Differences between More Divergent and More Rotational Types of Convectively Coupled Equatorial Waves. Part II: Composite Analysis based on Space–Time Filtering

2012 ◽  
Vol 69 (1) ◽  
pp. 17-34 ◽  
Author(s):  
Kazuaki Yasunaga ◽  
Brian Mapes
Keyword(s):  
Water Vapor ◽  
Level Density ◽  
Space Time ◽  
Mesoscale Convective Systems ◽  
Equatorial Waves ◽  
Stratiform Rain ◽  
Convective Systems ◽  
Convectively Coupled Equatorial Waves ◽  
Mesoscale Convective ◽  
Rotational Waves

Abstract This paper describes an analysis of multiyear satellite datasets to characterize the modulations of convective versus stratiform rain, rain system size, and column water vapor by convectively coupled equatorial waves. Composites are built around space–time filtered equatorial-belt data from the Tropical Rainfall Measuring Mission (TRMM) 3B42 rainfall product, while TRMM Precipitation Radar (PR) and passive microwave data are the composited variables. The results are consistent with the more reanalysis-dependent findings in Part I, indicating that higher-frequency (or more divergent) waves, such as Kelvin and inertia–gravity families, modulate mesoscale convective systems and stratiform rain relatively more, whereas slower (or more rotational) types such as Rossby, mixed Rossby–gravity, and tropical depression (TD) or “easterly” waves primarily modulate convective rain and smaller-sized precipitation systems. Column water vapor composites indicate that the more rotational wave types modulate the moisture field more pronouncedly than do the divergent waves, leading the authors to speculate that the slow/rotational versus fast/wavelike distinction in precipitation characteristics may correspond to the different balances of two main convective coupling mechanisms: moisture control of cumulus cells versus convective inhibition control (via low-level density waves) of mesoscale convective systems. The Madden–Julian oscillation (MJO) is unique in that it exhibits prominent modulation of both stratiform precipitation (like the fast divergent waves) and small-sized precipitation features, convective rainfall, and moisture (like the other low-frequency, rotational waves). A composite of other waves’ amplitudes as a function of MJO amplitude and phase shows that divergent waves are more active in the developing phase and rotational waves are more active in the decaying rather than developing phase of the MJO.

scholarly journals Models for Multiscale Interactions. Part II: Madden–Julian Oscillation, Moisture, and Convective Momentum Transport

2016 ◽  
Vol 56 ◽  
pp. 10.1-10.5 ◽  
Author(s):  
Andrew J. Majda ◽  
Samuel N. Stechmann
Keyword(s):  
Tropical Cyclones ◽  
Momentum Transport ◽  
Mesoscale Convective Systems ◽  
Equatorial Waves ◽  
Madden Julian Oscillation ◽  
Synoptic Scale ◽  
Convective Systems ◽  
Convectively Coupled Equatorial Waves ◽  
Mesoscale Convective ◽  
Convective Momentum Transport

Abstract It is well known that the envelope of the Madden–Julian oscillation (MJO) consists of smaller-scale convective systems, including mesoscale convective systems (MCS), tropical cyclones, and synoptic-scale waves called “convectively coupled equatorial waves” (CCW). In fact, recent results suggest that the fundamental mechanisms of the MJO involve interactions between the synoptic-scale CCW and their larger-scale environment (Majda and Stechmann). In light of this, this chapter reviews recent and past work on two-way interactions between convective systems—both MCSs and CCW—and their larger-scale environment, with a particular focus given to recent work on MJO–CCW interactions.

scholarly journals Near-Surface Thermodynamic Sensitivities in Simulated Extreme-Rain-Producing Mesoscale Convective Systems

2017 ◽  
Vol 145 (6) ◽  
pp. 2177-2200 ◽  
Author(s):  
Russ S. Schumacher ◽  
John M. Peters
Keyword(s):  
Water Vapor ◽  
Initial Conditions ◽  
Weather Prediction ◽  
Mesoscale Convective Systems ◽  
Cold Pool ◽  
Near Surface ◽  
Low Level ◽  
Convective Systems ◽  
Mesoscale Convective ◽  
Outflow Boundary

Abstract This study investigates the influences of low-level atmospheric water vapor on the precipitation produced by simulated warm-season midlatitude mesoscale convective systems (MCSs). In a series of semi-idealized numerical model experiments using initial conditions gleaned from composite environments from observed cases, small increases in moisture were applied to the model initial conditions over a layer either 600 m or 1 km deep. The precipitation produced by the MCS increased with larger moisture perturbations as expected, but the rainfall changes were disproportionate to the magnitude of the moisture perturbations. The experiment with the largest perturbation had a water vapor mixing ratio increase of approximately 2 g kg−1 over the lowest 1 km, corresponding to a 3.4% increase in vertically integrated water vapor, and the area-integrated MCS precipitation in this experiment increased by nearly 60% over the control. The locations of the heaviest rainfall also changed in response to differences in the strength and depth of the convectively generated cold pool. The MCSs in environments with larger initial moisture perturbations developed stronger cold pools, and the convection remained close to the outflow boundary, whereas the convective line was displaced farther behind the outflow boundary in the control and the simulations with smaller moisture perturbations. The high sensitivity of both the amount and location of MCS rainfall to small changes in low-level moisture demonstrates how small moisture errors in numerical weather prediction models may lead to large errors in their forecasts of MCS placement and behavior.

Physical Processes Associated with Heavy Flooding Rainfall in Nashville, Tennessee, and Vicinity during 1–2 May 2010: The Role of an Atmospheric River and Mesoscale Convective Systems

2012 ◽  
Vol 140 (2) ◽  
pp. 358-378 ◽  
Author(s):  
Benjamin J. Moore ◽  
Paul J. Neiman ◽  
F. Martin Ralph ◽  
Faye E. Barthold
Keyword(s):  
Water Vapor ◽  
Heavy Rainfall ◽  
Convective Available Potential Energy ◽  
Mesoscale Convective Systems ◽  
Water Vapor Transport ◽  
Mississippi Valley ◽  
Physical Processes ◽  
Convective Systems ◽  
Atmospheric River ◽  
Mesoscale Convective

A multiscale analysis is conducted in order to examine the physical processes that resulted in prolonged heavy rainfall and devastating flash flooding across western and central Tennessee and Kentucky on 1–2 May 2010, during which Nashville, Tennessee, received 344.7 mm of rainfall and incurred 11 flood-related fatalities. On the synoptic scale, heavy rainfall was supported by a persistent corridor of strong water vapor transport rooted in the tropics that was manifested as an atmospheric river (AR). This AR developed as water vapor was extracted from the eastern tropical Pacific and the Caribbean Sea and transported into the central Mississippi Valley by a strong southerly low-level jet (LLJ) positioned between a stationary lee trough along the eastern Mexico coast and a broad, stationary subtropical ridge positioned over the southeastern United States and the subtropical Atlantic. The AR, associated with substantial water vapor content and moderate convective available potential energy, supported the successive development of two quasi-stationary mesoscale convective systems (MCSs) on 1 and 2 May, respectively. These MCSs were both linearly organized and exhibited back-building and echo-training, processes that afforded the repeated movement of convective cells over the same area of western and central Tennessee and Kentucky, resulting in a narrow band of rainfall totals of 200–400 mm. Mesoscale analyses reveal that the MCSs developed on the warm side of a slow-moving cold front and that the interaction between the southerly LLJ and convectively generated outflow boundaries was fundamental for generating convection.

scholarly journals Spatiotemporal Characteristics and Large-Scale Environments of Mesoscale Convective Systems East of the Rocky Mountains

2019 ◽  
Vol 32 (21) ◽  
pp. 7303-7328 ◽  
Author(s):  
Zhe Feng ◽  
Robert A. Houze ◽  
L. Ruby Leung ◽  
Fengfei Song ◽  
Joseph C. Hardin ◽  
...  
Keyword(s):  
Great Plains ◽  
Rocky Mountains ◽  
Large Scale ◽  
Mesoscale Convective Systems ◽  
Rain Area ◽  
Stratiform Rain ◽  
Convective Systems ◽  
Mesoscale Convective ◽  
The U.S ◽  
Mcs Genesis

ABSTRACT The spatiotemporal variability and three-dimensional structures of mesoscale convective systems (MCSs) east of the U.S. Rocky Mountains and their large-scale environments are characterized across all seasons using 13 years of high-resolution radar and satellite observations. Long-lived and intense MCSs account for over 50% of warm season precipitation in the Great Plains and over 40% of cold season precipitation in the southeast. The Great Plains has the strongest MCS seasonal cycle peaking in May–June, whereas in the U.S. southeast MCSs occur year-round. Distinctly different large-scale environments across the seasons have significant impacts on the structure of MCSs. Spring and fall MCSs commonly initiate under strong baroclinic forcing and favorable thermodynamic environments. MCS genesis frequently occurs in the Great Plains near sunset, although convection is not always surface based. Spring MCSs feature both large and deep convection, with a large stratiform rain area and high volume of rainfall. In contrast, summer MCSs often initiate under weak baroclinic forcing, featuring a high pressure ridge with weak low-level convergence acting on the warm, humid air associated with the low-level jet. MCS genesis concentrates east of the Rocky Mountain Front Range and near the southeast coast in the afternoon. The strongest MCS diurnal cycle amplitude extends from the foothills of the Rocky Mountains to the Great Plains. Summer MCSs have the largest and deepest convective features, the smallest stratiform rain area, and the lowest rainfall volume. Last, winter MCSs are characterized by the strongest baroclinic forcing and the largest MCS precipitation features over the southeast. Implications of the findings for climate modeling are discussed.

Variation of Lightning and Convective Rain Fraction in Mesoscale Convective Systems of the MJO

2015 ◽  
Vol 72 (5) ◽  
pp. 1932-1944 ◽  
Author(s):  
Katrina S. Virts ◽  
Robert A. Houze
Keyword(s):  
Tropical Rainfall Measuring Mission ◽  
Mesoscale Convective Systems ◽  
Weather Forecasts ◽  
Stratiform Rain ◽  
Convective Systems ◽  
Earth Observing System ◽  
Mesoscale Convective ◽  
Moderate Resolution ◽  
The Indian Ocean ◽  
Moderate Resolution Imaging Spectroradiometer

Abstract Characteristics of mesoscale convective systems (MCSs) in regions affected by the Madden–Julian oscillation (MJO) are investigated using a database of MCSs observed by the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Advanced Microwave Scanning Radiometer for Earth Observing System (AMSR-E). Lightning occurrence detected by the World-Wide Lightning Location Network (WWLLN) is composited in a framework centered on the MCSs. During MJO active periods, MCSs are more numerous and larger, as the convective features persist and attain greater horizontal scales. Anomalies of the lifted index, derived from the European Centre for Medium-Range Weather Forecasts (ECMWF) interim reanalysis (ERA-Interim) fields, indicate that MCS environments are more stable during MJO active periods. Over the Indian Ocean, Maritime Continent, and western Pacific, lightning density in an MCS maximizes during the time that the total number of systems begins to increase as the MJO is beginning to be more active, implying both more vigorous convection and less extensive stratiform rain areas at this transitional time of the MJO. The peak in MJO precipitation coincides with peak occurrence of interconnected MCSs with larger stratiform rain fraction, shown by the Tropical Rainfall Measuring Mission satellite, while composites of lightning frequency show that during MJO active periods the zone of lightning is contracted around the centers of MCSs, and flashes are less frequent.

Mesoscale Convective Systems and Critical Clusters

2009 ◽  
Vol 66 (9) ◽  
pp. 2913-2924 ◽  
Author(s):  
Ole Peters ◽  
J. David Neelin ◽  
Stephen W. Nesbitt
Keyword(s):  
Water Vapor ◽  
Critical Region ◽  
Mesoscale Convective Systems ◽  
Quantitative Prediction ◽  
Radius Of Gyration ◽  
Size Distributions ◽  
Onset Of Convection ◽  
Convective Systems ◽  
Radar Images ◽  
Mesoscale Convective

Abstract Size distributions and other geometric properties of mesoscale convective systems (MCSs), identified as clusters of adjacent pixels exceeding a precipitation threshold in satellite radar images, are examined with respect to a recently identified critical range of water vapor. Satellite microwave estimates of column water vapor and precipitation show that the onset of convection and precipitation in the tropics can be described as a phase transition, where the rain rate and likelihood of rainfall suddenly increase as a function of water vapor. This is confirmed in Tropical Rainfall Measuring Mission radar data used here. Percolation theory suggests that cluster properties should be highly sensitive to changes in the density of occupied pixels, which here translates into a rainfall probability, which in turn sensitively depends on the water vapor. To confirm this, clusters are categorized by their prevalent water vapor. As expected, mean cluster size and radius of gyration strongly increase as the critical water vapor is approached from below. In the critical region one finds scale-free size distributions spanning several orders of magnitude. Large clusters are typically from the critical region: at low water vapor most clusters are small, and supercritical water vapor values are too rare to contribute much. The perimeter of the clusters confirms previous observations in satellite, field, and model data of robust nontrivial scaling. The well-known area–perimeter scaling is fully compatible with the quantitative prediction from the plausible null model of gradient percolation, where the accessible hull is a fractal object with dimension 4/3.

scholarly journals Organization and Environmental Properties of Extreme-Rain-Producing Mesoscale Convective Systems

2005 ◽  
Vol 133 (4) ◽  
pp. 961-976 ◽  
Author(s):  
Russ S. Schumacher ◽  
Richard H. Johnson
Keyword(s):  
The United States ◽  
Radar Reflectivity ◽  
Mesoscale Convective Systems ◽  
Surface Boundary ◽  
Stratiform Rain ◽  
Convective Systems ◽  
Precipitation Total ◽  
Mesoscale Convective ◽  
Extreme Rain ◽  
Reflectivity Data

This study examines the radar-indicated structures and other features of extreme rain events in the United States over a 3-yr period. A rainfall event is defined as “extreme” when the 24-h precipitation total at one or more stations surpasses the 50-yr recurrence interval amount for that location. This definition yields 116 such cases from 1999 to 2001 in the area east of the Rocky Mountains, excluding Florida. Two-kilometer national composite radar reflectivity data are then used to examine the structure and evolution of each extreme rain event. Sixty-five percent of the total number of events are associated with mesoscale convective systems (MCSs). While a wide variety of organizational structures (as indicated by radar reflectivity data) are seen among the MCS cases, two patterns of organization are observed most frequently. The first type has a line, often oriented east–west, with “training” convective elements. It also has a region of adjoining stratiform rain that is displaced to the north of the line. The second type has a back-building or quasi-stationary area of convection that produces a region of stratiform rain downstream. Surface observations and composite analysis of Rapid Update Cycle Version 2 (RUC-2) model data reveal that training line/adjoining stratiform (TL/AS) systems typically form in a very moist, unstable environment on the cool side of a preexisting slow-moving surface boundary. On the other hand, back-building/quasi-stationary (BB) MCSs are more dependent on mesoscale and storm-scale processes, particularly lifting provided by storm-generated cold pools, than on preexisting synoptic boundaries.

scholarly journals Microphysical and Thermodynamic Structure and Evolution of the Trailing Stratiform Regions of Mesoscale Convective Systems during BAMEX. Part I: Observations

2009 ◽  
Vol 137 (4) ◽  
pp. 1165-1185 ◽  
Author(s):  
Andrea M. Smith ◽  
Greg M. McFarquhar ◽  
Robert M. Rauber ◽  
Joseph A. Grim ◽  
Michael S. Timlin ◽  
...  
Keyword(s):  
Life Cycle ◽  
Mesoscale Convective Systems ◽  
Melting Layer ◽  
Thermodynamic Structure ◽  
Stratiform Rain ◽  
Convective Systems ◽  
Horizontal Flight ◽  
Bow Echo ◽  
Mesoscale Convective ◽  
Mesoscale Convective Vortex

Abstract This study used airborne and ground-based radar and optical array probe data from the spiral descent flight patterns and horizontal flight legs of the NOAA P-3 aircraft in the trailing stratiform regions (TSRs) of mesoscale convective systems (MCSs) observed during the Bow Echo and Mesoscale Convective Vortex Experiment (BAMEX) to characterize microphysical and thermodynamic variations within the TSRs in the context of the following features: the transition zone, the notch region, the enhanced stratiform rain region, the rear anvil region, the front-to-rear flow, the rear-to-front flow, and the rear inflow jet axis. One spiral from the notch region, nine from the enhanced stratiform rain region, and two from the rear anvil region were analyzed along with numerous horizontal flight legs that traversed these zones. The spiral performed in the notch region on 29 June occurred early in the MCS life cycle and exhibited subsaturated conditions throughout its depth. The nine spirals performed within the enhanced stratiform rain region exhibited saturated conditions with respect to ice above and within the melting layer and subsaturated conditions below the melting layer. Spirals performed in the rear anvil region showed saturation until the base of the anvil, near −1°C, and subsaturation below. These data, together with analyses of total number concentration and the slope to gamma fits to size distributions, revealed that sublimation above the melting layer occurs early in the MCS life cycle but then reduces in importance as the environment behind the convective line is moistened from the top down. Evaporation below the melting layer was insufficient to attain saturation below the melting layer at any time or location within the MCS TSRs. Relative humidity was found to have a strong correlation to the component of wind parallel to the storm motion, especially within air flowing from front to rear.

Clouds and Water Vapor in the Tropical Tropopause Transition Layer over Mesoscale Convective Systems

2015 ◽  
Vol 72 (12) ◽  
pp. 4739-4753 ◽  
Author(s):  
Katrina S. Virts ◽  
Robert A. Houze
Keyword(s):  
Water Vapor ◽  
Transition Layer ◽  
Mesoscale Convective Systems ◽  
Convective Systems ◽  
Tropical Tropopause ◽  
Mesoscale Convective ◽  
Ice Content ◽  
Radial Outflow ◽  
Cold Point ◽  
Ice Water

Abstract Observations from A-Train satellites and other datasets show that mesoscale convective systems (MCSs) affect the water vapor and ice content of the tropical tropopause transition layer (TTL). The largest MCSs with radar reflectivity characteristics consistent with the presence of large stratiform and anvil regions have the greatest impact. Most MCSs are associated with clouds in the TTL. Composites in MCS-relative coordinates indicate enhanced cloudiness and ice water content (IWC) extending toward the cold-point tropopause (CPT), particularly in large and connected MCSs. Widespread anvils in the lower TTL are evident in the peak cloudiness diverging outward at those levels. Upper-tropospheric water vapor concentrations are enhanced near MCSs. Close to the centers of MCSs, water vapor is suppressed at TTL base, likely because of the combined effects of reduced moistening or dehydration at the higher TTL relative humidities and subsidence above cloud top. Weak moistening is observed near the CPT, consistent with sublimation of ice crystals at the tops of the deepest MCSs. In the outflow region, moistening is observed in the lower TTL near the largest MCSs. Enhanced water vapor in the upper troposphere and lower TTL extends beyond the area of substantially enhanced cloudiness and IWC, in agreement with the observed radial outflow, indicating that MCSs are injecting water vapor into the environment and consistent with the possibility that MCS development may be favored by a premoistened environment.

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