Hurricane Electrification Experiment

This document is divided into 3 sections:

Program Significance

Cloud electrification has been a topic of great scientific interest for many years, but the lack of suitable instruments for measuring electric fields and particle charges in clouds has hindered research. From anecdotal evidence, meteorologists have cons idered that hurricanes usually have little electrical activity. However, the introduction of lightning detection systems along the U. S. coast has resulted in several case studies of cloud-to-ground (CG) lightning from tropical storms and hurricanes. Th ese data show that a larger proportion of tropical cyclones produce lightning than was previously known. Intensifying tropical cyclones tend to be particularly electrically active. For example, the lightning detection network at Kennedy Space Center, Flo rida, detected a dramatic increase in the CG lightning rate in Hurricane Diana (1984) when the storm intensified from tropical storm to hurricane strength. However, many hurricanes exhibit little or no electrical activity.

The charge separation mechanisms that results in the electrical activity in hurricanes are poorly understood. Electrification studies will be aided by the recent additions of four rotating vane field mills and an induction ring on the WP-3D. The field mi lls measure the vector electric field and the induction ring measures the charge on individual particles. The Doppler radar on the aircraft provides three-dimensional wind fields. Also, the National Lightning Detection Network (NLDN) can provide locations of CG lightning in tropical cyclones near the U. S. coast. With the new instrumentation and Doppler radar data, this experiment will increase understanding of electrical processes in tropical cyclones and provide insights into the relationships between v ertical motions, cloud microphysics, lightning, and storm intensity.

Objectives

The objectives of this experiment are to study the temporal evolution of the electric field and microphysical and kinematic properties in tropical cyclones. The specific goals are:
  1. Measure the sign and magnitude of the vector electric field near the eyewall and in an outer convective rainband.
  2. Document the three-dimensional wind field in electrified clouds, including the vertical winds estimated from the Doppler radar.
  3. Determine the polarity and magnitude of the charge on ice precipitation at several temperature levels above the melting level.
  4. Estimate the transport of electrical charge in the storm.
  5. Record the types and concentrations of all particle types observed in the electrically active portions of the storm.

Mission Description

This experiment documents the microphysical characteristics of electrically active convection using a single aircraft. The new Particle Measuring System (PMS) 2-D greyscale probes, the new PMS FSSP-100, and the DRI field mills are essential. The DRI induc tion ring, the tail Doppler radar, and the cloud liquid water probes [JW (Johnson-Williams) and King] are highly desirable. Horizontal and vertical wind field measurements will be obtained from the Doppler radar. The aircraft should execute a standard TAS calibration (Fig. C-l ) in clear air prior to entering the storm if conditions permit.

This study requires that one aircraft be equipped with the DRI electric field instruments in addition to the standard instrumentation. The PMS probes must be the best available, and the radars must be fully operational. The experiment is composed of three options. In all options, it is desirable to have 4 to 6 ODW drops to obtain soundings outside the convection in the inflow near the areas of interest. The aircraft should loiter in the eye or any other suitable area when it is necessary to service equipm ent.

There are THREE options associated with this experiment:

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