Search Results

You are looking at 1 - 3 of 3 items for :

  • Author or Editor: Ian M. Brooks x
  • Journal of the Atmospheric Sciences x
  • Refine by Access: All Content x
Clear All Modify Search
Ian M. Brooks
and
David P. Rogers

Abstract

Large-scale horizontal rolls can have a significant influence on turbulent transport across the atmospheric boundary layer. The formation and maintenance of such rolls is dependent on the thermal and dynamic stability of the boundary layer (BL). The authors present aircraft observations of boundary layers, both with and without roll circulations, off the coast of California. The contribution of the rolls to the turbulent fluxes of heat, moisture, and momentum, and the variances of the three velocity components are determined for four cases. The fractional roll contributions to the u and w variances, and the sensible heat and along-wind momentum fluxes, show a near linear increase with altitude, from less than 10% at 30 m to more than 70% at the top of the BL. The variance in υ and crosswind momentum flux are more scattered, although the variance shows a slight increase with altitude from about 40% to 60%. The latent heat flux also shows a great deal of scatter, especially in the lower third of the BL where the total flux is small; above this, values range between about 40% and 85% but show no clear trends. A stability parameter in the form of a bulk Richardson Ri number is calculated for each of 13 profiles through the boundary layer; it is found that the Richardson number successfully identifies those cases where rolls are present, and its value corresponds to some extent with the strength of the rolls. Values close to zero correspond to cases with well-defined rolls; for 0.1 < Ri < 0.25 rolls are found to exist, but they tend to be weak and patchy; and no rolls are found where Ri is greater than the critical value of approximately 0.25. Reynolds numbers are calculated from a number of different definitions and indicate the dynamic instability of the shear dominated boundary layers.

Full access
Kevin J. Noone
,
Elisabeth Öström
,
Ronald J. Ferek
,
Tim Garrett
,
Peter V. Hobbs
,
Doug W. Johnson
,
Jonathan P. Taylor
,
Lynn M. Russell
,
Richard C. Flagan
,
John H. Seinfeld
,
Colin D. O’Dowd
,
Michael H. Smith
,
Philip A. Durkee
,
Kurt Nielsen
,
James G. Hudson
,
Robert A. Pockalny
,
Lieve De Bock
,
René E. Van Grieken
,
Richard F. Gasparovic
, and
Ian Brooks

Abstract

The effects of anthropogenic particulate emissions from ships on the radiative, microphysical, and chemical properties of moderately polluted marine stratiform clouds are examined. A case study of two ships in the same air mass is presented where one of the vessels caused a discernible ship track while the other did not. In situ measurements of cloud droplet size distributions, liquid water content, and cloud radiative properties, as well as aerosol size distributions (outside cloud, interstitial, and cloud droplet residual particles) and aerosol chemistry, are presented. These are related to measurements of cloud radiative properties. The differences between the aerosol in the two ship plumes are discussed;these indicate that combustion-derived particles in the size range of about 0.03–0.3-μm radius were those that caused the microphysical changes in the clouds that were responsible for the ship track.

The authors examine the processes behind ship track formation in a moderately polluted marine boundary layer as an example of the effects that anthropogenic particulate pollution can have in the albedo of marine stratiform clouds.

Full access
Kevin J. Noone
,
Doug W. Johnson
,
Jonathan P. Taylor
,
Ronald J. Ferek
,
Tim Garrett
,
Peter V. Hobbs
,
Philip A. Durkee
,
Kurt Nielsen
,
Elisabeth Öström
,
Colin O’Dowd
,
Michael H. Smith
,
Lynn M. Russell
,
Richard C. Flagan
,
John H. Seinfeld
,
Lieve De Bock
,
René E. Van Grieken
,
James G. Hudson
,
Ian Brooks
,
Richard F. Gasparovic
, and
Robert A. Pockalny

Abstract

A case study of the effects of ship emissions on the microphysical, radiative, and chemical properties of polluted marine boundary layer clouds is presented. Two ship tracks are discussed in detail. In situ measurements of cloud drop size distributions, liquid water content, and cloud radiative properties, as well as aerosol size distributions (outside-cloud, interstitial, and cloud droplet residual particles) and aerosol chemistry, are presented. These are related to remotely sensed measurements of cloud radiative properties.

The authors examine the processes behind ship track formation in a polluted marine boundary layer as an example of the effects of anthropogenic particulate pollution on the albedo of marine stratiform clouds.

Full access