽  
Vol 30 (11) ◽  
pp. 4299-4316 ◽  
Author(s):  
Adam V. Rydbeck ◽  
Tommy G. Jensen
Keyword(s):  
Boundary Layer ◽  
Indian Ocean ◽  
Atmospheric Boundary Layer ◽  
Rossby Waves ◽  
Deep Convection ◽  
Western Indian Ocean ◽  
Convection Boundary Layer ◽  
Madden Julian Oscillation ◽  
Sst Gradient ◽  
Equatorial Rossby Waves

Abstract A theory for intraseasonal atmosphere–ocean–atmosphere feedback is supported whereby oceanic equatorial Rossby waves are partly forced in the eastern Indian Ocean by the Madden–Julian oscillation (MJO), reemerge in the western Indian Ocean ~70 days later, and force large-scale convergence in the atmospheric boundary layer that precedes MJO deep convection. Downwelling equatorial Rossby waves permit high sea surface temperature (SST) and enhance meridional and zonal SST gradients that generate convergent circulations in the atmospheric boundary layer. The magnitude of the SST and SST gradient increases are 0.25°C and 1.5°C Mm−1 (1 megameter is equal to 1000 km), respectively. The atmospheric circulations driven by the SST gradient are estimated to be responsible for up to 45% of the intraseasonal boundary layer convergence observed in the western Indian Ocean. The SST-induced boundary layer convergence maximizes 3–4 days prior to the convective maximum and is hypothesized to serve as a trigger for MJO deep convection. Boundary layer convergence is shown to further augment deep convection by locally increasing boundary layer moisture. Warm SST anomalies facilitated by downwelling equatorial Rossby waves are also associated with increased surface latent heat fluxes that occur after MJO convective onset. Finally, generation of the most robust downwelling equatorial Rossby waves in the western Indian Ocean is shown to have a distinct seasonal distribution.

scholarly journals Tropospheric methane in the tropics – first year from IASI hyperspectral infrared observations

2009 ◽  
Vol 9 (17) ◽  
pp. 6337-6350 ◽  
Author(s):  
C. Crevoisier ◽  
D. Nobileau ◽  
A. M. Fiore ◽  
R. Armante ◽  
A. Chédin ◽  
...  
Keyword(s):  
Seasonal Cycle ◽  
Atmospheric Transport ◽  
Deep Convection ◽  
High Spectral Resolution ◽  
Boreal Winter ◽  
Monsoon Period ◽  
Transport Pathways ◽  
Geographical Patterns ◽  
Methane Distribution ◽  
The Tropics

Abstract. Simultaneous observations from the Infrared Atmospheric Sounding Interferometer (IASI) and from the Advanced Microwave Sounding Unit (AMSU), launched together onboard the European MetOp platform in October 2006, are used to retrieve a mid-to-upper tropospheric content of methane (CH4) in clear-sky conditions, in the tropics, over sea, for the first 16 months of operation of MetOp (July 2007–October 2008). With its high spectral resolution, IASI provides nine channels in the 7.7 μm band highly sensitive to CH4 with reduced sensitivities to other atmospheric variables. These channels, sensitive to both CH4 and temperature, are used in conjunction with AMSU channels, only sensitive to temperature, to decorrelate both signals through a non-linear inference scheme based on neural networks. A key point of this approach is that no use is made of prior information in terms of methane seasonality, trend, or geographical patterns. The precision of the retrieval is estimated to be about 16 ppbv (~0.9%). Features of the retrieved methane space-time distribution include: (1) a strong seasonal cycle of 30 ppbv in the northern tropics with a maximum in January–March and a minimum in July–September, and a flat seasonal cycle in the southern tropics, in agreement with in-situ measurements; (2) a latitudinal decrease of 30 ppbv from 20° N to 20° S, in boreal spring and summer, lower than what is observed at the surface but in excellent agreement with tropospheric aircraft measurements; (3) geographical patterns in good agreement with simulations from the atmospheric transport and chemistry model MOZART-2, but with a higher variability and a higher concentration in boreal winter; (4) signatures of CH4 emissions transported to the middle troposphere such as a large plume of elevated tropospheric methane south of the Asian continent, which might be due to Asian emissions from rice paddies uplifted by deep convection during the monsoon period and then transported towards Indonesia. In addition to bringing a greatly improved view of methane distribution, these results from IASI should provide a means to observe and understand atmospheric transport pathways of methane from the surface to the upper troposphere.

scholarly journals Sensitivities of the MJO Forecasts on Configurations of Physics in the ECMWF Global Model

2020 ◽  
Author(s):  
Jun-Ichi Yano ◽  
Nils P. Wedi
Keyword(s):  
Diabatic Heating ◽  
Rossby Waves ◽  
Deep Convection ◽  
Global Model ◽  
Rapid Decay ◽  
Free Wave ◽  
Eddy Diffusivities ◽  
The Tropics

Abstract. Sensitivities of MJO forecasts to various different configurations of physics are examined with the ECMWF global model, IFS. A motivation behind this study is to explore a possibility of interpreting the MJO as a nonlinear free wave under active interactions with Rossby waves from and to higher latitudes. With this motivation in mind, various momentum dissipation terms as well as diabatic heating are selectively turned off over the tropics for the range of the latitudes 20° S–20° N, and it is examined how physical tendencies control the MJO dynamics. The former include eddy diffusivities as well as dissipations by both shallow and deep convection. The reduction of momentum dissipations tends to improve the MJO forecasts, but the effects are hardly additive, and their total removals rather lead to a rapid decay of the MJO, illustrating the complexity of interactions between the physics.

scholarly journals Boreal Winter Links between the Madden–Julian Oscillation and the Arctic Oscillation

2008 ◽  
Vol 21 (12) ◽  
pp. 3040-3050 ◽  
Author(s):  
Michelle L. L’Heureux ◽  
R. Wayne Higgins
Keyword(s):  
Arctic Oscillation ◽  
Active Phase ◽  
Temperature Fields ◽  
The Arctic ◽  
Boreal Winter ◽  
Madden Julian Oscillation ◽  
Global Circulation ◽  
Leading Mode ◽  
The Arctic Oscillation ◽  
The Tropics

Abstract There is increasing evidence that the Madden–Julian oscillation (MJO) modifies the mid- to high-latitude circulation and, in particular, appears to have a relationship to the leading mode of extratropical variability, the Arctic Oscillation (AO). In this study, new insights into the observed similarities between the MJO and the AO are explored. It is shown that the eastward progression of the convectively active phase of the MJO is associated with a corresponding shift in the tendency and sign of the AO index. Moreover, the AO and the MJO share several analogous features not only in the global circulation, but also in surface temperature fields. Also, the AO is linked to a pattern of eastward-propagating MJO-like variability in the tropics that is partially reproduced in free runs of the NCEP Climate Forecast System (CFS) model. Finally, it is shown that the structure of the AO, as defined by the leading mode in the 1000-hPa geopotential height field, is significantly altered based on the phase of the MJO.

scholarly journals A new insight on tropospheric methane in the Tropics – first year from IASI hyperspectral infrared observations

2009 ◽  
Vol 9 (2) ◽  
pp. 6855-6887 ◽  
Author(s):  
C. Crevoisier ◽  
D. Nobileau ◽  
A. M. Fiore ◽  
R. Armante ◽  
A. Chédin ◽  
...  
Keyword(s):  
Seasonal Cycle ◽  
Atmospheric Transport ◽  
Deep Convection ◽  
High Spectral Resolution ◽  
Boreal Winter ◽  
Monsoon Period ◽  
Transport Pathways ◽  
Geographical Patterns ◽  
Methane Distribution ◽  
The Tropics

Abstract. Simultaneous observations from the Infrared Atmospheric Sounding Interferometer (IASI) and from the Advanced Microwave Sounding Unit (AMSU), launched together onboard the European MetOp platform in October 2006, are used to retrieve a mid-to-upper tropospheric content of methane (CH4) in clear-sky conditions, in the Tropics, over sea, for the first 16 months of operation of MetOp (July 2007–October 2008). With its very high spectral resolution, IASI provides nine channels in the 7.7 μm band highly sensitive to CH4 with reduced sensitivities to other atmospheric variables. These channels, sensitive to both CH4 and temperature, are used in conjunction with AMSU channels, only sensitive to temperature, to decorrelate both signals through a non-linear inference scheme based on neural networks. A key point of this approach is that no use is made of prior information in terms of methane seasonality, trend, or geographical patterns. The accuracy of the retrieval is estimated to be about 16 ppbv (~0.9%). Features of the retrieved methane space-time distribution include: (1) a strong seasonal cycle of 30 ppbv in the Northern Tropics with a maximum in January–March and a minimum in July–September, and a flat seasonal cycle in the Southern Tropics, in agreement with in-situ measurements; (2) a latitudinal decrease of 30 ppbv from 20° N to 20° S, in boreal spring and summer, lower than what is observed at the surface but in excellent agreement with tropospheric aircraft measurements; (3) geographical patterns in good agreement with simulations from the atmospheric transport and chemistry model MOZART-2, but with a higher variability and a higher concentration in boreal winter; (4) signatures of CH4 emissions transported to the middle troposphere such as a large plume of elevated tropospheric methane south of the Asian continent, which might be due to Asian emissions from rice paddies uplifted by deep convection during the monsoon period and then transported towards Indonesia. In addition to bringing a greatly improved view of methane distribution, these results from IASI should provide a means to observe and understand atmospheric transport pathways of methane from the surface to the upper troposphere.

scholarly journals Mapping the Relationship between Northern Hemisphere Winter Surface Air Temperature and the Madden–Julian Oscillation

2011 ◽  
Vol 139 (8) ◽  
pp. 2439-2454 ◽  
Author(s):  
Yang Zhou ◽  
Keith R. Thompson ◽  
Youyu Lu
Keyword(s):  
North America ◽  
Linear Model ◽  
Air Temperature ◽  
Surface Air Temperature ◽  
Boreal Winter ◽  
Eastern North America ◽  
Madden Julian Oscillation ◽  
State Variables ◽  
Normal Surface ◽  
The Tropics

AbstractA regression-based modeling approach is described for mapping the dependence of atmospheric state variables such as surface air temperature (SAT) on the Madden–Julian oscillation (MJO). For the special case of a linear model the dependence can be described by two maps corresponding to the amplitude and lag of the mean atmospheric response with respect to the MJO. In this sense the method leads to a more parsimonious description than traditional compositing, which usually results in eight maps, one for each MJO phase. Another advantage of the amplitude and phase maps is that they clearly identify propagating signals, and also regions where the response is strongly amplified or attenuated. A straightforward extension of the linear model is proposed to allow the amplitude and phase of the response to vary with the amplitude of the MJO or indices that define the background state of the atmosphere–ocean system. Application of the approach to global SAT for boreal winter clearly shows the propagation of MJO-related signals in both the tropics and extratropics and an enhanced response over eastern North America and Alaska (further enhanced during La Niña years). The SAT response over Alaska and eastern North America is caused mainly by horizontal advection related to variations in shore-normal surface winds that, in turn, can be traced (via signals in the 500-hPa geopotential height) back to MJO-related disturbances in the tropics.

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