VOLUME 1 - E-Library - WMO

(3)Angstrom's turbidity coefficient J} is computed from(3 = 't'AA.A Cl(4)which is derived from (2).The following discussion is designed to help the reader interpret the data in this report. Moredetailed information can be gained from the list of references provided at the end of the text.a (ALPHA), the wavelength exponent, is related to the size distribution of the particlesconstituting the aerosol. Its average value is about 1.3. Large values of a indicate arelatively higher ratio of small particles to large particles (large particles have radii> 0.5microns).The particle number density (m-4) is defined as:n (r)dN(r)drand(5)n (r o ) is the particle number density at an arbitrary fixed particle radius r o ' e.g., r o = 1 lJ.m.r is the particle radius of the measured aerosol.For the purposes of this report, a is independent of wavelength. a has a range of about 0 to4 but generally it is within the range of 0.5 to 2.5. Negative alpha values may appear in thisreport. These are thought to be associated with anomalous particle distributions but mayoccasionally be noise introduced by limits in instrumental accuracy when 't'AA.I - 't' AA.2'(3 (BETA), the turbidity coefficient defined in equation (4) above, is computed usingwavelength, but is actually independent of A because of the "canceling" effect of 't' AA. whichis wavelength dependent. (3 0.2 asrelatively hazy for near sea level readings.Data Tables DescriptionData in this edition are presented in a new form which ·conserves space and allows for thepublication of aerosol optical depth in one to four wavelength regions. Data: are presented forstations listed by ascending NCDC number. Delayed data are presented under the stationI-ii