Comment on essd-2022-272

Abstract

<strong class="journal-contentHeaderColor">Abstract.</strong> We report the recovery and re-calibration of an extensive dataset of vertical profile measurements of the 1963/64 stratospheric aerosol layer measured from a two-site searchlight measurement facility at White Sands missile base and Sacramento Peak observatory, in New Mexico, US. The recovered dataset comprises 105 profiles of 550 nm aerosol extinction (&beta;<em>_p</em> (<em>z</em>)) and is part of a longer program of measurements with the US Air Force Cambridge Research Laboratories (AFCRL) searchlight facility that began in February 1963. The recovered series of &beta;<em>_p</em> (<em>z</em>) profiles span the 13-month period December 1963 to December 1964 and provide a unique record of the altitude and vertical extent of the Northern Hemisphere dispersed portion of the aerosol cloud from the March 1963 Agung volcanic eruption. The data recovery methodology involved first re-digitizing the 105 original &beta;<em>_p</em> (<em>z</em>) profiles (&beta;<em>_p^Orig</em> (<em>z</em>)) from individual Figures within an AFCRL research report (Elterman, 1966a). The re-calibration involves inverting the original equation used to compute &beta;<em>_p</em> (<em>z</em>) in Elterman (1966a; 1966b) to retrieve a normalized detector response ((<em>E_rp (z)</em>)/(<em>E_rp</em> (35))) profile for each of the 105 re-digitized &beta;<em>_p^Orig</em> (<em>z</em>) profiles. An iterative procedure was then used to compute the re-calibration &beta;<em>_p^Orig</em> (<em>z</em>) profiles (&beta;<em>_p^Recal (z)</em>), with the molecular extinction profile calculated with the corresponding daily molecular extinction profile calculated from local soundings, rather than the US Standard Atmosphere 1962 in the original dataset. Two-way molecular and aerosol transmittance corrections are applied using the MODTRAN (MODerate resolution atmospheric TRANsmission) code in transmission mode, applying a best-estimate aerosol phase function calculated from measurements, applied for the entire 2.76 to 35.2 km column. For the tropospheric aerosol transmittance, the AERONET aerosol phase function from White Sands High Energy Laser Systems Test Facility (HELSTF) was applied (2.76 to 10.7 km), a separate stratospheric phase function applied between 11.2 and 35.2 km, calculated from a set of particle size distributions measured by the U-2 high-altitude aircraft over a US region in the vicinity of White Sands in early 1964. Errors were estimated taking as a reference the errors determined in the computation of &beta;<em>_p^Orig</em> (<em>z</em>). Using available tabulated data from the original procedure the errors in the re-digitalization of &beta;<em>_p^Orig</em> (<em>z</em>) and in the retrieval of the (<em>E_rp (z)</em>)/(<em>E_rp</em> (35)) procedures were calculated and later added to the original estimates. Both the &beta;<em>_p^Recal (z)</em> and the stratospheric aerosol optical depth magnitudes showed higher magnitudes than &beta;<em>_p^Orig</em> (<em>z</em>) and the original stratospheric aerosol optical depth, however their magnitudes show a reasonable agreement with other contemporary observations. Both the original and re-calibration datasets are being submitted to PANGAEA data repository for its storage and public access.