Assessing the role of air-sea coupling in predicting Madden-Julian Oscillation with an atmosphere-ocean coupled model

2021 ◽  
pp. 1-58
Author(s):  
Jiye Wu ◽  
Yue Li ◽  
Jing-Jia Luo ◽  
Xianan Jiang
Keyword(s):  
General Circulation ◽  
Global Climate ◽  
Critical Role ◽  
Circulation Model ◽  
General Circulation Models ◽  
Asymmetric Structure ◽  
Boreal Winter ◽  
Madden Julian Oscillation ◽  
Weather Extremes

AbstractThe Madden-Julian Oscillation (MJO) provides an important source of sub-seasonal to seasonal (S2S) predictability. Improved MJO prediction can be beneficial to S2S prediction of global climate and associated weather extremes. In this study, hindcasts based on an atmosphere-ocean coupled general circulation model (CGCM) are compared to those based on atmosphere general circulation models (AGCMs) to investigate influences of air-sea interactions on MJO prediction. Our results suggest that MJO prediction skill can be extended about one week longer in the CGCM hindcasts than AGCM-only experiments, particularly for boreal winter predictions.Further analysis suggests that improved MJO prediction in the CGCM is closely associated with improved representation of moistening processes. Compared to the AGCM experiments, the CGCM better predicts the boundary-layer moisture preconditioning to the east of MJO convection, which is generally considered crucial for triggering MJO deep convection. Meanwhile, the widely extended east-west asymmetric structure in free-tropospheric moisture tendency anomalies relative to the MJO convection center as seen in the observations is also well predicted in the CGCM. Improved prediction of MJO moisture processes in CGCM is closely associated with better representation of the zonal scale of MJO circulation and stronger Kelvin waves to the east of MJO convection, both of which have been recently suggested conductive for MJO eastward propagation. The above improvements by including air-sea coupling could be largely attributed to the realistic MJO-induced SST fluctuations through the convection-SST feedback. This study confirms a critical role of atmosphere-ocean coupling for the improvement of MJO prediction.

scholarly journals Role of Maritime Continent Land Convection on the Mean State and MJO Propagation

2020 ◽  
Vol 33 (5) ◽  
pp. 1659-1675 ◽  
Author(s):  
Min-Seop Ahn ◽  
Daehyun Kim ◽  
Yoo-Geun Ham ◽  
Sungsu Park
Keyword(s):  
Climate Model ◽  
Global Climate ◽  
Global Climate Model ◽  
Critical Role ◽  
Moisture Gradient ◽  
Moisture Distribution ◽  
Boreal Winter ◽  
Maritime Continent ◽  
The Mean

AbstractThe Maritime Continent (MC) region is known as a “barrier” in the life cycle of the Madden–Julian oscillation (MJO). During boreal winter, the MJO detours the equatorial MC land region southward and propagates through the oceanic region. Also, about half of the MJO events that initiate over the Indian Ocean cease around the MC. The mechanism through which the MC affects MJO propagation, however, has remained unanswered. The current study investigates the MJO–MC interaction with a particular focus on the role of MC land convection. Using a global climate model that simulates both mean climate and MJO realistically, we performed two sensitivity experiments in which updraft plume radius is set to its maximum and minimum value only in the MC land grid points, making convective top deeper and shallower, respectively. Our results show that MC land convection plays a key role in shaping the 3D climatological moisture distribution around the MC through its local and nonlocal effects. Shallower and weaker MC land convection results in a steepening of the vertical and meridional mean moisture gradient over the MC region. The opposite is the case when MC land convection becomes deeper and stronger. The MJO’s eastward propagation is enhanced (suppressed) with the steeper (lower) mean moisture gradient. The moist static energy (MSE) budget of the MJO reveals the vertical and meridional advection of the mean MSE by MJO wind anomalies as the key processes that are responsible for the changes in MJO propagation characteristics. Our results pinpoint the critical role of the background moisture gradient on MJO propagation.

scholarly journals The Response of the Midlatitude Jet to Regional Polar Heating in a Simple Storm-Track Model

2019 ◽  
Vol 32 (10) ◽  
pp. 2869-2885
Author(s):  
Paolo Ruggieri ◽  
Fred Kucharski ◽  
Lenka Novak
Keyword(s):  
General Circulation ◽  
State Of The Art ◽  
Global Climate ◽  
Storm Track ◽  
Circulation Model ◽  
General Circulation Models ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Strong Response ◽  
Arctic Sea

Abstract Given the recent changes in the Arctic sea ice, understanding the effects of the resultant polar warming on the global climate is of great importance. However, the interaction between the Arctic and midlatitude circulation involves a complex chain of mechanisms, which leaves state-of-the-art general circulation models unable to represent this interaction unambiguously. This study uses an idealized general circulation model to provide a process-based understanding of the sensitivity of the midlatitude circulation to the location of high-latitude warming. A simplified atmosphere is simulated with a single zonally localized midlatitude storm track, which is analogous to the storm tracks in the Northern Hemisphere. It is found that even small changes in the position of the forcing relative to that storm track can lead to very different responses in the midlatitude circulation. More specifically, it is found that heating concentrated in one region may cause a substantially stronger global response compared to when the same amount of heating is distributed across all longitudes at the same latitude. Linear interference between climatological and anomalous flow is an important component of the response, but it does not explain differences between different longitudes of the forcing. Feedbacks from atmospheric transient eddies are found to be associated with this strong response. A dependence between the climatological jet latitude and the jet response to polar surface heating is found. These results can be used to design and interpret experiments with complex state-of-the-art models targeted at Arctic–midlatitude interactions.

Investigating quasi-resonant Rossby waves with an idealized general circulation model

2020 ◽  
Author(s):  
Todd Mooring ◽  
Marianna Linz
Keyword(s):  
General Circulation Model ◽  
General Circulation ◽  
Rossby Waves ◽  
Circulation Model ◽  
General Circulation Models ◽  
Weather Extremes ◽  
Dynamical Mechanism ◽  
Atmospheric Physics ◽  
Coupled General Circulation Models ◽  
Mean State

<p>Petoukhov et al.’s (2013, PNAS) hypothesis of quasi-resonant Rossby waves as a mechanism for destructive weather extremes—both heat- and rain-related, observed and projected—has received a great deal of attention in recent years.  Most notably, it has been used for diagnostic studies of reanalysis products and full-physics atmospheric or coupled general circulation models. However, studies of this sort essentially assume (rather than test) the validity of the underlying theory.</p><p>Since the quasi-resonance theoretical arguments do not explicitly involve the full complexity of atmospheric physics, it ought to be possible to test them within the much simpler framework of an idealized general circulation model. By carefully constructing the forcing fields for such a model, we will achieve control of its zonal mean state and thus the waveguide properties of the zonal jet. We will explore the properties of the quasi-stationary Rossby waves in such simulations to test whether they have the properties predicted by Petoukhov et al. By testing this dynamical mechanism in a simplified model, we can better understand its applicability and limitations for investigations of future climate.</p>

The Role of the Central Asian Mountains on the Midwinter Suppression of North Pacific Storminess

2010 ◽  
Vol 67 (11) ◽  
pp. 3706-3720 ◽  
Author(s):  
Hyo-Seok Park ◽  
John C. H. Chiang ◽  
Seok-Woo Son
Keyword(s):  
Energy Conversion ◽  
North Pacific ◽  
General Circulation ◽  
Wave Packets ◽  
Circulation Model ◽  
Boreal Winter ◽  
Stationary Waves ◽  
Central Asian ◽  
Baroclinic Energy Conversion

Abstract The role of the central Asian mountains on North Pacific storminess is examined using an atmospheric general circulation model by varying the height and the areas of the mountains. A series of model integrations show that the presence of the central Asian mountains suppresses the North Pacific storminess by 20%–30% during boreal winter. Their impact on storminess is found to be small during other seasons. The mountains amplify stationary waves and effectively weaken the high-frequency transient eddy kinetic energy in boreal winter. Two main causes of the reduced storminess are diagnosed. First, the decrease in storminess appears to be associated with a weakening of downstream eddy development. The mountains disorganize the zonal coherency of wave packets and refract them more equatorward. As the zonal traveling distance of wave packets gets substantially shorter, downstream eddy development gets weaker. Second, the central Asian mountains suppress the global baroclinic energy conversion. The decreased baroclinic energy conversion, particularly over the eastern Eurasian continent, decreases the number of eddy disturbances entering into the western North Pacific. The “barotropic governor” does not appear to explain the reduced storminess in our model simulations.

Downscaling general circulation model output: a review of methods and limitations

1997 ◽  
Vol 21 (4) ◽  
pp. 530-548 ◽  
Author(s):  
R.L. Wilby ◽  
T.M.L. Wigley
Keyword(s):  
General Circulation ◽  
Climate Models ◽  
Daily Precipitation ◽  
Global Climate ◽  
Circulation Model ◽  
General Circulation Models ◽  
Limited Area ◽  
Regression Methods ◽  
Present Generation ◽  
Precipitation Characteristics

General circulation models (GCMs) suggest that rising concentrations of greenhouse gases may have significant consequences for the global climate. What is less clear is the extent to which local (subgrid) scale meteorological processes will be affected. So-called 'downscaling' techniques have subsequently emerged as a means of bridging the gap between what climate modellers are currently able to provide and what impact assessors require. This article reviews the present generation of downscaling tools under four main headings: regression methods; weather pattern (circulation)-based approaches; stochastic weather generators; and limited-area climate models. The penultimate section summarizes the results of an international experiment to intercompare several precipitation models used for downscaling. It shows that circulation-based downscaling methods perform well in simulating present observed and model-generated daily precipitation characteristics, but are able to capture only part of the daily precipitation variability changes associated with model-derived changes in climate. The final section examines a number of ongoing challenges to the future development of climate downscaling.

scholarly journals A Unified Moisture Mode Framework for Seasonality of the Madden–Julian Oscillation

2018 ◽  
Vol 31 (11) ◽  
pp. 4215-4224 ◽  
Author(s):  
Xianan Jiang ◽  
Ángel F. Adames ◽  
Ming Zhao ◽  
Duane Waliser ◽  
Eric Maloney
Keyword(s):  
Close Association ◽  
Critical Role ◽  
Boreal Winter ◽  
Madden Julian Oscillation ◽  
Equatorial Wave ◽  
Moisture Mode ◽  
Northward Propagation ◽  
The Mean ◽  
Moisture Pattern

The Madden–Julian oscillation (MJO) exhibits pronounced seasonality. While it is largely characterized by equatorially eastward propagation during the boreal winter, MJO convection undergoes marked poleward movement over the Asian monsoon region during summer, producing a significant modulation of monsoon rainfall. In classical MJO theories that seek to interpret the distinct seasonality in MJO propagation features, the role of equatorial wave dynamics has been emphasized for its eastward propagation, whereas coupling between MJO convection and the mean monsoon flow is considered essential for its northward propagation. In this study, a unified physical framework based on the moisture mode theory, is offered to explain the seasonality in MJO propagation. Moistening and drying caused by horizontal advection of the lower-tropospheric mean moisture by MJO winds, which was recently found to be critical for the eastward propagation of the winter MJO, is also shown to play a dominant role in operating the northward propagation of the summer MJO. The seasonal variations in the mean moisture pattern largely shape the distinct MJO propagation in different seasons. The critical role of the seasonally varying climatological distribution of moisture for the MJO propagation is further supported by the close association between model skill in representing the MJO propagation and skill at producing the lower-tropospheric mean moisture pattern. This study thus pinpoints an important direction for climate model development for improved MJO representation during all seasons.

scholarly journals Effects of Surface Orography and Land–Sea Contrast on the Madden–Julian Oscillation in the Maritime Continent: A Numerical Study Using ECHAM5-SIT

2017 ◽  
Vol 30 (23) ◽  
pp. 9725-9741 ◽  
Author(s):  
Wan-Ling Tseng ◽  
Huang-Hsiung Hsu ◽  
Noel Keenlyside ◽  
Chiung-Wen June Chang ◽  
Ben-Jei Tsuang ◽  
...  
Keyword(s):  
General Circulation ◽  
Numerical Study ◽  
Empirical Studies ◽  
Circulation Model ◽  
Wave Structure ◽  
Boreal Winter ◽  
Madden Julian Oscillation ◽  
Maritime Continent ◽  
Zonal Scale ◽  
Accurate Forecast

This study uses the atmospheric general circulation model (AGCM) ECHAM5 coupled with the newly developed Snow–Ice–Thermocline model (ECHAM5-SIT) to examine the effects of orography and land–sea contrast on the Madden–Julian oscillation (MJO) in the Maritime Continent (MC) during boreal winter. The ECHAM5-SIT is one of the few AGCMs that realistically simulate the major characteristics of the MJO. Three experiments are conducted with realistic topography, without orography, and with oceans only in the MC region to evaluate the relative effects of orography and land–sea contrast. Orography and land–sea contrast have the following effects on the MJO in the MC: 1) a larger amplitude, 2) a smaller zonal scale, 3) more realistic periodicity and stronger eastward-propagating signals, 4) a stronger southward detour during the eastward propagation, 5) a distorted coupled Kelvin–Rossby wave structure, and 6) larger low-level moisture convergence. The existence of mountainous islands also enhances the mean westerly in the eastern Indian Ocean and the western MC, as well as the moisture content over the MC. This enhancement of mean states contributes to the stronger eastward-propagating MJO. The findings herein suggest that theoretical and empirical studies, which are largely derived from an aquaplanet framework, have likely provided an oversimplified view of the MJO. The effects of mountainous islands should be considered for better understanding and more accurate forecast of the MJO.

scholarly journals Optimal Initial Perturbations for Ensemble Prediction of the Madden–Julian Oscillation during Boreal Winter

2012 ◽  
Vol 25 (14) ◽  
pp. 4932-4945 ◽  
Author(s):  
Yoo-Geun Ham ◽  
Siegfried Schubert ◽  
Yehui Chang
Keyword(s):  
Zonal Wind ◽  
General Circulation ◽  
Winter Season ◽  
Circulation Model ◽  
Ensemble Prediction ◽  
Boreal Winter ◽  
Random Perturbations ◽  
Madden Julian Oscillation ◽  
Bivariate Correlation ◽  
Forecast Lead Time

Abstract An initialization strategy, tailored to the prediction of the Madden–Julian oscillation (MJO), is evaluated using the Goddard Earth Observing System Model, version 5 (GEOS-5), coupled general circulation model (CGCM). The approach is based on the empirical singular vectors (ESVs) of a reduced-space statistically determined linear approximation of the full nonlinear CGCM. The initial ESV, extracted using 10 years (1990–99) of boreal winter hindcast data, has zonal wind anomalies over the western Indian Ocean, while the final ESV (at a forecast lead time of 10 days) reflects a propagation of the zonal wind anomalies to the east over the Maritime Continent—an evolution that is characteristic of the MJO. A new set of ensemble hindcasts are produced for the boreal winter season from 1990 to 1999 in which the leading ESV provides the initial perturbations. The results are compared with those from a set of control hindcasts generated using random perturbations. It is shown that the ESV-based predictions have a systematically higher bivariate correlation skill in predicting the MJO compared to those using the random perturbations. Furthermore, the improvement in the skill depends on the phase of the MJO. The ESV is particularly effective in increasing the forecast skill during those phases of the MJO in which the control has low skill (with correlations increasing by as much as 0.2 at 20–25-day lead times), as well as during those times in which the MJO is weak.

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