The excitation of the Madden-Julian Oscillation in atmospheric adjustment to equatorial heating

2021 ◽  
Author(s):  
Yu Liang ◽  
Alexey V. Fedorov ◽  
Vladimir Zeitlin ◽  
Patrick Haertel
Keyword(s):  
Intraseasonal Variability ◽  
Equatorial Indian Ocean ◽  
Circulation Pattern ◽  
Atmospheric Model ◽  
Surface Heating ◽  
Convective Heating ◽  
Madden Julian Oscillation ◽  
Aspect Ratios ◽  
Budget Analysis ◽  
Circulation Characteristic

AbstractWe study the adjustment of the tropical atmosphere to localized surface heating using a Lagrangian atmospheric model (LAM) that simulates a realistic Madden-Julian Oscillation (MJO) – the dominant, eastward-propagating mode of tropical intraseasonal variability modulating atmospheric convection. Idealized warm sea surface temperature (SST) anomalies of different aspect ratios and magnitudes are imposed in the equatorial Indian Ocean during MJO-neutral conditions and then maintained for 15 days. Throughout these experiments, we observe a robust generation of an MJO event, evident in precipitation, velocity, temperature and moisture fields, which becomes a key element of atmospheric adjustment along with the expected Kelvin and Rossby waves. The MJO circulation pattern gradually builds up during the first week, and then starts to propagate eastward at a speed of 5-7m/s. The upper-level quadrupole circulation characteristic of the MJO becomes evident around day 14, with two anticyclonic gyres generated by the Gill-type response to convective heating and two cyclonic gyres forced by the excited Kelvin waves and extratropical Rossby wave trains. A moisture budget analysis shows that the eastward propagation of the MJO is controlled largely by the anomalous advection of moisture and by the residual between anomalous moisture accumulation due to converging winds and precipitation. The initial MJO event is followed by successive secondary events, maintaining the MJO for several more cycles. Thus, this study highlights the fundamental role that the MJO can play in the adjustment of the moist equatorial atmosphere to localized surface heating.

Moistening Processes before the Convective Initiation of Madden–Julian Oscillation Events during the CINDY2011/DYNAMO Period

2015 ◽  
Vol 143 (2) ◽  
pp. 622-643 ◽  
Author(s):  
Tomoe Nasuno ◽  
Tim Li ◽  
Kazuyoshi Kikuchi
Keyword(s):  
Indian Ocean ◽  
High Frequency ◽  
Intraseasonal Variability ◽  
Equatorial Indian Ocean ◽  
Precipitable Water ◽  
Madden Julian Oscillation ◽  
Convective Initiation ◽  
Moisture Advection ◽  
Order Of Magnitude ◽  
Ecmwf Reanalysis

Abstract Convective initiation processes in the Madden–Julian oscillation (MJO) events that occurred during the Cooperative Indian Ocean Experiment on Intraseasonal Variability in the Year 2011 (CINDY2011)/Dynamics of the Madden–Julian Oscillation (DYNAMO) intensive observation period (IOP) were investigated. Two episodes that were initiated in mid-October (MJO1) and mid-November (MJO2) 2011 were analyzed using European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis and satellite data. Moisture budgets in the equatorial Indian Ocean (IO) domain (10°S–10°N, 60°–90°E) were analyzed in detail by separating each variable into basic-state (>80 day), intraseasonal (20–80 day), and high-frequency (<20 day) variations. The quality of the ECMWF reanalysis was also evaluated against the sounding data collected during the field campaign. In both MJO events, the increase in precipitable water started 8–9 days prior to the convective initiation. Moisture advection decomposition revealed that advection of basic moisture by intraseasonal easterly anomalies and of intraseasonal moisture anomalies by the basic zonal wind were pronounced in these two events. The nonlinear high-frequency terms in the meridional moisture advection were the same order of magnitude as the primary term in the middle troposphere, implying systematic upscale transport of moisture. As a possible mechanism of the acceleration of easterly anomalies, amplification of off-equatorial Rossby wave trains that intruded into the equatorial zone was detected during the preconditioning periods in both MJO events.

scholarly journals Coupled Impacts of the Diurnal Cycle of Sea Surface Temperature on the Madden–Julian Oscillation

2014 ◽  
Vol 27 (22) ◽  
pp. 8422-8443 ◽  
Author(s):  
Hyodae Seo ◽  
Aneesh C. Subramanian ◽  
Arthur J. Miller ◽  
Nicholas R. Cavanaugh
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Diurnal Cycle ◽  
Atmospheric Model ◽  
Sea Surface ◽  
Madden Julian Oscillation ◽  
Sst Variability ◽  
Budget Analysis ◽  
Diurnal Sst Variation

Abstract This study quantifies, from a systematic set of regional ocean–atmosphere coupled model simulations employing various coupling intervals, the effect of subdaily sea surface temperature (SST) variability on the onset and intensity of Madden–Julian oscillation (MJO) convection in the Indian Ocean. The primary effect of diurnal SST variation (dSST) is to raise time-mean SST and latent heat flux (LH) prior to deep convection. Diurnal SST variation also strengthens the diurnal moistening of the troposphere by collocating the diurnal peak in LH with those of SST. Both effects enhance the convection such that the total precipitation amount scales quasi-linearly with preconvection dSST and time-mean SST. A column-integrated moist static energy (MSE) budget analysis confirms the critical role of diurnal SST variability in the buildup of column MSE and the strength of MJO convection via stronger time-mean LH and diurnal moistening. Two complementary atmosphere-only simulations further elucidate the role of SST conditions in the predictive skill of MJO. The atmospheric model forced with the persistent initial SST, lacking enhanced preconvection warming and moistening, produces a weaker and delayed convection than the diurnally coupled run. The atmospheric model with prescribed daily-mean SST from the coupled run, while eliminating the delayed peak, continues to exhibit weaker convection due to the lack of strong moistening on a diurnal basis. The fact that time-evolving SST with a diurnal cycle strongly influences the onset and intensity of MJO convection is consistent with previous studies that identified an improved representation of diurnal SST as a potential source of MJO predictability.

scholarly journals Kelvin/Rossby Wave Partition of Madden-Julian Oscillation Circulations

Climate ◽  
2020 ◽  
Vol 9 (1) ◽  
pp. 2
Author(s):  
Patrick Haertel
Keyword(s):  
Rossby Wave ◽  
Large Scale ◽  
Atmospheric Model ◽  
Circulation System ◽  
System Of Equations ◽  
Wave Component ◽  
Madden Julian Oscillation ◽  
Kelvin Wave ◽  
Realistic View ◽  
State Of Rest

The Madden Julian Oscillation (MJO) is a large-scale convective and circulation system that propagates slowly eastward over the equatorial Indian and Western Pacific Oceans. Multiple, conflicting theories describe its growth and propagation, most involving equatorial Kelvin and/or Rossby waves. This study partitions MJO circulations into Kelvin and Rossby wave components for three sets of data: (1) a modeled linear response to an MJO-like heating; (2) a composite MJO based on atmospheric sounding data; and (3) a composite MJO based on data from a Lagrangian atmospheric model. The first dataset has a simple dynamical interpretation, the second provides a realistic view of MJO circulations, and the third occurs in a laboratory supporting controlled experiments. In all three of the datasets, the propagation of Kelvin waves is similar, suggesting that the dynamics of Kelvin wave circulations in the MJO can be captured by a system of equations linearized about a basic state of rest. In contrast, the Rossby wave component of the observed MJO’s circulation differs substantially from that in our linear model, with Rossby gyres moving eastward along with the heating and migrating poleward relative to their linear counterparts. These results support the use of a system of equations linearized about a basic state of rest for the Kelvin wave component of MJO circulation, but they question its use for the Rossby wave component.

scholarly journals Climatological Increased Precipitation from July to August in the Western North Pacific Region Simulated by CMIP6 Models

Atmosphere ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 664
Author(s):  
Xiao Dong ◽  
Renping Lin
Keyword(s):  
North Pacific ◽  
Western North Pacific ◽  
Vertical Motion ◽  
Atmospheric Model ◽  
Coupled Models ◽  
Model Simulations ◽  
Observational Analysis ◽  
Budget Analysis ◽  
Circulation Change ◽  
Precipitation Increase

In this study, the climatological precipitation increase from July to August over the western North Pacific (WNP) region was investigated through observations and simulations in the Coupled Model Intercomparison Project Phase 6 (CMIP6), atmospheric model simulations and historical experiments. Firstly, observational analysis showed that the precipitation increase is associated with a decrease in the local sea surface temperature (SST), indicating that the precipitation increase is not driven by the change in SST. In addition, the pattern of precipitation increase is similar to the vertical motion change at 500-hPa, suggesting that the precipitation increase is related to the circulation change. Moisture budget analysis further confirmed this relation. In addition to the observational analysis, the outputs from 26 CMIP6 models were further evaluated. Compared with atmospheric model simulations, air–sea coupled models largely improve the simulation of the climatological precipitation increase from July to August. Furthermore, model simulations confirmed that the bias in the precipitation increase is intimately associated with the circulation change bias. Thus, two factors are responsible for the bias of the precipitation increase from July to August in climate models: air–sea coupling processes and the performance in vertical motion change.

scholarly journals Storm Track Response to Oceanic Eddies in Idealized Atmospheric Simulations

2018 ◽  
Vol 32 (2) ◽  
pp. 445-463 ◽  
Author(s):  
A. Foussard ◽  
G. Lapeyre ◽  
R. Plougonven
Keyword(s):  
Large Scale ◽  
Heat Budget ◽  
Storm Track ◽  
Convective Heating ◽  
Western Boundary ◽  
Boundary Currents ◽  
Oceanic Fronts ◽  
Budget Analysis ◽  
Poleward Shift ◽  
Oceanic Eddies

ABSTRACT Large-scale oceanic fronts, such as in western boundary currents, have been shown to play an important role in the dynamics of atmospheric storm tracks. Little is known about the influence of mesoscale oceanic eddies on the free troposphere, although their imprint on the atmospheric boundary layer is well documented. The present study investigates the response of the tropospheric storm track to the presence of sea surface temperature (SST) anomalies associated with an eddying ocean. Idealized experiments are carried out in a configuration of a zonally reentrant channel representing the midlatitudes. The SST field is composed of a large-scale zonally symmetric front to which are added mesoscale eddies localized close to the front. Numerical simulations show a robust signal of a poleward shift of the storm track and of the tropospheric eddy-driven jet when oceanic eddies are taken into account. This is accompanied by more intense air–sea fluxes and convective heating above oceanic eddies. Also, a mean heating of the troposphere occurs poleward of the oceanic eddying region, within the storm track. A heat budget analysis shows that it is caused by a stronger diabatic heating within storms associated with more water advected poleward. This additional heating affects the baroclinicity of the flow, which pushes the jet and the storm track poleward.

scholarly journals A numerical study of the early stages of a tropical cyclogenesis in relation to the MJO

2015 ◽  
Vol 3 (8) ◽  
pp. 4919-4935
Author(s):  
J. Guerbette ◽  
M. Plu ◽  
C. Barthe ◽  
J.-F. Mahfouf
Keyword(s):  
Numerical Study ◽  
Active Phase ◽  
Atmospheric Model ◽  
Tropical Cyclogenesis ◽  
Limited Area ◽  
Madden Julian Oscillation ◽  
Low Level ◽  
Convective Systems ◽  
South West Indian Ocean ◽  
Low Level Jet

Abstract. The role of an active phase of the Madden–Julian Oscillation (MJO) on the evolution of a mesoscale convective systems (MCS) leading to a tropical depression is investigated in the South-West Indian Ocean during the Dynamics of the Madden–Julian Oscillation (DYNAMO) field experiment, with a numerical limited-area atmospheric model. A mesoscale vortex is followed in the low-troposphere from the initiation of the active MJO phase. It is shown that the interaction of the vortex with the Equatorial jet associated with the MJO plays an important role on the vortex development. As the vortex encounters the southern part of the low-level jet, it undergoes intensification that is explained by the barotropic conversion of kinetic energy from the low-level jet to the vortex.

Time–Space Characteristics of Diurnal Rainfall over Borneo and Surrounding Oceans as Observed by TRMM-PR

2006 ◽  
Vol 19 (7) ◽  
pp. 1238-1260 ◽  
Author(s):  
Hiroki Ichikawa ◽  
Tetsuzo Yasunari
Keyword(s):  
Diurnal Cycle ◽  
Large Scale ◽  
Intraseasonal Variability ◽  
Phase Speed ◽  
Tropical Rainfall Measuring Mission ◽  
Heavy Precipitation ◽  
Circulation Pattern ◽  
Leeward Side ◽  
Convective Rainfall ◽  
Time Space

Abstract Five years of Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) data were used to investigate the time and space characteristics of the diurnal cycle of rainfall over and around Borneo, an island in the Maritime Continent. The diurnal cycle shows a systematic modulation that is associated with intraseasonal variability in the large-scale circulation pattern, with regimes associated with low-level easterlies or westerlies over the island. The lower-tropospheric westerly (easterly) components correspond to periods of active (inactive) convection over the island that are associated with the passage of intraseasonal atmospheric disturbances related to the Madden–Julian oscillation. A striking feature is that rainfall activity propagates to the leeward side of the island between midnight and morning. The inferred phase speed of the propagation is about 3 m s−1 in the easterly regime and 7 m s−1 in the westerly regime. Propagation occurs over the entire island, causing a leeward enhancement of rainfall. The vertical structure of the developed convection/rainfall system differs remarkably between the two regimes. In the easterly regime, stratiform rains are widespread over the island at midnight, whereas in the westerly regime, local convective rainfall dominates. Over offshore regions, convective rainfall initially dominates then gradually decreases in both regimes, while the storms develop into deeper convective systems in the easterly regime. Aside from leeward rainfall propagation, shallow storms develop over the South China Sea region during the westerly regime, resulting in heavy precipitation from midnight through morning.

scholarly journals Coupled Land–Atmosphere Intraseasonal Variability of the West African Monsoon in a GCM

2010 ◽  
Vol 23 (21) ◽  
pp. 5557-5571 ◽  
Author(s):  
Sally L. Lavender ◽  
Christopher M. Taylor ◽  
Adrian J. Matthews
Keyword(s):  
Soil Moisture ◽  
Sensible Heat Flux ◽  
Intraseasonal Variability ◽  
West African Monsoon ◽  
Atmospheric Model ◽  
West African ◽  
The West ◽  
African Monsoon ◽  
Surface Sensible Heat Flux ◽  
Fully Coupled

Abstract Recent observational studies have suggested a role for soil moisture and land–atmosphere coupling in the 15-day westward-propagating mode of intraseasonal variability in the West African monsoon. This hypothesis is investigated with a set of three atmospheric general circulation model experiments. 1) When soil moisture is fully coupled with the atmospheric model, the 15-day mode of land–atmosphere variability is clearly identified. Precipitation anomalies lead soil moisture anomalies by 1–2 days, similar to the results from satellite observations. 2) To assess whether soil moisture is merely a passive response to the precipitation, or an active participant in this mode, the atmospheric model is forced with a 15-day westward-propagating cycle of regional soil moisture anomalies based on the fully coupled mode. Through a reduced surface sensible heat flux, the imposed wet soil anomalies induce negative low-level temperature anomalies and increased pressure (a cool high). An anticyclonic circulation then develops around the region of wet soil, enhancing northward moisture advection and precipitation to the west. Hence, in a coupled framework, this soil moisture–forced precipitation response would provide a self-consistent positive feedback on the westward-propagating soil moisture anomaly and implies an active role for soil moisture. 3) In a final sensitivity experiment, soil moisture is again externally prescribed but with all intraseasonal fluctuations suppressed. In the absence of soil moisture variability there are still pronounced surface sensible heat flux variations, likely due to cloud changes, and the 15-day westward-propagating precipitation signal is still present. However, it is not as coherent as in the previous experiments when interaction with soil moisture was permitted. Further examination of the soil moisture forcing experiment in GCM experiment 2 shows that this precipitation mode becomes phase locked to the imposed soil moisture anomalies. Hence, the 15-day westward-propagating mode in the West African monsoon can exist independently of soil moisture; however, soil moisture and land–atmosphere coupling act to feed back on the atmosphere and further enhance and organize it.

scholarly journals Prospects for Erratic and Intensifying Madden-Julian Oscillations

Climate ◽  
2020 ◽  
Vol 8 (2) ◽  
pp. 24
Author(s):  
Patrick Haertel
Keyword(s):  
Water Vapor ◽  
Tropical Cyclones ◽  
Radiative Forcing ◽  
Coupled Model ◽  
Equatorial Indian Ocean ◽  
Madden Julian Oscillation ◽  
Kelvin Wave ◽  
Late 20Th Century ◽  
Planetary Scale ◽  
One Year

The Madden–Julian Oscillation (MJO) is a planetary-scale convective disturbance that typically forms in the equatorial Indian Ocean, propagates slowly eastward, and dissipates near the date line. This study examines how the MJO changes in response to a changing radiative forcing in a fully-Lagrangian coupled model (LCM) that is shown to simulate robust and realistic MJOs. After the LCM is spun up for 160 years to reproduce the late 20th century climate, non-water-vapor longwave optical depth is increased over 70 years to model the effects of increasing concentrations of greenhouse gases. The model is then run for another 30 years without additional changes to the radiative forcing. After the radiative forcing is modified, the MJO generally becomes more frequent and intense, but it is also more variable from one year to the next. Not only do composite MJO rainfall perturbations increase, but wind, temperature, and moisture perturbations also become stronger. The aspect of the MJO’s structure that changes the most is the largely dry equatorial Kelvin wave circulation that circumnavigates the globe between moist phases of the MJO. Potential impacts of these changes included alterations to the way in which the MJO modulates tropical cyclones, monsoon disturbances, and El Niño.

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