Atmospheric Radiative Transfer
I work with different scale models of the radiative transfer of solar radiation in the Earth's atmosphere. On the microscale, I build models that describe the interaction of solar radiation with particles and cloud drops in the Earth's atmosphere. I am particularly interested in the different effects of mixtures of sulfates, soot, organics, and dust. How can one best describe an inhomogeneous mixture of such components? What are the differing effects of soluble vs. insoluble components, liquids vs. solids, absorbing vs. nonabsorbing? What is the exact composition of organic aerosols and how much solar radiation do they absorb, if any?
The description of microscale radiative phenomena in larger scale models presents its own challenge. How can one represent subgrid scale features, such as inhomogeneous clouds and partial cloud cover, in such models?
Radiative Forcing of Climate
Models of various scales are also used to assess changes in the global balance of radiative flux in the Earth's atmosphere leading to changes in temperature and feedbacks on the hydrological cycle, dynamics, and other components of the climate system: Intergovernmental Panel on Climate Change. Based on the results of the microscale radiative transfer models, I look at how the presence of various types of particles affects the Earth's radiative-convective balance and feeds back on the Earth's general circulation. Which particles cause a warming and which cause a cooling, and how does this change with their global distribution? Do absorbing particles act to increase or decrease cloud amount, increase or decrease the strength of the Hadley circulation? Aerosol-Cloud Interactions and Absorbing Aerosols Inside and Outside of Clouds
Clouds are one of the most important influences the transfer of radiation through the Earth's atmosphere, the Earth's energy budget, and it's climate, and yet properly simulating cloud properties remains a challenge in models of all scales. Even predicting the number of drops a cloud will develop and the distribution of the sizes of those drops under given thermodynamic conditions is not a simple task. I work with parcel scale models of cloud microphysics to try to understand the processes that are important to the drop spectrum evolution. I want to be able to properly predict how large drops will grow given different compositions of particles that nucleate and mix with the drops. What causes the high concentrations of small drops observed in stratocumulus clouds? What mechanism allows the drops to grow to collision size? How much soot, organic material, and dust enters such drops? What is the real boundary between unactivated interstitial particles and small cloud drops, and how many of these unactivated particles remain in a given cloud layer?
While human beings only detect the intensity and wavelength of light, some species, both terrestrial and marine, are able to sense light's third attribute, polarization. Such species use polarization (the direction of the electric field) for different tasks such as orientation, navigation, prey detection, and communication. Under water, where the intensity signal is distorted by refraction and weakened by absorption, the ability to utilize polarization can be even more important than on land. For many years, theoretical models of polarized light under water were based on the theory of single scattering of the direct solar beam by small particles (Rayleigh scattering). Models accounting for scattering by larger particles (Mie scattering) have been approximate, and the most sophisticated models to date do not separate the effects of Mie scattering from effects of non-sphericity and multiple scattering. Furthermore, recent measurements under water reveal deviations from the polarization patterns predicted by models, in clear as well as semi-turbid waters. We are using a step-by-step approach to analyze the separate effects of particle size, particle size distribution, particle composition, particle shape, and varying orders of scattering on the underwater polarization pattern with a goal of identifying the processes at play in different water types.Underwater Polarization
At Hebrew University, we have initiated a laboratory for observing transient luminous events (TLE's), such as sprites, blue starters, jets, and ELVES, which occur above storm clouds. This complements the ongoing research at Tel Aviv University and The Open University. We have also built simple theoretical models to help explain some observed phenomena, such as the circular configuration of simultaneous sprites and the shift of the location of sprites from their parent lightning event. Transient Luminous Events