Sensitivity of satellite observations for freshly produced lightning NOx S. Beirle1, M. Salzmann2, M. G. Lawrence1, and T. Wagner1 1Max-Planck-Institut für Chemie, (Otto Hahn Institute), Mainz, Germany 2Atmospheric and Oceanic Sciences Program, Princeton University, Princeton, NJ, USA
Abstract. In this study, we analyse the sensitivity of nadir viewing satellite
observations in the visible range to freshly produced lightning NOx.
This is a particular challenge due to the complex and highly variable conditions
of meteorology, (photo-) chemistry, and radiative transfer in and around
cumulonimbus clouds. For the first time, such a study is performed
accounting for photo-chemistry, dynamics, and radiative transfer in a
consistent way: A one week episode in the TOGA COARE/CEPEX region (Pacific)
in December 1992 is simulated with a 3-D cloud resolving chemistry model. The
simulated hydrometeor mixing ratios are fed into a Monte Carlo radiative
transfer model to calculate box-Air Mass Factors (box-AMFs) for NO2.
From these box-AMFs, together with model NOx profiles, slant columns of
NO2 (SNO2), i.e. synthetic satellite measurements, are calculated
and set in relation to the actual model NOx vertical column
(VNOx), yielding the "sensitivity" SNO2/VNOx.
From this study, we find a mean sensitivity of 0.46. NOx below the
cloud bottom is mostly present as NO2, but shielded from the
satellites' view, whereas NOx at the cloud top or above is shifted to
NO due to high photolysis and low temperature, and hence not detectable from
space. However, a significant fraction of the lightning produced NOx in the
middle part of the cloud is present as NO2 and has a good visibility
from space. Due to the resulting total sensitivity being quite high, nadir
viewing satellites provide a valuable additional platform to quantify
NOx production by lightning; strong lightning events over "clean"
regions should be clearly detectable in satellite observations. Since the
observed enhancement of NO2 column densities over mesoscale convective
systems are lower than expected for current estimates of NOx production
per flash, satellite measurements can in particular constrain the upper
bound of lightning NOx production estimates.
Citation: Beirle, S., Salzmann, M., Lawrence, M. G., and Wagner, T.: Sensitivity of satellite observations for freshly produced lightning NOx, Atmos. Chem. Phys., 9, 1077-1094, doi:10.5194/acp-9-1077-2009, 2009.