Introduction

A lidar operating at 532 nm wavelength was designed and constructed for stratospheric aerosol measurements at CMDL in Boulder, CO and first observed the stratospheric layer in August, 1999. Components of the lidar were tested at Mauna Loa Observatory (MLO) and compared to the MLO lidar (view comparison). The Boulder lidar uses many of the same components as the MLO lidar, the main difference being the much lower power laser used at Boulder.

Annual Cycle

The average Integrated Aerosol Backscatter (IABS, integrated above the tropopause) for the winter of 2000-2001 was 38% higher than the winter of 1999-2000. The IABS was significantly lower over MLO but the same increase of 38% was observed. The higher IABS over Boulder reflects the lower altitudes (higher densities) of the bulk of the aerosol compared to MLO. The small seasonal cycle in the MLO tropopause is seen to peak in winter, changing by only 1.5 km from the summer minimum. This is characteristic of the tropopause in tropical latitudes and is opposite the seasonal cycle at midlatitudes, which peak in summer....

2001 Asian Dust Episode

Springtime wind storms over high Chinese desert plateaus often load large amounts of particulates in the upper troposphere. The air is transported to the east picking up pollutants from industrialized areas and is advected out over the Pacific Ocean. The dust is regularly seen at Mauna Loa Observatory and in some years is seen over the continental U.S. The spring of 2001 saw unusually high amounts of Asian dust over much of the U.S. and the lidar recorded the vertical distribution of the dust on several nights. Seasonal averages are shown below for 2000 and 2001, followed by the individual profiles in March and April, 2001. The 2000 springtime average (AM 2000) is lower than any of the 2001profiles and may have been an unusually clear spring. March 2000 was not included in the average because the lidar was not recording the lower altitudes at that time. The profiles of 4/14, 4/15 and 4/24 show the dust reaching well up into the upper troposphere. The tropopause was between 11km and 13km for these profiles.

Addition of Channel 2

The first few months of measurements over Boulder indicated that the lower tropopause (compared to MLO) and greater scattering in the upper troposphere complicated the interpretation of the lower part of the stratospheric aerosol profile. It was determined that the dynamic range of the single detector channel could not accurately profile the aerosol backscatter over the entire altitude range of interest. A second, low altitude channel, for which the signal is attenuated, was added in April, 2000. This increased the altitude range covered and decreased the error in the Integrated Aerosol Backscatter (IABS) from 8.3% to 5.9%. Signals for the two channels are shown below. The signals are mainly from molecular scattering. Channel 2 is normally spliced onto channel 1 at 14km.