RESEARCH
My main research interest is in stratiform cloud processes, their climate impact, and their representation in large-scale (forecast, reanalysis, and climate) models, with polar cloud specialty. Cloud-induced forcings have potential implications for polar amplification and accelerated ice loss, which could have catastrophic consequences worldwide due to sea-level rise and changes in atmospheric circulation patterns. According to the IPCC report from 2021, cloud influence over the atmosphere is still the highest source of uncertainty in climate models, which are trying to provide reliable predictions of future climate. This uncertainty stems from incomplete knowledge of the processes happening in clouds and deficient representation of hydrometeors and cloud processes in models. My current research deals with these sources of uncertainty:
Stratiform Cloud Processes
The formation and persistence of stratiform clouds rely on a delicate balance of interactions between the microphysics (for example, aerosol-cloud interactions), macrophysics, small and large-scale dynamics, and the radiation budget. My goal is to examine and evaluate the sensitivity and importance of some of these processes in different cloud regimes, by using satellite and ground-based measurements from various deployments, reanalysis data products, and model simulations. I currently study different stages in the lifecycle of polar stratiform clouds and am also interested in examining cloud layering, surface radiative forcing, ice habit vapor growth effects on liquid-bearing cloud occurrence, and precipitation processes.
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Large-Scale Model Evaluation
The limited spatial and temporal resolutions of large-scale models impact the representation of cloud processes. In the macro and micro-physics schemes used by these models, some cloud processes are resolved, while others are diagnosed, often due to computational efficiency constraints. These modeling limitations and our incomplete understanding of stratiform cloud processes all result in model errors and biases. These errors and biases must be characterized in order to ultimately increase the reliability of weather and climate predictions by these models. I am interested in the evaluation of these model biases, that is, the assessment of the performance of various microphysics schemes using various tuning parameters, and the analysis of surface and top-of-atmosphere radiation errors stemming from these biases by using both bulk statistics and a case study approach, with the support of instrument simulators.
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Retrievals of Cloud Microphysical Properties
Observational data gaps ensuing from remote-sensing instrument characteristics and limitations impact the evaluation of modeling results and our pursuit of a comprehensive understanding of cloud processes. In addition to the operation of forward simulators at bridging such knowledge gaps, an active field of study involves the detection and retrieval of cloud thermodynamic properties and processes using radars and lidars. In the case of radars, for instance, signals are able to penetrate deep into clouds, and hence, encompass a high potential for revealing valuable information, which could greatly benefit Arctic, Antarctic, and Southern Ocean studies. Among other related research objectives, I am interested in the analysis of embedded liquid-bearing cloud layer detectability in polar clouds and the development of reliable methods for phase classification in some types of scenarios, using zenith-pointing radars.
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Mid-to-Upper Atmospheric Aeronomy (Ph.D. research)
The ionospheric D-region (~60 km up to ~95 km) and the corresponding neutral atmosphere, often referred to as the mesosphere-lower-thermosphere (MLT) are strongly tied through their physics and chemistry. The understanding of these processes in this part of the atmosphere is highly important mainly for radio wave propagation and communication, but also for GPS navigation, and long-term trajectories of satellites (due to atmospheric drag at their flight altitudes). The intense cooling of the upper atmosphere by anthropogenic greenhouse gases' emissions requires long-term monitoring of this region as well.
During my Ph.D. studies at Tel-Aviv University, I operated and analyzed measurements from very low frequencies (VLF; 3-30 kHz) electromagnetic wave receivers and ground-based infrared spectrometers, in order to study this part of the atmosphere in different regions of the world and on different time scales (from seconds up to several years). I detected a link between radio wave attenuation and the neutral atmosphere's temperature, as well as a clear semi-annual oscillation in the ionospheric D-region. In addition, I characterized the variations in mesopause temperatures above the Eastern Mediterranean and performed an analysis of waves propagating into the MLT from the troposphere.
A graphic user interface I created to view. process, and analyze radar, lidar, sounding, and other ancillary measurements.
Various sources of perturbations in the ionosphere and Mesosphere-lower-thermosphere reviewed in Silber et al. (2017; illustration courtesy of Maayan Visuals).
Lidar (a, b) and radar (c) measurements, wavelet analysis (d-e), and microwave radiometer retrievals (f) used to examine a highly supercooled drizzling cloud event reported in Silber et al. (2019).
Comparison of relative humidity with respect to ice between West Antarctic observations, AMPS (forecast model), and ERA5 (reanalysis model) discussed in Silber et al. (2019).