Overview

Turkey and southeast Europe have experienced severe drought and heat waves over the past several years. Istanbul, which is the largest and most populated urban area in that region, has been under extreme water shortage due to these regional climatic effects, extreme population growth, increased air pollution and increased demand for water. In the winter and spring of 2008, RAL conducted the Cloud and Aerosol Research in Istanbul program. Two 6–week intensive observation periods were planned between February 2008 and June 2008. Aerosol and cloud physics measurements were done with a research aircraft to characterize the properties of the aerosols and clouds in the region of Istanbul. The aircraft was equipped with instrumentation for the characterization of atmospheric constituents (gas and aerosols) and cloud particles in addition to measuring atmospheric dynamic and thermodynamic properties. A total of 92 flights with 350 flight hours were carried out during the project. The data analysis effort was completed in May 2009.

The results of this study provide a broad perspective on the cloud and precipitation formation processes in Istanbul. High aerosol loading resulting from air pollution in the region of Istanbul was measured, which may modify the physical properties of the cloud particles, increase the number concentration of cloud droplets, and inhibit the formation of large droplets by the collision–coalescence process. Aircraft measurements documented the high levels of pollution aerosols around the Istanbul area and the effect that these may have on the cloud droplet concentrations and size distributions. In some cases a cloud modification effect was measured that may be attributed to higher concentrations of aerosols when compared to an area with lower concentration of aerosols. Although this effect is not well understood, cloud modeling studies can be useful in understanding such complex cloud modification effects.

This work was conducted in collaboration with Seeding Operations and Atmospheric Research (SOAR) and Texas A&M University (TAMU).

Project Objectives

The 2008 Cloud and Aerosol Research in Istanbul program was aimed to study and analyze the potential benefits of weather modification in the area of Istanbul. The project provided a broad perspective on the feasibility and the effectiveness of weather modification as well as additional data for studying other atmospheric phenomena that are of high scientific research value such as regional global warming effects, heat island effects, aerosol loading and trace gas chemistry.

The following objectives were set for the project:

1. Determine a basic understanding of the natural cloud characteristics and precipitation processes occurring within the clouds of Istanbul, Turkey. Specifically, the natural microphysical characteristics of the warm and cold clouds will be documented. Natural and anthropogenic aerosols will be sampled to determine their effect on precipitation processes.
2. Conduct measurements of the physical chain of events that follow hygroscopic seeding of suitable Istanbul area clouds. Conduct measurements of the physical chain of events that follow glaciogenic seeding of suitable Istanbul area clouds using modern formulations of silver iodide.
3. Evaluate radar–derived rainfall from seeded clouds and unseeded clouds.
4. Conduct analysis of the data collected that determines the feasibility to design a multi–year cloud seeding operational and research program as a viable water management technology for the Istanbul Municipality.
5. Use of the airborne measurements as initial condition and calibration data for numerical simulations of cloud processes in order to analyze the effects of local air pollution and the seeding material on the amount of precipitation.

In order to achieve these objectives the SOAR, NCAR and TAMU scientists together with the sophisticated SOAR aircraft research platform were mobilized to Istanbul to conduct weather modification research and atmospheric measurements from January 2008 through June 2008.