scholarly journals Relative role of individual variables on a revised Convective System Genesis Parameter over north Indian Ocean with respect to distinct background state

2016 ◽  
Author(s):  
K. G. Sumesh ◽  
S. Abhilash ◽  
M. R. Ramesh Kumar
Keyword(s):  
Indian Ocean ◽  
Large Scale ◽  
Tropical Storms ◽  
Convective System ◽  
Relative Role ◽  
Tropical Ocean ◽  
Low Level ◽  
Individual Variables ◽  
Background State

Abstract. Abstract. Tropical storms are intense low pressure systems that form over warm tropical ocean basins. Depending upon the intensity, they are classified as depressions, cyclones and severe cyclones. Northern Indian Ocean (NIO) is highly prone to intense tropical storms and roughly 5–7 tropical storms are forming over this basin every year. Various Cyclogenesis indices are used to forecast these tropical storms over various basins including NIO. In this aspect we propose a revised Convective System Genesis Parameter (CSGP) to identify regions favourable for storm genesis. The revised CSGP is constructed by using different combinations and thresholds of five variables namely, the Low Level Relative Vorticity, the Low Level Convergence, the Shear co-efficient, the Convective Instability parameter and the Humidity parameter. The relative role of each individual variable on CSGP is analysed separately for different categories of the storms over both Arabian sea and Bay of Bengal. The composite structure of the CSGP for different categories of the storms is further evaluated separately for distinct large scale background state. The results show that the revised CSGP is capable of distinguishing different categories of the storms. The CSGP exhibits large variability during distinct large scale background state. It is also found that the individual variables contribute in a different way during monsoon and non-monsoon seasons. The revised CSGP can be used to forecast all categories of convective systems such as depressions, cyclones and severe cyclones over NIO during the monsoon as well as non-monsoon seasons.

The Role of Equatorial Rossby Waves in Tropical Cyclogenesis. Part I: Idealized Numerical Simulations in an Initially Quiescent Background Environment

2010 ◽  
Vol 138 (4) ◽  
pp. 1368-1382 ◽  
Author(s):  
Jeffrey S. Gall ◽  
William M. Frank ◽  
Matthew C. Wheeler
Keyword(s):  
Tropical Cyclone ◽  
Large Scale ◽  
Phase Speed ◽  
Tropical Cyclogenesis ◽  
Initial Amplitude ◽  
Low Level ◽  
Wave Simulation ◽  
Horizontal Momentum ◽  
Good Agreement

Abstract This two-part series of papers examines the role of equatorial Rossby (ER) waves in tropical cyclone (TC) genesis. To do this, a unique initialization procedure is utilized to insert n = 1 ER waves into a numerical model that is able to faithfully produce TCs. In this first paper, experiments are carried out under the idealized condition of an initially quiescent background environment. Experiments are performed with varying initial wave amplitudes and with and without diabatic effects. This is done to both investigate how the properties of the simulated ER waves compare to the properties of observed ER waves and explore the role of the initial perturbation strength of the ER wave on genesis. In the dry, frictionless ER wave simulation the phase speed is slightly slower than the phase speed predicted from linear theory. Large-scale ascent develops in the region of low-level poleward flow, which is in good agreement with the theoretical structure of an n = 1 ER wave. The structures and phase speeds of the simulated full-physics ER waves are in good agreement with recent observational studies of ER waves that utilize wavenumber–frequency filtering techniques. Convection occurs primarily in the eastern half of the cyclonic gyre, as do the most favorable conditions for TC genesis. This region features sufficient midlevel moisture, anomalously strong low-level cyclonic vorticity, enhanced convection, and minimal vertical shear. Tropical cyclogenesis occurs only in the largest initial-amplitude ER wave simulation. The formation of the initial tropical disturbance that ultimately develops into a tropical cyclone is shown to be sensitive to the nonlinear horizontal momentum advection terms. When the largest initial-amplitude simulation is rerun with the nonlinear horizontal momentum advection terms turned off, tropical cyclogenesis does not occur, but the convectively coupled ER wave retains the properties of the ER wave observed in the smaller initial-amplitude simulations. It is shown that this isolated wave-only genesis process only occurs for strong ER waves in which the nonlinear advection is large. Part II will look at the more realistic case of ER wave–related genesis in which a sufficiently intense ER wave interacts with favorable large-scale flow features.

scholarly journals More on the Scale Dependence of the Predictability of Precipitation Patterns: Extension to the 2009–13 CAPS Spring Experiment Ensemble Forecasts

2017 ◽  
Vol 145 (9) ◽  
pp. 3625-3646 ◽  
Author(s):  
Madalina Surcel ◽  
Isztar Zawadzki ◽  
M. K. Yau ◽  
Ming Xue ◽  
Fanyou Kong
Keyword(s):  
Large Scale ◽  
Forecast Error ◽  
Quasi Equilibrium ◽  
Relative Role ◽  
Ensemble Forecasts ◽  
Adjustment Time ◽  
Convective Adjustment ◽  
Microphysical Parameterization ◽  
Microphysical Parameterization Scheme

This paper analyzes the scale and case dependence of the predictability of precipitation in the Storm-Scale Ensemble Forecast (SSEF) system run by the Center for Analysis and Prediction of Storms (CAPS) during the NOAA Hazardous Weather Testbed Spring Experiments of 2008–13. The effect of different types of ensemble perturbation methodologies is quantified as a function of spatial scale. It is found that uncertainties in the large-scale initial and boundary conditions and in the model microphysical parameterization scheme can result in the loss of predictability at scales smaller than 200 km after 24 h. Also, these uncertainties account for most of the forecast error. Other types of ensemble perturbation methodologies were not found to be as important for the quantitative precipitation forecasts (QPFs). The case dependences of predictability and of the sensitivity to the ensemble perturbation methodology were also analyzed. Events were characterized in terms of the extent of the precipitation coverage and of the convective-adjustment time scale [Formula: see text], an indicator of whether convection is in equilibrium with the large-scale forcing. It was found that events characterized by widespread precipitation and small [Formula: see text] values (representative of quasi-equilibrium convection) were usually more predictable than nonequilibrium cases. No significant statistical relationship was found between the relative role of different perturbation methodologies and precipitation coverage or [Formula: see text].

scholarly journals Relative role of El Niño and IOD forcing on the southern tropical Indian Ocean Rossby waves

2014 ◽  
Vol 119 (8) ◽  
pp. 5105-5122 ◽  
Author(s):  
Soumi Chakravorty ◽  
C. Gnanaseelan ◽  
J. S. Chowdary ◽  
Jing-Jia Luo
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
Rossby Waves ◽  
El Nino ◽  
Tropical Indian Ocean ◽  
Relative Role

Quantification of the relative role of land-surface processes and large-scale forcing in dynamic downscaling over the Tibetan Plateau

2016 ◽  
Vol 48 (5-6) ◽  
pp. 1705-1721 ◽  
Author(s):  
Yanhong Gao ◽  
Linhong Xiao ◽  
Deliang Chen ◽  
Fei Chen ◽  
Jianwei Xu ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Land Surface ◽  
Large Scale ◽  
Surface Processes ◽  
The Tibetan Plateau ◽  
Relative Role ◽  
Dynamic Downscaling ◽  
Land Surface Processes

scholarly journals Kinematic and Precipitation Characteristics of Convective Systems Observed by Airborne Doppler Radar during the Life Cycle of a Madden–Julian Oscillation in the Indian Ocean

2014 ◽  
Vol 142 (4) ◽  
pp. 1385-1402 ◽  
Author(s):  
Nick Guy ◽  
David P. Jorgensen
Keyword(s):  
Indian Ocean ◽  
Doppler Radar ◽  
Convective System ◽  
Dynamical Structure ◽  
Madden Julian Oscillation ◽  
Tropical Ocean ◽  
Convective Systems ◽  
Toga Coare ◽  
Stratiform Precipitation ◽  
The Indian Ocean

Abstract This study presents characteristics of convective systems observed during the Dynamics of the Madden–Julian oscillation (DYNAMO) experiment by the instrumented NOAA WP-3D aircraft. Nine separate missions, with a focus on observing mesoscale convective systems (MCSs), were executed to obtain data in the active and inactive phase of a Madden–Julian oscillation (MJO) in the Indian Ocean. Doppler radar and in situ thermodynamic data are used to contrast the convective system characteristics during the evolution of the MJO. Isolated convection was prominent during the inactive phases of the MJO, with deepening convection during the onset of the MJO. During the MJO peak, convection and stratiform precipitation became more widespread. A larger population of deep convective elements led to a larger area of stratiform precipitation. As the MJO decayed, convective system top heights increased, though the number of convective systems decreased, eventually transitioning back to isolated convection. A distinct shift of echo top heights and contoured frequency-by-altitude diagram distributions of radar reflectivity and vertical wind speed indicated that some mesoscale characteristics were coupled to the MJO phase. Convective characteristics in the climatological initiation region (Indian Ocean) were also apparent. Comparison to results from the Tropical Ocean and Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE) in the western Pacific indicated that DYNAMO MCSs were linearly organized more parallel to the low-level shear and without strong cold pools than in TOGA COARE. Three-dimensional MCS airflow also showed a different dynamical structure, with a lack of the descending rear inflow present in shear perpendicularly organized TOGA COARE MCSs. Weaker, but deeper updrafts were observed in DYNAMO.

Remote influences on the Indian monsoon Low-Level Jet intraseasonal variations

2020 ◽  
Author(s):  
Takeshi Izumo ◽  
Maratt Satheesan Swathi ◽  
Matthieu Lengaigne ◽  
Jérôme Vialard ◽  
Dr Ramesh Kumar
Keyword(s):  
Indian Ocean ◽  
Indian Summer Monsoon ◽  
Arabian Sea ◽  
Large Scale ◽  
Indian Monsoon ◽  
Westerly Wind ◽  
Low Level ◽  
Intraseasonal Variations ◽  
The Indian Ocean ◽  
Low Level Jet

<p>A strong Low-Level Jet (LLJ), also known as the Findlater jet, develops over the Arabian Sea during the Indian summer monsoon. This jet is an essential source of moisture for monsoonal rainfall over the densely-populated Indian subcontinent and is a key contributor to the Indian Ocean oceanic productivity by sustaining the western Arabian Sea upwelling systems. The LLJ intensity fluctuates intraseasonally within the ~20- to 90-day band, in relation with the northward-propagating active and break phases of the Indian summer monsoon. Our observational analyses reveal that these large-scale regional convective perturbations  only explain about half of the intraseasonal LLJ variance, the other half being unrelated to large-scale convective perturbations over the Indian Ocean. We show that convective fluctuations in two regions outside the Indian Ocean can remotely force a LLJ intensification, four days later. Enhanced atmosphericdeep convection over the northwestern tropical Pacific yields westerly wind anomalies that propagate westward to the Arabian Sea as baroclinic atmospheric Rossby Waves. Suppressed convection over the eastern Pacific / North American monsoon region yields westerly wind anomalies that propagate eastward to the Indian Ocean as dry baroclinic equatorial Kelvin waves. Those largely independent remote influences jointly explain ~40% of the intraseasonal LLJ variance that is not related to convective perturbations over the Indian Ocean (i.e. ~20% of the total), with the northwestern Pacific contributing twice as much as the eastern Pacific. Taking into account these two remote influences should thus enhance the ability to predict the LLJ.</p><p> </p><p>Related reference: Swathi M.S, Takeshi Izumo, Matthieu Lengaigne, Jérôme Vialard and M.R. Ramesh Kumar:Remote influences on the Indian monsoon Low-Level Jet intraseasonal variations, accepted in Climate Dynamics.</p>

Weathering the Soviet Countryside: The Impact of Climate and Agricultural Policies on Russian Grain Yields, 1958–2010

2013 ◽  
Vol 40 (1) ◽  
pp. 115-143 ◽  
Author(s):  
Nikolai M. Dronin ◽  
Andrei P. Kirilenko
Keyword(s):  
Large Scale ◽  
State Level ◽  
Relative Role ◽  
Agricultural Policies ◽  
Production Potential ◽  
Russian Agriculture ◽  
Land Privatization ◽  
History Of ◽  
The Impact

Agriculture in Russia has always had to contend with unfavorable climate. At the same time, large-scale socio-economic experiments have also strained the country’s food production potential throughout the 20th century. The relative role of climate and state agricultural policies in affecting production of cereals was studied for the period of 1958–2010. The study used statistical yield modeling to explain the variations in observed yields with slowly changing progress in technology and management and weather variability. The correlation between the actual and weather-explained yields is moderate to high: measured at the level of the entire country, Pearson’s r is 0.74 and Spearman’s rho is 0.68. Further, we suggest that the residual yield variability can be explained partially with the influence of large-scale changes in agricultural policies at the state level. Between these policies, we consider the following key periods in the history of Russian agriculture: “Virgin Lands” campaign (end of 1950s), Kosygin-Liberman initiatives (late 1960s), Brezhnev’s investment programmes in response of stagnation of agriculture (late 1970s – early 1980s), Gorbachev’s “Perestrojka” (1985–1991), and land privatization and price liberalization (1990s).

scholarly journals Potential Large-Scale Forcing Mechanisms Driving Enhanced North Atlantic Tropical Cyclone Activity since the Mid-1990s

2018 ◽  
Vol 31 (4) ◽  
pp. 1377-1397 ◽  
Author(s):  
Haikun Zhao ◽  
Xingyi Duan ◽  
G. B. Raga ◽  
Fengpeng Sun
Keyword(s):  
Tropical Cyclone ◽  
North Atlantic ◽  
Large Scale ◽  
Vertical Wind Shear ◽  
Low Level ◽  
The North ◽  
Recent Increase ◽  
Forcing Mechanisms ◽  
Interdecadal Changes

A significant increase of tropical cyclone (TC) frequency is observed over the North Atlantic (NATL) basin during the recent decades (1995–2014). In this study, the changes in large-scale controls of the NATL TC activity are compared between two periods, one before and one since 1995, when a regime change is observed. The results herein suggest that the significantly enhanced NATL TC frequency is related mainly to the combined effect of changes in the magnitudes of large-scale atmospheric and oceanic factors and their association with TC frequency. Interdecadal changes in the role of vertical wind shear and local sea surface temperatures (SSTs) over the NATL appear to be two important contributors to the recent increase of NATL TC frequency. Low-level vorticity plays a relatively weak role in the recent increase of TC frequency. These changes in the role of large-scale factors largely depend on interdecadal changes of tropical SST anomalies (SSTAs). Enhanced low-level westerlies to the east of the positive SSTAs have been observed over the tropical Atlantic since 1995, with a pattern nearly opposite to that seen before 1995. Moreover, the large-scale contributors to the NATL TC frequency increase since 1995 are likely related to both local and remote SSTAs. Quantification of the impacts of local and remote SSTAs on the increase of TC frequency over the NATL basin and the physical mechanisms require numerical simulations and further observational analyses.

Cyclogenesis Simulation of Typhoon Prapiroon (2000) Associated with Rossby Wave Energy Dispersion*

2010 ◽  
Vol 138 (1) ◽  
pp. 42-54 ◽  
Author(s):  
Xuyang Ge ◽  
Tim Li ◽  
Melinda S. Peng
Keyword(s):  
Rossby Wave ◽  
Wave Energy ◽  
Large Scale ◽  
Wave Train ◽  
Energy Dispersion ◽  
Sensitivity Experiment ◽  
Low Level ◽  
Filtering Technique ◽  
Upper Level

Abstract The genesis of Typhoon Prapiroon (2000), in the western North Pacific, is simulated to understand the role of Rossby wave energy dispersion of a preexisting tropical cyclone (TC) in the subsequent genesis event. Two experiments are conducted. In the control experiment (CTL), the authors retain both the previous typhoon, Typhoon Bilis, and its wave train in the initial condition. In the sensitivity experiment (EXP), the circulation of Typhoon Bilis was removed based on a spatial filtering technique of Kurihara et al., while the wave train in the wake is kept. The comparison between these two numerical simulations demonstrates that the preexisting TC impacts the subsequent TC genesis through both a direct and an indirect process. The direct process is through the conventional barotropic Rossby wave energy dispersion, which enhances the low-level wave train, the boundary layer convergence, and the convection–circulation feedback. The indirect process is through the upper-level outflow jet. The asymmetric outflow jet induces a secondary circulation with a strong divergence tendency to the left-exit side of the outflow jet. The upper-level divergence boosts large-scale ascending motion and promotes favorable environmental conditions for a TC-scale vortex development. In addition, the outflow jet induces a well-organized cyclonic eddy angular momentum flux, which acts as a momentum forcing that enhances the upper-level outflow and low-level inflow and favors the growth of the new TC.

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