scholarly journals WISHE‐Moisture Mode in a Vertically Resolved Model

2020 ◽  
Vol 12 (2) ◽  
Author(s):  
Željka Fuchs‐Stone
Keyword(s):  
Moisture Mode

TEMPERATURE-MOISTURE MODE OF THE MODERN BROWNER AT LOW AIR TEMPERATURES

2019 ◽  
Vol 10 (4) ◽  
Author(s):  
M. Zakharenko ◽  
◽  
V. Olynyk ◽  
V. Polyakovsky ◽  
V. Solomon ◽  
...  
Keyword(s):  
Air Temperatures ◽  
Moisture Mode

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 Changes in the MJO under Greenhouse Gas–Induced Warming in CMIP5 Models

2019 ◽  
Vol 32 (3) ◽  
pp. 803-821 ◽  
Author(s):  
Stephanie S. Rushley ◽  
Daehyun Kim ◽  
Ángel F. Adames
Keyword(s):  
Greenhouse Gas ◽  
Spectral Power ◽  
Phase Speed ◽  
Coupled Model ◽  
Similar Rate ◽  
Cmip5 Models ◽  
Zonal Scale ◽  
Adjustment Time ◽  
Zonal Wavenumber ◽  
Moisture Mode

This study investigates changes to the Madden–Julian oscillation (MJO) in response to greenhouse gas–induced warming during the twenty-first century. Changes in the MJO’s amplitude, phase speed, and zonal scale are examined in five models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) that demonstrate superior MJO characteristics. Under warming, the CMIP5 models exhibit a robust increase in the spectral power of planetary-scale, intraseasonal, eastward-propagating (MJO) precipitation anomalies (~10.9% K−1). The amplification of MJO variability is accompanied by an increase of the spectral power of the corresponding westward-traveling waves at a similar rate. This suggests that enhanced MJO variability in a warmer climate is likely caused by enhanced background tropical precipitation variability, not by changes in the MJO’s stability. All models examined show an increase in the MJO’s phase speed (1.8% K–1–4.5% K−1) and a decrease in the MJO’s zonal wavenumber (1.0% K–1–3.8% K−1). Using a linear moisture mode framework, this study tests the theory-predicted phase speed changes against the simulated phase speed changes. It is found that the MJO’s acceleration in a warmer climate is a result of enhanced horizontal moisture advection by the steepening of the mean meridional moisture gradient and the decrease in zonal wavenumber, which is partially offset by the lengthening of the convective moisture adjustment time scale and the increase in gross dry stability. While the ability of the linear moisture mode framework to explain MJO phase speed changes is model dependent, the theory can accurately predict the phase speed changes in the model ensemble.

scholarly journals Gross Moist Stability Analysis: Assessment of Satellite-Based Products in the GMS Plane

2017 ◽  
Vol 74 (6) ◽  
pp. 1819-1837 ◽  
Author(s):  
Kuniaki Inoue ◽  
Larissa E. Back
Keyword(s):  
Life Cycle ◽  
Phase Plane ◽  
Critical Line ◽  
Time Dependent ◽  
Moist Static Energy ◽  
Geographic Variations ◽  
Moisture Mode ◽  
Gross Moist Stability ◽  
Static Energy ◽  
Diagnostic Applications

Abstract New diagnostic applications of the gross moist stability (GMS) are proposed with demonstrations using satellite-based data. The plane of the divergence of column moist static energy (MSE) against the divergence of column dry static energy (DSE), referred to as the GMS plane here, is utilized. In this plane, one can determine whether the convection is in the amplifying phase or in the decaying phase; if a data point lies below (above) a critical line in the GMS plane, the convection is in the amplifying (decaying) phase. The GMS plane behaves as a phase plane in which each convective life cycle can be viewed as an orbiting fluctuation around the critical line, and this property is robust even on the MJO time scale. This phase-plane behavior indicates that values of the GMS can qualitatively predict the subsequent convective evolution. This study demonstrates that GMS analyses possess two different aspects: time-dependent and quasi-time-independent aspects. Transitions of time-dependent GMS can be visualized in the GMS plane as an orbiting fluctuation around the quasi-time-independent GMS line. The time-dependent GMS must be interpreted differently from the quasi-time-independent one, and the latter is the GMS relevant to moisture-mode theories. The authors listed different calculations of the quasi-time-independent GMS: (i) as a regression slope from a scatterplot and (ii) as a climatological quantity, which is the ratio of climatological MSE divergence to climatological DSE divergence. It is revealed that the latter, climatological GMS, is less appropriate as a diagnostic tool. Geographic variations in the quasi-time-independent GMS are plotted.

Moisture Modes and the Madden–Julian Oscillation

2009 ◽  
Vol 22 (11) ◽  
pp. 3031-3046 ◽  
Author(s):  
David J. Raymond ◽  
Željka Fuchs
Keyword(s):  
Large Scale ◽  
Strong Dependence ◽  
Final Analysis ◽  
Precipitable Water ◽  
Madden Julian Oscillation ◽  
Kelvin Wave ◽  
Mode Instability ◽  
Forecast System ◽  
Entropy Transport ◽  
Moisture Mode

Abstract Moisture mode instability is thought to occur in the tropical oceanic atmosphere when precipitation is a strongly increasing function of saturation fraction (precipitable water divided by saturated precipitable water) and when convection acts to increase the saturation fraction. A highly simplified model of the interaction between convection and large-scale flows in the tropics suggests that there are two types of convectively coupled disturbances: the moisture mode instability described above and another unstable mode dependent on fluctuations in the convective inhibition. The latter is associated with rapidly moving disturbances such as the equatorially coupled Kelvin wave. A toy aquaplanet beta-plane model with realistic sea surface temperatures produces a robust Madden–Julian oscillation–like disturbance that resembles the observed phenomenon in many ways. Convection in this model exhibits a strong dependence of precipitation on saturation fraction and does indeed act to increase this parameter in situations of weak environmental ventilation of disturbances, thus satisfying the criteria for moisture mode instability. In contrast, NCEP’s closely related Global Forecast System (GFS) and Climate Forecast System (CFS) models do not produce a realistic MJO. Investigation of moist entropy transport in NCEP’s final analysis (FNL), the data assimilation system feeding the GFS, indicates that convection tends to decrease the saturation fraction in these models, precluding moisture mode instability in most circumstances. Thus, evidence from a variety of sources suggests that the MJO is driven at least in part by moisture mode instability.

scholarly journals Reexamining the MJO Moisture Mode Theories with Normalized Phase Evolutions

2020 ◽  
Vol 33 (19) ◽  
pp. 8523-8536
Author(s):  
Lu Wang ◽  
Tim Li
Keyword(s):  
Boundary Layer ◽  
Characteristic Length ◽  
Deep Convection ◽  
Phase Speed ◽  
Phase Evolution ◽  
Kelvin Wave ◽  
Mode Theory ◽  
Budget Analysis ◽  
Moisture Mode ◽  
Static Energy

AbstractA normalization method is applied to MJO-scale precipitation and column integrated moist static energy (MSE) anomalies to clearly illustrate the phase evolution of MJO. It is found that the MJO peak phases do not move smoothly, rather they jump from the original convective region to a new location to its east. Such a discontinuous phase evolution is related to the emerging and developing of new congestus convection to the east of the preexisting deep convection. While the characteristic length scale of the phase jump depends on a Kelvin wave response, the associated time scale represents the establishment of an unstable stratification in the front due to boundary layer moistening. The combined effect of the aforementioned characteristic length and time scales determines the observed slow eastward phase speed. Such a phase evolution characteristic seems to support the moisture mode theory of the second type that emphasizes the boundary layer moisture asymmetry, because the moisture mode theory of the first type, which emphasizes the moisture or MSE tendency asymmetry, might favor more “smooth” phase propagation. A longitudinal-location-dependent premoistening mechanism is found based on moisture budget analysis. For the MJO in the eastern Indian Ocean, the premoistening in front of the MJO convection arises from vertical advection, whereas for the MJO over the western Pacific Ocean, it is attributed to the surface evaporating process.

scholarly journals Causal Evidence that Rotational Moisture Advection is Critical to the Superparameterized Madden–Julian Oscillation

2014 ◽  
Vol 71 (2) ◽  
pp. 800-815 ◽  
Author(s):  
Michael S. Pritchard ◽  
Christopher S. Bretherton
Keyword(s):  
Control Parameter ◽  
Madden Julian Oscillation ◽  
Rotational Component ◽  
Global Models ◽  
Moisture Advection ◽  
Moisture Mode ◽  
Gross Moist Stability ◽  
Tropical Moisture ◽  
Lines Of Evidence ◽  
Opposite Response

Abstract The authors investigate the hypothesis that horizontal moisture advection is critical to the eastward propagation of the Madden–Julian oscillation (MJO). Consistent diagnostic evidence has been found in recent MJO-permitting global models viewed from the moisture-mode dynamical paradigm. To test this idea in a causal sense, tropical moisture advection by vorticity anomalies is artificially modulated in a superparameterized global model known to produce a realistic MJO signal. Boosting horizontal moisture advection by tropical vorticity anomalies accelerates and amplifies the simulated MJO in tandem with reduced environmental gross moist stability. Limiting rotational horizontal moisture advection shuts the MJO down. These sensitivities are robust in that they are nearly monotonic with respect to the control parameter and emerge despite basic-state sensitivities favoring the opposite response. Speedup confirms what several diagnostic lines of evidence already suggest—that anomalous moisture advection is fundamental to MJO propagation. The rotational component is shown to be especially critical. Amplification further suggests it may play a role in adiabatically maintaining the MJO.

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