scholarly journals Toward an Understanding of the Madden-Julian Oscillation: With a Mesoscale-Convection-Resolving Model of 0.2 Degree Grid

2011 ◽  
Vol 2011 ◽  
pp. 1-34 ◽  
Author(s):  
Masanori Yamasaki
Keyword(s):  
Numerical Experiments ◽  
Large Scale ◽  
Warm Pool ◽  
Necessary Condition ◽  
Convective System ◽  
Madden Julian Oscillation ◽  
Moist Convection ◽  
Mesoscale Convection ◽  
Wide Range ◽  
Sst Anomaly

This paper describes results from numerical experiments which have been performed as the author's first step toward a better understanding of the Madden-Julian oscillation (MJO). This study uses the author's mesoscale-convection-resolving model that was developed in the 1980s to improve parametrization schemes of moist convection. Results from numerical experiments by changing the SST anomaly in the warm pool area indicate that the period of the MJO does not monotonously change with increasing SST anomaly. Between the two extreme cases (no anomaly and strong anomaly), there is a regime in which the period varies in a wide range from 20 to 60 days. In the case of no warm pool, eastward-propagating Kelvin waves are dominant, whereas in the case of a strong warm pool, it produces a quasi-stationary convective system (with pronounced time variation). In a certain regime between the two extreme cases, convective activities with two different properties are strongly interacted, and the period of oscillations becomes complicated. The properties and behaviors of large-scale convective system (LCS), synoptic-scale convective system (SCS), mesoscale convective system (MCS), and mesoscale convection (MC), which constitute the hierarchical structure of the MJO, are also examined. It is also shown that cloud clusters, which constitute the SCS (such as super cloud cluster SCC), consist of a few MCS, and a new MCS forms to the west of the existing MCS. The northwesterly and southwesterly low-level flows contribute to this feature. In view of recent emphasis of the importance of the relative humidity above the boundary layer, it is shown that the model can simulate convective processes that moisten the atmosphere, and the importance of latent instability (positive CAPE), which is a necessary condition for the wave-CISK, is emphasized.

scholarly journals Toward an Understanding of Tropical Cyclone Formation with a Nonhydrostatic, Mesoscale-Convection-Resolving Model§

2013 ◽  
Vol 7 (1) ◽  
pp. 37-50
Author(s):  
Masanori Yamasaki
Keyword(s):  
Tropical Cyclone ◽  
Numerical Experiments ◽  
Vertical Shear ◽  
Initial Time ◽  
Convective System ◽  
Vortex Center ◽  
Moist Convection ◽  
Mesoscale Convection ◽  
Tropical Cyclone Formation ◽  
Convective Systems

This paper describes results from numerical experiments which have been made toward a better understanding of tropical cyclone formation. This study uses a nonhydrostatic version of the author’s mesoscale-convection-resolving model that was developed in the 1980s to improve paramerization schemes of moist convection. In this study the horizontal grid size is taken to be 20 km in an area of 6,000 km x 3,000 km, and a non-uniform coarse grid is used in two areas to its north and south. Results from two numerical experiments are presented; one (case 1) without any environmental flow, and the other (case 2) with an easterly flow without low-level vertical shear. Three circular buoyancy perturbations are placed in the west-east direction at the initial time. Convection is initiated in the imposed latently unstable (positive CAPE) area. In both cases, a vortex with a pressure low is formed, and two band-shaped convective systems are formed to the north and the south of the vortex center. The vortex and two convective systems are oriented in the westsouthwest – eastnortheast direction, and their horizontal scales are nearly 2,000 km. In case 1, the band-shaped convective system on the southern side is stronger, and winds are stronger just to its south. In contrast, in case 2, the northern convective system is stronger, and winds are stronger just to its north. Therefore, the distributions of the equivalent potential temperature in the boundary layer and latent instability (positive buoyancy of the rising air) are also quite different between cases 1 and 2. The TC formation processes in these different cases are discussed, with an emphasis on the importance of examining the time change of latent instability field.

scholarly journals Influence of the Stratospheric Quasi-Biennial Oscillation on the Madden–Julian Oscillation during Austral Summer

2017 ◽  
Vol 74 (4) ◽  
pp. 1105-1125 ◽  
Author(s):  
Eriko Nishimoto ◽  
Shigeo Yoden
Keyword(s):  
Large Scale ◽  
Statistical Significance ◽  
Austral Summer ◽  
Horizontal Wind ◽  
Convective System ◽  
Madden Julian Oscillation ◽  
Quasi Biennial Oscillation ◽  
Enso Events ◽  
Convective Region ◽  
Biennial Oscillation

Abstract Influence of the stratospheric quasi-biennial oscillation (QBO) on the Madden–Julian oscillation (MJO) and its statistical significance are examined for austral summer (DJF) in neutral ENSO events during 1979–2013. The amplitude of the OLR-based MJO index (OMI) is typically larger in the easterly phase of the QBO at 50 hPa (E-QBO phase) than in the westerly (W-QBO) phase. Daily composite analyses are performed by focusing on phase 4 of the OMI, when the active convective system is located over the eastern Indian Ocean through the Maritime Continent. The composite OLR anomaly shows a larger negative value and slower eastward propagation with a prolonged period of active convection in the E-QBO phase than in the W-QBO phase. Statistically significant differences of the MJO activities between the QBO phases also exist with dynamical consistency in the divergence of horizontal wind, the vertical wind, the moisture, the precipitation, and the 100-hPa temperature. A conditional sampling analysis is also performed by focusing on the most active convective region for each day, irrespective of the MJO amplitude and phase. Composite vertical profiles of the conditionally sampled data over the most active convective region reveal lower temperature and static stability around the tropopause in the E-QBO phase than in the W-QBO phase, which indicates more favorable conditions for developing deep convection. This feature is more prominent and extends into lower levels in the upper troposphere over the most active convective region than other tropical regions. Composite longitude–height sections show similar features of the large-scale convective system associated with the MJO, including a vertically propagating Kelvin response.

scholarly journals Filtering the Stochastic Skeleton Model for the Madden–Julian Oscillation

2016 ◽  
Vol 144 (2) ◽  
pp. 501-527 ◽  
Author(s):  
Nan Chen ◽  
Andrew J. Majda
Keyword(s):  
Large Scale ◽  
Warm Pool ◽  
Model Error ◽  
Small Scale ◽  
Fast Wave ◽  
Madden Julian Oscillation ◽  
Computationally Efficient ◽  
Skeleton Model ◽  
Spatially Extended ◽  
Novel Strategy

Abstract The filtering and prediction of the Madden–Julian oscillation (MJO) and relevant tropical waves is a contemporary issue with significant implications for extended range forecasting. This paper examines the process of filtering the stochastic skeleton model for the MJO with noisy partial observations. A nonlinear filter, which captures the inherent nonlinearity of the system, is developed and judicious model error is included. Despite its nonlinearity, the special structure of this filter allows closed analytical formulas for updating the posterior states and is thus computationally efficient. A novel strategy for adding nonlinear observational noise to the envelope of convective activity is designed to guarantee its nonnegative property. Systematic calibration based on a cheap single-column version of the stochastic skeleton model provides a practical guideline for choosing the parameters in the full spatially extended system. With these column-tuned parameters, the full filter has a high overall filtering skill for Rossby waves but fails to recover the small-scale fast-oscillating Kelvin and moisture modes. An effectively balanced reduced filter involving a simple fast-wave averaging strategy is then developed, which greatly improves the skill of filtering the moisture modes and other fast-oscillating modes and enhances the total computational efficiency. Both the full and the reduced filters succeed in filtering the MJO and other large-scale features with both homogeneous and warm pool cooling/moistening backgrounds. The large bias in filtering the solutions by running the perfect model with noisy forcing is due to the noise accumulation, which indicates the importance of including judicious model error in designing filters.

New Metrics to Quantify Spatial and Temporal Characteristics of Precipitation Using 20-years TRMM-GPM Data for Evaluating Climate Models

2020 ◽  
Author(s):  
Shuyi Chen ◽  
Brandon Kerns
Keyword(s):  
Large Scale ◽  
Climate Models ◽  
Satellite Observation ◽  
Warm Pool ◽  
Spatial Filter ◽  
Early Results ◽  
Wide Range ◽  
Need To Evaluate ◽  
Global And Local ◽  
Global Precipitation

<p>Precipitation is a highly complex, multiscale entity in the global weather and climate system. It is affected by both global and local circulations over a wide range of time scales from hours to weeks and beyond. It is also an important measure of the water and energy cycle in climate models. To better understand the physical processes controlling precipitation in climate models, we need to evaluate precipitation not only in in terms of its global climatological distribution but also multiscale variability in time and space.</p><p>This study presents a new set of metrics to quantify characteristics of global precipitation using 20-years the TRMM-GPM Multisatellite Precipitation Analysis (TMPA) data from June 1998 to May 2018 over the global tropics-midlatitudes (50°S – 50°N) with 3-hourly and 0.25-degree resolutions.  We developed a method to identify large-scale precipitation objects (LPOs) using a temporal-spatial filter and then track the LPOs in time, namely the Large-scale Precipitation Tracking systems (LPTs) as described in Kerns and Chen (2016, 2020, JGR-Atmos). The most unique feature of this method is that it can distinguish large-scale precipitation organized by, for example, monsoons and the Madden-Julian Oscillation (MJO), from that of mesoscale and synoptic scale weather systems, as well as those relatively stationary local topographically and diurnally forced precipitation. The new precipitation metrics based on the satellite observation are used to evaluate climate models.  Early results show that most models overproduce precipitation over land in non-LPTs and underestimate large-scale precipitation (LPTs) over the oceans compared with the observations. For example, the MJO contributes up to 40-50% of the observed annual precipitation over the Indio-Pacific warm pool region, which are usually much less in the models because of models’ inability to represent the MJO dynamics. Furthermore, the spatial variability of precipitation associated with ENSO is more pronounced in the observations than models.</p>

Coupled Modes of the Warm Pool Climate System. Part I: The Role of Air–Sea Interaction in Maintaining Madden–Julian Oscillation

1998 ◽  
Vol 11 (8) ◽  
pp. 2116-2135 ◽  
Author(s):  
Bin Wang ◽  
Xiaosu Xie
Keyword(s):  
Mixed Layer ◽  
Large Scale ◽  
Low Frequency ◽  
Warm Pool ◽  
Internal Dynamic ◽  
Cold Tongue ◽  
Madden Julian Oscillation ◽  
Ocean Mixed Layer ◽  
Coupled Modes ◽  
Coupled Mode

Abstract Over the warm pool of the equatorial Indian and western Pacific Oceans, both the climatological mean state and the processes of atmosphere–ocean interaction differ fundamentally from their counterparts over the cold tongue of the equatorial eastern Pacific. A model suitable for studying the coupled instability in both the warm pool and cold tongue regimes is advanced. The model emphasizes ocean mixed layer physics and thermodynamical coupling that are essential for the warm pool regime. Different coupled unstable modes are found under each regime. In contrast to the cold tongue basic state, which favors coupled unstable low-frequency SST mode, the warm pool regime (moderate mean surface westerlies and deep thermocline) is conducive for high-frequency (intraseasonal timescale) coupled unstable modes. The wind–mixed layer interaction through entrainment/evaporation plays a central role in the warm pool instability. The cloud-radiation feedback enhances the instability, whereas the ocean wave dynamics have little impact. The thermodynamic coupling between the atmosphere and ocean mixed layer results in a positive SST anomaly leading convection, which provides eddy available potential energy for growing coupled mode. The relatively slow mixed layer response to atmospheric forcing favors the growth of planetary-scale coupled modes. The presence of mean westerlies suppresses the low-frequency SST mode. The characteristics of the eastward-propagating coupled mode of the warm pool system compares favorably with the large-scale features of the observed Madden–Julian Oscillation (MJO). This suggests that, in addition to atmospheric internal dynamic instability, the ocean mixed layer thermodynamic processes interacting with the atmosphere may play an active part in sustaining the MJO by (a) destabilizing atmospheric moist Kelvin waves, (b) providing a longwave selection mechanism, and (c) slowing down phase propagation and setting up the 40–50-day timescale.

scholarly journals Parameterization of the Spatial Variability of Rain for Large-Scale Models and Remote Sensing

2015 ◽  
Vol 54 (10) ◽  
pp. 2027-2046 ◽  
Author(s):  
Z. J. Lebo ◽  
C. R. Williams ◽  
G. Feingold ◽  
V. E. Larson
Keyword(s):  
Spatial Variability ◽  
Large Scale ◽  
Rain Rate ◽  
Numerical Models ◽  
Spatial Scales ◽  
Warm Pool ◽  
Radar Data ◽  
Model Output ◽  
Wide Range ◽  
Averaged Model

AbstractThe spatial variability of rain rate R is evaluated by using both radar observations and cloud-resolving model output, focusing on the Tropical Warm Pool–International Cloud Experiment (TWP-ICE) period. In general, the model-predicted rain-rate probability distributions agree well with those estimated from the radar data across a wide range of spatial scales. The spatial variability in R, which is defined according to the standard deviation of R (for R greater than a predefined threshold Rmin) σ(R), is found to vary according to both the average of R over a given footprint μ(R) and the footprint size or averaging scale Δ. There is good agreement between area-averaged model output and radar data at a height of 2.5 km. The model output at the surface is used to construct a scale-dependent parameterization of σ(R) as a function of μ(R) and Δ that can be readily implemented into large-scale numerical models. The variability in both the rainwater mixing ratio qr and R as a function of height is also explored. From the statistical analysis, a scale- and height-dependent formulation for the spatial variability of both qr and R is provided for the analyzed tropical scenario. Last, it is shown how this parameterization can be used to assist in constraining parameters that are often used to describe the surface rain-rate distribution.

scholarly journals Moist Convection and the Thermal Stratification of the Extratropical Troposphere

2008 ◽  
Vol 65 (11) ◽  
pp. 3571-3583 ◽  
Author(s):  
Tapio Schneider ◽  
Paul A. O’Gorman
Keyword(s):  
Latent Heat ◽  
Thermal Stratification ◽  
General Circulation ◽  
Large Scale ◽  
Circulation Model ◽  
Lapse Rate ◽  
Moist Convection ◽  
Wide Range ◽  
Simulation Results ◽  
Warm Climates

Abstract Simulations with an aquaplanet general circulation model show that sensible and latent heat transport by large-scale eddies influences the extratropical thermal stratification over a wide range of climates, even in relatively warm climates with small meridional surface temperature gradients. Variations of the lapse rate toward which the parameterized moist convection in the model relaxes atmospheric temperature profiles demonstrate that the convective lapse rate only marginally affects the extratropical thermal stratification in Earth-like and colder climates. In warmer climates, the convective lapse rate does affect the extratropical thermal stratification, but the effect is still smaller than would be expected if moist convection alone controlled the thermal stratification. A theory for how large-scale eddies modify the thermal stratification of dry atmospheres is consistent with the simulation results for colder climates. For warmer and moister climates, however, theories and heuristics that have been proposed to account for the extratropical thermal stratification are not consistent with the simulation results. Theories for the extratropical thermal stratification will generally have to take transport of sensible and latent heat by large-scale eddies into account, but moist convection may only need to be taken into account regionally and in sufficiently warm climates.

scholarly journals The amplification of Madden-Julian Oscillation boosted by temperature feedback

2021 ◽  
Author(s):  
Guosen Chen
Keyword(s):  
Latent Heat ◽  
Large Scale ◽  
Theoretical Study ◽  
Interaction Model ◽  
Energy Generation ◽  
Warm Pool ◽  
Madden Julian Oscillation ◽  
Rotation Effect ◽  
Temperature Feedback ◽  
Temperature Tendency

AbstractDue to small Coriolis force in tropics, the theoretical study of Madden-Julian Oscillation (MJO) often assumes weak temperature gradient balance, which neglects the temperature feedback (manifested in temperature tendency term). In this study, the effect of the temperature feedback on the MJO is investigated by using the MJO trio-interaction model, which can capture the essential large-scale features of the MJO.The scale analysis indicates that the rotation effect is strong for the MJO scales, so that the temperature feedback is as import as the moisture feedback (manifested in moisture tendency term), the latter is often considered to be critical for MJO. The experiments with the theoretical model show that the temperature feedback has significant impact on the MJO’s maintenance. When the temperature feedback is turned off, the simulated MJO cannot be maintained over the warm pool. This is because the temperature feedback could boost the energy generation. Without temperature feedback, only the latent heat can be generated. With temperature feedback, not only the latent heat but also the enthalpy (and therefore the available potential energy) can be generated. Therefore, the total energy generation is more efficient with temperature feedback, favoring the self-maintenance of the MJO. Further investigation shows that this effect of the temperature feedback on MJO amplification can be inferred from observations.The findings here indicates that the temperature feedback could have non-negligible impacts on MJO, and have implications in the simulation of MJO.

scholarly journals Convection Modeling of Pure-steam Atmospheres

2021 ◽  
Vol 923 (1) ◽  
pp. L15
Author(s):  
Xianyu Tan ◽  
Maxence Lefèvre ◽  
Raymond T. Pierrehumbert
Keyword(s):  
Gravity Waves ◽  
Large Scale ◽  
Three Dimensional ◽  
Basic Structure ◽  
Model Parameters ◽  
Moist Convection ◽  
Wide Range ◽  
Convective Parameterization Scheme ◽  
Pure Steam ◽  
Convection Parameterization

Abstract Condensable species are crucial to shaping planetary climate. A wide range of planetary climate systems involve understanding nondilute condensable substances and their influence on climate dynamics. There has been progress on large-scale dynamical effects and on 1D convection parameterization, but resolved 3D moist convection remains unexplored in nondilute conditions, though it can have a profound impact on temperature/humidity profiles and cloud structure. In this work, we tackle this problem for pure-steam atmospheres using three-dimensional, high-resolution numerical simulations of convection in postrunaway atmospheres. We show that the atmosphere is composed of two characteristic regions, an upper condensing region dominated by gravity waves and a lower noncondensing region characterized by convective overturning cells. Velocities in the condensing region are much smaller than those in the lower, noncondensing region, and the horizontal temperature variation is small. Condensation in the thermal photosphere is largely driven by radiative cooling and tends to be statistically homogeneous. Some condensation also happens deeper, near the boundary of the condensing region, due to triggering by gravity waves and convective penetrations and exhibits random patchiness. This qualitative structure is insensitive to varying model parameters, but quantitative details may differ. Our results confirm theoretical expectations that atmospheres close to the pure-steam limit do not have organized deep convective plumes in the condensing region. The generalized convective parameterization scheme discussed in Ding & Pierrehumbert is appropriate for handling the basic structure of atmospheres near the pure-steam limit but cannot capture gravity waves and their mixing which appear in 3D convection-resolving models.

scholarly journals The Life Cycle of Anvil Clouds and the Top-of-Atmosphere Radiation Balance over the Tropical West Pacific

2018 ◽  
Vol 31 (24) ◽  
pp. 10059-10080 ◽  
Author(s):  
Casey J. Wall ◽  
Dennis L. Hartmann ◽  
Mandana M. Thieman ◽  
William L. Smith ◽  
Patrick Minnis
Keyword(s):  
Life Cycle ◽  
Large Scale ◽  
Warm Pool ◽  
Mesoscale Convective Systems ◽  
Radiation Balance ◽  
Convective Systems ◽  
Cloud Radiative Effect ◽  
Mesoscale Convective ◽  
Sst Anomaly ◽  
Cloud Radiative Effects

Observations from a geostationary satellite are used to study the life cycle of mesoscale convective systems (MCS), their associated anvil clouds, and their effects on the radiation balance over the warm pool of the tropical western Pacific Ocean. In their developing stages, MCS primarily consist of clouds that are optically thick and have a negative net cloud radiative effect (CRE). As MCS age, ice crystals in the anvil become larger, the cloud top lowers somewhat, and cloud radiative effects decrease in magnitude. Shading from anvils causes cool anomalies in the underlying sea surface temperature (SST) of up to −0.6°C. MCS often occur in clusters that are embedded within large westward-propagating disturbances, and therefore shading from anvils can cool SSTs over regions spanning hundreds of kilometers. Triggering of convection is more likely to follow a warm SST anomaly than a cold SST anomaly on a time scale of several days. This information is used to evaluate hypotheses for why, over the warm pool, the average shortwave and longwave CRE are individually large but nearly cancel. The results are consistent with the hypothesis that the cancellation in CRE is caused by feedbacks among cloud albedo, large-scale circulation, and SST.

Sign in / Sign up

Export Citation Format

Share Document