A preliminary experiment on the simulation A preliminary experiment on the simulation of thunderstorm electrification through GRof thunderstorm electrification through GRAPES APES

Yijun Zhang

Chinese Academy of Meteorological Sciences, Beijing, China

The Lightning discharges occurs in thunderstorm

The characteristic of lightning is important to understand the occurrence of severe storm

Lightning data is a good information for nowcasting of severe storm

Introduction

The cloud electrification and discharge process has been paid long lasting attention. The non-inductive and inductive charging are the dominant mechanisms by which charge centers are formed. The mechanisms involves rebounding collisions between graupel and ice crystals. For non-inductive charging, Laboratory experiments indicated the charge transfer per collision depend on size of the ice crystals and the fall-speed of the graupel, while the charge sign depends on temperature and the liquid water content. The results of different experiments are conflicting in the details. To compare and evaluate charge separation parameterizations, an numerical simulation study was conducted .

Introduction

Method

A 3-dimensional thunderstorm electrification and lightning model (TELM) was developed.

The model included cloud dynamics, microphysics and electrical processes.

Eight microphysical processes are condensation, deposition, evaporation, autoconversion of cloud-rain, collection, freezing, melting, nucleation and multiplication of ice crystals.

The electrification scheme with both non-inductive and inductive charging mechanisms are considered.

The bi-directional lightning parameterization scheme is used.

1) Thundercloud Model

GRAPES (short form Global/Regional Assimilation and Prediction System) is the new generation of numerical forecast model developed by China Meteorological Administration (CMA). It is the multi-scale and universal numerical model which also can realize the variational data assimilation.

Using GRAPES to provide the TELM with ambient field to substitute for the initial field obtained from sounding data and warm bubble with randomized thermal perturbations.

2) Initial Field

Results

GRAPES was first run 6-8 hours to obtain prognostic field which was regarded as the initial field to run the TELM by starting the convection. The results indicated that the convection core and high density region of graupel and ice crystals were in agreement with strong charge density core. And at the same time, the charge structure was valid, too.

Cloud with tripole charge structure, where white solid line is for graupel and ice crystals, dashed line for ice crystals , black line for wind field.

NCG(a) and PCG(b), where blue line is for negative leader, red line for positive leader, dashed line for cloud confines, solid for positive charge, and dotted for negative charge.

It is indicated that NCG is related to the positive charge region in the lower part of cloud, while PCG often occurs in the negative charge region of the lower part of cloud.

Comparison of different parameterizations

Different parameterizations of non-inductive and inductive charging are compared.

Three inductive charging strengths are used here: non (no inductive charging), moderate (mod) and strong (str).

Three non-inductive charging parameterizations

Three non-inductive charging parameterizations (graupel-crystal).

Takahashi scheme

Saunders scheme

Gardiner scheme

Gardiner scheme

Dipolar charge structure

Takahashi scheme

Dipolar charge structurechange to inverted dipolar charge structure

Saunders scheme

Dipolar charge structure

Gard/non charge concentrati

on

Gard/str charge concentrati

on

Taka/noncharge

concentration

Taka/str charge concentrati

on

Table.1. Summary of total lightning for each simulation.

There were no CG flashes when inductive charging was turned off.

Significant numbers of CG flashes were produced only with the stronger inductive charging parameters.

Through the combination of TELM and GRAPES, the lightning activity of thunderstorm can be simulated.

Non-inductive charging parameterizations constitute important factors in affecting the electrification of thunderstorm.

Inductive charging parameterizations also play a certain role in the lightning activity of thunderstorm.

Conclusion

This paper presented preliminary results, the further study need that results of numerical simulation compared to the results of field observations.

Thank you