Research Topics

Atmospheric Electricity
This field of research deals with fair-weather electricity.  By this we mean electricity measured in the atmosphere when no thunderstorms are active in the surrounding region.  This electricity is generally related to global thunderstorms which produce electric currents flowing in the atmosphere between the ionosphere and the earth.  In particular, I am interested in the AC fields produced by global lightning in the ELF range, known as the Schumann resonance.   However, we have also started recently to measure the DC conduction currents in the atmosphere  due to  global thunderstorm activity.  We are also interested in knowing how many thunderstorms actually drive the global circuit, and if they are changing due to climate change.
Lightning activity in thunderstorms is closely related to the microphysics of clouds and storm dynamics. The storms with large amounts of lightning are often also very destructive, having large hail, strong winds, and excessive rainfall.  These storms are often the cause of flash floods, which are often observed in the southern parts of Israel.  We are researching the connections between lightning activity, rainfall and severe weather in a number of locations around the world.   See the FLASH project website.  In addition, we are studying the link between lightning activity in hurricanes, and the intensification of these storms.

Sprites are a phenomenon discovered in the upper atmosphere in 1989.  They are optical flashes of light that occur far above thunderstorms (50-100 km altitude), but are associated with a specific type of intense lightning in the storm below (positive lightning).  The strong flashes that produce the sprites also produce strong radio signals that we can easily detect in Israel, even if the storm occurs in the United States. We perform regular ground-based observations of sprites in the winter thunderstorm season in Israel.  In addition, we are working on laboratory experiments to investigate the possibility of sprites existing on other planets.

Global Climate Change
There is strong evidence that the Earth's temperatures are warming, and that this warming is caused in large part by anthropogenic activity on our planet.  Changes in greenhouse gases over the next 50 years are expected to result in major climate changes on a global scale, and perhaps also here in Israel.  We are studying how the climate in Israel has changed over the last 50-100 years, while trying to predict possible future changes to the region's climate.  We are particularly interested in the impact of climate change on thunderstorms and severe weather (both regionally and globally).  In addition, we have started monitoring the upper atmospheric temperatures above Israel (~90km) to study climate changes in the mesopause region.
Tropospheric Chemistry
One of the most important greenhouse gases is Ozone.  The ozone in the lower atmosphere is "bad" ozone since it traps heat emitted from the earth, enhancing the greenhouse effect.  The ozone in the upper atmopshere is "good" ozone, since it blocks out the harmful UV radiation from the sun.  One of the main precursors for ozone formation in the lower atmosphere is NOx (nitrogen oxides), and lightning is one of the major natural sources of NOx.  If the climate changes, and thunderstorm distribution and frequency change, this may imply feedbacks on tropospheric ozone.

El Nino
El Nino became a household name in 1997, but has been studied by scientist for decades.  The El Nino phenomenon is the result of the warming of the tropical eastern Pacific Ocean which lasts for 6-18 months.  This warming occurs every few years and results in the disruption of global weather patterns.  In Israel we have found that the El Nino cycle affects the amount of winter rainfall, however this link occurs only since the 1970s. We're not sure why.  Generally, during El Nino years we get above average rainfall in Israel, while drought years are often associated with La Nina years.

Biomass Burning
Lightning is a major cause of wildfires in the mid- to high liatitudes.  Natural fires depend on the regional and perhaps global climate conditions, the availability of  fuel (vegetation) and the amount of lightning.  Our studies have shown that natural fires may increase dramatically in the future due to global warming.  Furthermore, global biomass burning is likely contributing to the increase in greenhouse gases in the atmosphere.  We have also recently shown that aerosols from fires can influence the cloud microphysics and dynamics, with feedbacks on the lightning activity in regions of biomass burning.

For more than a century people have claimed hearing sounds when seeing large shooting stars in the sky.  It is impossible for the sound waves to be produced by the meteor since sound travels much slower than light.  The only explanation is that the meteor produces radio waves (similar to lightning) that reach the observer with the light, and are then transformed to audible sound in vibrating objects close to the observer. We have carried out research searching for these electrophonic sounds from meteors.  At the same time we discovered that during meteor showers, the ionospheric properties get changed due to the ions and meteoric dust deposited in the upper atmosphere.

In recent years a number of groups around the globe have measured (at first by accident) high levels of ultra low frequency (ULF) radio waves in the atmosphere close to the epicenter of earthquakes, weeks and even months prior to the earthquakes.  It is not clear the source of these radio waves, but this provides hope that one day we may be able to predict earthquakes.  Using equipment we normally use to study Atmospheric Electricity we are trying to detect these earthquake precursors along the Dead Sea Rift Valley.  We have 3 ULF station continuously monitoring the environment in that seismic region.
   Space Weather
Space Weather is a new field of research looking at the interaction between solar storms and the terrestrial environment.  How do solar flares, X-rays, coronal mass ejections (CMEs) impact the Eath's magnetosphere, ionosphere, and atmosphere?  One was of studying these effects is by studying the changes in the Earth-ionosphere waveguide, formed by the conductive Earth surface and the conductive ionosphere at 60-100km altitutde.  Changes in the conductivity and hence reflection height of the lower ionosphere can be detected in our ground-based ELF/VLF measurements, and translated into physical changes in the upper atmosphere, lower ionosphere.