The Experts below are selected from a list of 219 Experts worldwide ranked by ideXlab platform

I. Koren - One of the best experts on this subject based on the ideXlab platform.

D. Rosenfeld - One of the best experts on this subject based on the ideXlab platform.

Y. J. Kaufman - One of the best experts on this subject based on the ideXlab platform.

Ilan Koren - One of the best experts on this subject based on the ideXlab platform.

  • switching cloud cover and dynamical regimes from open to closed Benard Cells in response to the suppression of precipitation by aerosols
    Atmospheric Chemistry and Physics, 2006
    Co-Authors: Daniel Rosenfeld, Yoram J Kaufman, Ilan Koren
    Abstract:

    The dynamic structure of the weakly sheared atmospheric marine boundary layer (MBL) supports three distinct states of cloud cover, which are associated with the concentrations of cloud condensation nuclei (CCN) aerosols in the MBL: (i) CCN rich MBL with closed Benard cellular convection that forms nearly full cloud cover; (ii) CCN depleted MBL with open cellular convection that forms <40% cloud cover; and, (iii) CCN starved MBL where clouds cannot form due to insufficient CCN, with near zero cloud cover. Here we propose a mechanism for the transition between these three states that involves the aerosol impacts on precipitation and the feedbacks on the dynamics of the clouds and on the aerosols deposition. By suppressing precipitation aerosols can reverse the direction of the airflow, converting the cloud structure from open to closed Cells and more than doubling the cloud cover. The three states possess positive feedbacks for self maintenance, so that small changes of the conditions can lead to bifurcation of the MBL cloud regime. The transition between the closed and open Cells occur at near pristine background level of aerosols, creating a large sensitivity of cloud radiative forcing to very small changes in aerosols at the MBL. The third state of super clean air can occur as the more efficient precipitation in cleaner air deposits the aerosols ever faster in a runaway positive feedback process. The proposed mechanism suggests that very small changes in the aerosols input to the MBL can have large impacts on the oceanic cloud cover and likely in turn on the global temperature, in ways that are not yet accounted for in the climate models.

Daniel Rosenfeld - One of the best experts on this subject based on the ideXlab platform.

  • Running Head: Radar Analysis of Cloud Systems
    2015
    Co-Authors: Yair Goldreich, Hanan Mozes, Daniel Rosenfeld, Prof Yair Goldreich
    Abstract:

    This study documents the climatological occurrence of rainfall contributed from different types of rain cloud systems over Israel and the adjacent sea. The rainy cloud types are: a. Cold front. b. Cloud systems that develop in the cold sector of the cyclones. c. Cloudiness of the cyclone center (vortex). The cloud systems within the cold sector include: a. Convection lines. b. Open Benard Cells and unorganized Cells. c. Coastal front. d. Cloud streets. While the warm front rain yield is negligible, the Red Sea trough adds about 5 % to the total precipitation in the Mediterranean climate region of the country. The main rainfall yield contribution in the north of the country comes from cold fronts and vortices while in the southern part is dominated by less dynamically and more air mass convection controlled rain cloud systems, such as Benard Cells and coastal front. Analysis of the cloud pattern on a monthly basis reveals that the cold front is more active during November-December and the main vortex activity starts in January, with the climax of the coastal front in December. We checked rainy/dry year variations and found that during rainy years, the vortex rain contribution is larger than that of the cold front. The coastal front also contributes more rain during wet years and tends to follow a more southerly route. In dry years, the proportion of vortex/cold front is reversed, and the coastal front rain yield is meager and has a more northerly route.- 3

  • switching cloud cover and dynamical regimes from open to closed Benard Cells in response to the suppression of precipitation by aerosols
    Atmospheric Chemistry and Physics, 2006
    Co-Authors: Daniel Rosenfeld, Yoram J Kaufman, Ilan Koren
    Abstract:

    The dynamic structure of the weakly sheared atmospheric marine boundary layer (MBL) supports three distinct states of cloud cover, which are associated with the concentrations of cloud condensation nuclei (CCN) aerosols in the MBL: (i) CCN rich MBL with closed Benard cellular convection that forms nearly full cloud cover; (ii) CCN depleted MBL with open cellular convection that forms <40% cloud cover; and, (iii) CCN starved MBL where clouds cannot form due to insufficient CCN, with near zero cloud cover. Here we propose a mechanism for the transition between these three states that involves the aerosol impacts on precipitation and the feedbacks on the dynamics of the clouds and on the aerosols deposition. By suppressing precipitation aerosols can reverse the direction of the airflow, converting the cloud structure from open to closed Cells and more than doubling the cloud cover. The three states possess positive feedbacks for self maintenance, so that small changes of the conditions can lead to bifurcation of the MBL cloud regime. The transition between the closed and open Cells occur at near pristine background level of aerosols, creating a large sensitivity of cloud radiative forcing to very small changes in aerosols at the MBL. The third state of super clean air can occur as the more efficient precipitation in cleaner air deposits the aerosols ever faster in a runaway positive feedback process. The proposed mechanism suggests that very small changes in the aerosols input to the MBL can have large impacts on the oceanic cloud cover and likely in turn on the global temperature, in ways that are not yet accounted for in the climate models.

  • Radar analysis of cloud systems and their rainfall yield in Israel
    Israel Journal of Earth Sciences, 2004
    Co-Authors: Yair Goldreich, Hanan Mozes, Daniel Rosenfeld
    Abstract:

    This study documents the climatological occurrence of rainfall contributed from different types of rain cloud systems over Israel and the adjacent sea. The rainy cloud types are: a. Cold front. b. Cloud systems that develop in the cold sector of the cyclones. c. Cloudiness of the cyclone center (vortex). The cloud systems within the cold sector include: a. Convection lines. b. Open Benard Cells and unorganized Cells. c. Coastal front. d. Cloud streets. While the warm front rain yield is negligible, the Red Sea trough adds about 5% to the total precipitation in the Mediterranean climate region of the country. The main rainfall yield contribution in the north of the country comes from cold fronts and vortices while in the southern part is dominated by less dynamically and more air mass convection controlled rain cloud systems, such as Benard Cells and coastal front. Analysis of the cloud pattern on a monthly basis reveals that the cold front is more active during November-December and the main vortex activity starts in January, with the climax of the coastal front in December. We checked rainy/dry year variations and found that during rainy years, the vortex rain contribution is larger than that of the cold front. The coastal front also contributes more rain during wet years and tends to follow a more southerly route. In dry years, the proportion of vortex/cold front is reversed, and the coastal front rain yield is meager and has a more northerly route.