Engineering topics

Celarier, E.

Publications and source records attributed to Celarier, E..

4 records

NASA NTRS2007

The 'Weekend Effect' in Tropospheric NO2 Seen from the Ozone Monitoring Instrument

The Ozone Monitoring Instrument has gathered daily global data on NO2 and other atmospheric trace gases since its launch on the EOS Aura satellite in 2004. The large accumulated data set makes it possible to monitor changes of both meteorological and anthropogenic origin in tropospheric NOz amounts. In particular, averages on time scales on the order of a year show a distinct 'weekend effect' in NO2 variation, with smaller NO2 amounts seen on Saturday and/or Sunday than on the remaining weekdays. Using the OMI NO2 Standard Product (SP), we examine this effect in relation to geopolitical boundaries and investigate implications for identifying sources. We also use the SP data to find evidence for other short-term anthropogenic changes in NO2 emissions over heavily polluted regions including the United States, Europe and China.

Bucsela, E.↗

NASA NTRS2000

UV 380 nm Reflectivity of the Earth's Surface

The 380 nm radiance measurements of TOMS (Total Ozone Mapping Spectrometer) have been converted into a global data set of daily (1979 to 1992) Lambert equivalent reflectivities R of the Earth's surface and boundary layer (clouds, aerosols, surface haze, and snow/ice). Since UV surface reflectivity is between 2 and 8% for both land and water during all seasons of the year (except for ice and snow cover), reflectivities larger than the surface value indicates the presence of clouds, haze, or aerosols in the satellite field of view. Statistical analysis of 14 years of daily data show that most snow/ice-free regions of the Earth have their largest fraction of days each year when the reflectivity is low (R less than 10%). The 380 nm reflectivity data shows that the true surface reflectivity is 2 to 3% lower than the most frequently occurring reflectivity value for each TOMS scene. The most likely cause of this could be a combination of frequently occurring boundary-layer water or aerosol haze. For most regions, the observation of extremely clear conditions needed to estimate the surface reflectivity from space is a comparatively rare occurrence. Certain areas (e.g., Australia, southern Africa, portions of northern Africa) are cloud-free more than 80% of the year, which exposes these regions to larger amounts of UV radiation than at comparable latitudes in the Northern Hemisphere. Regions over rain-forests, jungle areas, Europe and Russia, the bands surrounding the Arctic and Antarctic regions, and many ocean areas have significant cloud cover (R greater than 15%) more than half of each year. In the low to middle latitudes, the areas with the heaviest cloud cover (highest reflectivity for most of the year) are the forest areas of northern South America, southern Central America, the jungle areas of equatorial Africa, and high mountain regions such as the Himalayas or the Andes. The TOMS reflectivity data show the presence of large nearly clear ocean areas and the effects of the major ocean currents on cloud production.

Herman, J. R.↗

NASA NTRS1999

Interannual Variability of Ozone and Ultraviolet Exposure

Annual zonal averages of ozone amounts from Nimbus-7/TOMS (Total Ozone Mapping Spectrometer) (1979 to 1992) are used to estimate the interannual variability of ozone and UVB (290 - 315 nm) irradiance between plus or minus 60 deg. latitude. Clear-sky interannual ozone and UVB changes are mainly caused by the Quasi Biennial Oscillation (QBO) of stratospheric winds, and can amount to plus or minus 15% at 300 nm and plus or minus 5% at 310 nm (or erythemal irradiance) at the equator and at middle latitudes. Near the equator, the interannual variability of ozone amounts and UV irradiance caused by the combination of the 2.3 year QBO and annual cycles implies that there is about a 5-year periodicity in UVB variability. At higher latitudes, the appearance of the interannual UVB maximum is predicted by the QBO, but without the regular periodicity. The 5-year periodic QBO effects on UVB irradiance are larger than the currently evaluated long-term changes caused by the decrease in ozone amounts.

Herman, J. R.↗

NASA NTRS1998

Estimates of Spectral UV Irradiance from Earth Probe TOMS: Comparisons with Ground-Based Measurements

Estimates of the spectral UV flux incident on the Earth's surface are calculated based on total column ozone and cloud optical thickness determined from the Earth Probe Total Ozone Mapping Spectrometer (TOMS) satellite data. Spectral fluxes are calculated between 300 and 325 nanometers using a weighting function similar to the measured function of the Brewer Spectrophotometer. Comparisons of the TOMS-derived values with ground-based Brewer Spectrophotometer measurements at 3 locations from the Canadian Brewer network (Toronto, Saskatoon and Saturna Island) and 3 locations from the United States EPA network (Boston, Gaithersburg, and Boulder) show reasonably good agreement over a variety of clear and cloudy conditions. Some systematic differences are apparent, particularly when snow/ice is present and the TOMS instrument cannot distinguish between clouds and snow covered ground, thus leading to an underestimation of UV flux. The presence of absorbing aerosols near the ground or sub-pixel clouds can also lead to significant errors. There are also possible errors in the Brewer data due to radiometric calibration uncertainties and uncorrected cosine response.

Labow, G. J.↗