Comparisons of seasonal and diurnal variations between CLARS and in situ
measurements
Clare Wong1, Dejian Fu1, Thomas Pongetti1, Sally Newman2, Eric Kort1, Riley Duren1, Charles Miller1,
Yuk L. Yung2, Stanley Sander1
1Jet
Propulsion Laboratory, California Institute of Technology, Pasadena, USA
Institute of Technology, Pasadena, USA
2California
Carbon dioxide (CO2) and methane (CH4) are long-lived greenhouse gases (GHGs)
that play crucial roles in climate change. The California Laboratory of Atmospheric
Remote Sensing (CLARS) on Mount Wilson provides temporal and spatial
measurements of CO2, CH4 and other chemical species in the Los Angeles basin,
tracks their emissions in the basin and at the same time serves as validation of
satellite measurements such as OCO-2. At CLARS, a Fourier Transform Spectrometer
(FTS), located at 1.7 km ASL, points downward at 29 different targets in the Los
Angeles basin to measure the slant column abundances of CO2, CH4, N2O, CO and O2
using reflected sunlight in the near-infrared region. This technique allows the
spatial coverage of the Los Angeles basin at different times of the day. In addition,
we measure column abundances above Mt. Wilson using a spectralon plate. Here we
present the comparisons of seasonal and diurnal variations between CLARS XGAS
and in situ data. The Spectralon XCO2 and XCO show similar seasonal variations
observed by flask measurement on Mt Wilson. Seasonal variations of Spectralon
XCH4 nevertheless show deviation from in situ data, due to the fluctuations of
tropopause height. The CLARS basin XCO2 and XCH4 showed significant diurnal
variability. A simple box model approach is used to calculate the average mixing
ratio of CO2 and CH4 along the CLARS geometric light path using in situ data in the
boundary layer and mixed layer height data from a ceilometer in Pasadena.
Comparisons show surprisingly good agreement on days when the boundary layer
is vertical well mixed. These comparisons validate the seasonal and diurnal
variations observed by the CLARS FTS yet aircraft data is required for calibration.
Copyright 2013. California Institute of Technology. Government sponsorship acknowledged.