Studies on Lower Atmospheric Processes over South India using Numerical Atmospheric Models and Experiments

Contents

1. Introduction

1.1 General Introduction

1.2 Criticalities involved in the various Atmospheric Events

1.2.1 Scales of Atmospheric Motion

1.2.2 Rapid changes in Atmospheric Parameterization

1.2.3 Computing Requirements

1.2.4 Dissemination of Forecast Product to the User’s Community

1.3 Examples of some Mesoscale Atmospheric Processes

1.3.1 Density or Gravity Current

1.3.2 Tropical Cyclones

1.3.3 Thunderstorms

1.3.4 Squall Lines

1.3.5 Tornadoes

1.3.6 Sea/Land Breezes

1.3.7 Gravity or Buoyancy Waves

1.3.8 Mountain/Lee Waves

1.3.9 Slope and Valley Winds

1.4 History of Numerical Weather Prediction (NWP)

1.5 Potentials of Atmospheric Model

1.6 Objective of the Thesis

1.7 Organization of the Thesis

2. Numerical Atmospheric Models used in the Study

2.1 General Introduction

2.1.1 What is an ‘Atmospheric Model’?

2.1.2 Limitations of NWP Models

2.2 Basic Classification of Atmospheric Models

2.2.1 Hydrostatic Approximation

2.2.2 Atmospheric Model classification

2.3 High-resolution Regional Model (HRM)

2.3.1 Differential form of the Model Equations

2.3.2 Physical Parameterization

2.3.2.1 Radiation and Clouds

2.3.2.2 Grid Scale Precipitation

2.3.2.3 Convection

2.3.2.4 Turbulent Fluxes in ABL and Free Atmosphere

2.3.2.5 Soil Model

2.3.3 Operational Use of HRM based on GME Data

2.4 Advanced Regional Prediction System (ARPS)

2.4.1 Dynamic Equations and Numerical Formulation

2.4.1.1 The Coordinate System

2.4.1.2 Governing Equations

2.4.2 Parameterization

2.4.2.1 Sub-grid Scale Turbulence

2.4.2.2 Microphysics

2.4.2.3 Planetary Boundary Layer Depth

2.4.2.4 Surface Flux

2.4.2.5 Land Surface Energy and Soil Vegetation

2.4.2.6 Cumulus Parameterization

2.4.3 Boundary Conditions

2.4.3.1 Lateral Boundary Conditions

2.4.3.2 Top and Bottom Boundary Conditions

2.5 Comparison between HRM and ARPS

2.6 Limitations of HRM and ARPS

2.7 Rationale Behind the Choice of the Models

2.8 Discussion

3. Statistical Assessment of Atmospheric Models used in the Study

3.1 General Introduction

3.2 Methodology of Evaluation of Statistical Bias and its Significance

3.2.1 Model Bias and Simulation Errors: General Introduction

3.2.2 Statistical Significance of the Model Bias

3.2.3 Normalization of Model Bias

3.2.4 Incorporation of Model Bias in Near Real Time Simulations

3.2.5 Statistical Skill Parameters: Correlation Coefficient and Root Mean Square Error (RMSE)

3.3 Statistical Evaluation of HRM forecast fields

3.3.1 Error Analysis for the Entire Domain

3.3.2 Methodology

3.3.3 Model Performance for +24 hours and +48 hours simulations

3.3.4 Monthly Mean Normalized Bias in different Seasons

3.3.5 Evaluation of the Performance of the Model in the Entire Domain during different seasons

3.3.6 Model Bias over SHAR and Trivandrum

3.4 Sensitivity of ARPS to the Initial Conditions and its Impact on the forecast fields

3.5 Discussion

4. Characterization of Sea/Land Breeze Circulation Along the West Coast of Indian Sub-continent

4.1 General Introduction

4.2 Sea/Land Breeze Circulation

4.3 SLBC over the West Coast of Indian Sub-continent: A Review

4.4 Domain of Study and Definition of Sea Breeze Component

4.5 Data

4.5.1 Model Data

4.5.2 Ship Data

4.5.3 IMD Data

4.6 Results

4.6.1 Thermal and wind structure of SLBC over Ocean and Land

4.6.2 Numerical Simulation of SLBC characteristics during pre-monsoon and winter

4.6.2.1 Diurnal Variation of Sea/Land Breeze Component

4.6.2.2 Spatial Variation of Sea Breeze component

4.6.2.3 Spatial variation of Boundary Layer Height within the SLBC

4.7 Discussion

5. Mountain Wave Activity Over the Western Ghats of Indian Sub-continent

5.1 General Introduction

5.2 Mountain Wave Projects

5.3 Mountain Waves and their Significance

5.4 Domain of Study and Database

5.5 Theory

5.5.1 Mountain Waves

5.5.2 Orographic Lifting

5.6 Results

5.6.1 Froude Number

5.6.2 Scorer Parameter

5.6.3 Vertical Propagation and Wave Breaking Characteristics from the Model Simulations

5.6.4 Vertical Momentum Flux

5.7 Discussion

6. Thunderstorm Over the East and West Coast of Indian Sub-continent: A Case Study

6.1 General Introduction

6.2 Thunderstorm: Some Meteorological Aspects

6.2.1 What is a Thunderstorm?

6.2.2 Related Natural Hazards and Meteorological Importance

6.2.3 Precursors to Thunderstorm Occurrence

6.2.3.1 Triggering Mechanism

6.2.3.2 Conditional Instability

6.2.3.3 High Dew-point Temperature

6.2.3.4 Low-level Wind Shear

6.2.4 Life Cycle of Thunderstorm

6.3 A Review of thunderstorm Studies

6.4 Thunderstorm Events over SHAR and Trivandrum: Typical case Study

6.5 Model Configuration

6.6 Results

6.6.1 Prediction of Thunderstorm over SHAR: A Case Study

6.6.1.1 Prevailing Conditions

6.6.1.2 Model Simulations

6.6.1.2.1 Surface Level Horizontal Divergence

6.6.1.2.2 Pressure Perturbation

6.6.1.2.3 Vertical Velocity

6.6.1.3 Discussion: Prediction of Thunderstorm

6.6.2 Post Analysis of Thunderstorm event over Trivandrum

6.6.2.1 Meteorological Conditions Prevailing over the Location

6.6.2.2 Elevated Convection

6.6.2.3 Advection of Storms

6.6.2.4 Merger Process

6.6.2.5 Three Numerical Simulation Experiments over Trivandrum

6.6.2.5.1 Experiment 1

6.6.2.5.2 Experiment 2

6.6.2.5.3 Experiment 3

6.6.2.6 Discussion: Post Analysis of Thunderstorm over Trivandrum

6.7 Conclusions

7. Summary and Conclusions

Scope for Future Work

References

Research Objectives and Focus Areas

The primary objective of this thesis is to characterize various lower atmospheric processes—specifically Sea/Land Breeze Circulation (SLBC), Mountain Waves, and Thunderstorms—over the southern part of the Indian Sub-continent using numerical atmospheric models and observational data to bridge gaps in current understanding.

• Numerical modeling of lower atmospheric processes (HRM and ARPS models).
• Statistical assessment and bias evaluation of numerical model forecast fields.
• Characterization of Sea/Land Breeze Circulation (SLBC) along the Indian west coast.
• Study of Mountain Wave dynamics and activity over the Western Ghats.
• Analysis and prediction of Thunderstorm events over the east (SHAR) and west (Trivandrum) coasts of India.

Excerpt from the Book

Summary of Chapters

1. Introduction: Provides a comprehensive background on numerical atmospheric modeling, defining atmospheric scales, processes, and the historical evolution of numerical weather prediction.

2. Numerical Atmospheric Models used in the Study: Introduces the High-resolution Regional Model (HRM) and the Advanced Regional Prediction System (ARPS), detailing their governing equations, parameterizations, and configuration.

3. Statistical Assessment of Atmospheric Models used in the Study: Evaluates the performance of numerical models by analyzing statistical bias and simulation errors, demonstrating how incorporation of monthly mean bias improves model accuracy.

4. Characterization of Sea/Land Breeze Circulation along the West Coast of Indian Sub-continent: Investigates the thermal and wind structure of the Sea/Land Breeze Circulation (SLBC) using HRM simulations and observational data.

5. Mountain Wave Activity Over the Western Ghats of Indian Sub-continent: Examines the genesis and characteristics of mountain waves over the Western Ghats, utilizing Froude Number and Scorer Parameter metrics.

6. Thunderstorm Over the East and West Coast of Indian Sub-continent: A Case Study: Presents case studies of thunderstorm events over SHAR and Trivandrum using ARPS simulations to understand the evolution, propagation, and dissipation of convective systems.

7. Summary and Conclusions: Synthesizes the primary findings of the research and identifies avenues for future scientific work in numerical weather modeling.

Keywords

Numerical Weather Prediction, Mesoscale Models, HRM, ARPS, Atmospheric Boundary Layer, Sea/Land Breeze Circulation, Mountain Waves, Thunderstorms, Statistical Bias Analysis, Orographic Lifting, Convective Instability, Meteorology, India, Western Ghats, Data Assimilation

Frequently Asked Questions

What is the primary focus of this research?

The work focuses on understanding lower atmospheric processes—specifically sea/land breeze, mountain waves, and thunderstorms—over India using numerical atmospheric models.

Which models are utilized in this study?

The study employs the High-resolution Regional Model (HRM) and the Advanced Regional Prediction System (ARPS).

What is the ultimate goal of the thesis?

The goal is to improve the understanding of regional atmospheric phenomena and evaluate the credibility of model-simulated forecast fields.

How is the accuracy of the models assessed?

The study uses systematic statistical bias and error analysis, comparing model outputs against reanalysis fields to quantify and mitigate model errors.

What is the significance of the "Monthly Mean Bias" approach?

Incorporating monthly mean bias estimates into near-real-time simulations helps refine the model outputs, leading to more accurate predictions of temperature and humidity.

How do the researchers study thunderstorms?

They utilize the ARPS model to perform case studies on specific thunderstorm events observed at SHAR and Trivandrum, analyzing thermodynamic parameters like CAPE and CINE.

What role does the Froude Number play in mountain wave analysis?

The Froude Number is used to characterize wind flow over topography, helping to identify conditions that favor mountain wave genesis or wave blocking.

Why are SHAR and Trivandrum selected as study locations?

These locations represent different coastal environments (east vs. west coast) and are critical sites where accurate weather prediction is vital for launch operations and disaster management.

What is the importance of the Scorer Parameter?

The Scorer Parameter serves as an indicator of vertical wave propagation, identifying atmospheric layers where mountain waves can easily propagate versus layers where they are trapped or dissipated.

How does this study contribute to aviation safety?

By identifying and modeling mountain waves and thunderstorm characteristics, the research provides insights that help mitigate hazards like clear-air turbulence and severe down-slope winds.