Investigation of High-Latitude Tracer Characteristics by using Ilas and other Satellite Data
Wookap Choi and Sumi Kim
Department of Atmospheric Sciences
Seoul National University
Seoul, 151-742,Korea
1. Introduction
Observing the chemical species in the stratosphere is crucial for understanding the procedures determining the distribution and change of the ozone layer. The Upper Atmosphere Research Satellite (UARS) was launched in 1991 and observations by the instruments on the satellite have been contributing much to our knowledge about the stratosphere.The spatial coverage of observation by the UARS, however, is limited to the low-to-middle latitudes. In this point of view the Improved Limb Atmosphere Spectrometer (ILAS) aboard the satellite ADEOS (Advanced Earth Satellite Observation), which was launched on August 1996, is complementary to those instruments on the UARS since the ILAS observed the stratosphere in the high latitude region (Sasano et al., 1995). The Halogen Occulation Experiment (HALOE) is one of the instrument aboard the UARS and both ILAS and HALOE use the solar occultation technique. TO investigate transport of chemical tracers, we need to know distribution across the wide latitudinal ranges. The instrument ILAS and HALOE thus are useful to investigate the temporal change of tracer distributions.
In this study distribution of ozone and methane in the stratosphere from
November 1997 to June 1998 were investigated by analyzing the ILAS (Version 3.1) and HALOE data (Version 18). The ILAS observes the high latitude region while the HALOE observes mainly low to middle latitudes. These observations were irregular in time and space. They were then interpolated in time and space to produce distribution on the regular grid points. The characteristic features appeared in the high latitudes are discussed.
2. Intercomparison of ILAS and HALOE vertical profiles
Among the chemical species observed by the ILAS we concentrated on methane and ozone distributions which are also observed by the HALOE. The ILAS data were available now in version 3.1 for 8 months from November 1996. The latitudes of observation by ILAS is shown in Fig. 1. The high - latitude coverage by ILAS is excellent. The HALOE data are now supplied in version 18 and the levels of accuracy are seemed to be high.At one point the vertical profiles from the ILAS and the HALOE are compared which are shown in Fig 2. The latitude (near 690S) and the longitude (near 1470E) of observation on the 20th of November are close enough for intercomparison. The vertical profiles of both tracers by both instruments are in good agreement although the ILAS shows smaller ozone mixing ratio than HALOE.
Fig. 1 Latitudes of observation by ILAS and Haloe for both sunset and sunrise
observations. The latitudinal range of observation by MLS is also shown.
Fig. 2 Vertical profiles of mixing ratios of (a) methane and (b) ozone from ILAS and HALOE.
Further intercomparison between two instrument are found in Lee et al. (1998). The ozone profile by ILAS was also compared to that of Microwave Limb Sounder (MLS) which is another instrument aboard UARS (Fig. 3). The shape of MLS is usually smoother than that of ILAS or HALOE. The profiles are similar in many respects.
Fig. 3 Vertical profiles of mixing ratios of ozone from ILAS and MLS.
(a) HALOE O3 Mixing Ratio (ppmv) (02/19/1997-03/23/1997)
(b) HALOE & ILAS 03 Mixing Ratio (ppmv) (02/19/1997-03/23/1997)
Fig. 4 Mixing ratio of ozone from (a) HALOE and (b) both ILAS and HALOE
The latitude coverage is revealed clearly in Figs. 3 and 4 which are latitude-altitude cross-sections. The upper panels show only HALOE data and bottom panels both HALOE and ILAS. The time of observation is not identical and dependent on the latitude as shown in Fig. 1. Although the latitude coverage by ILAS is not extensive its usefulness is clear. Especially for methane the Antarctic maxima below 30 km level is not anticipated from HALOE observation(Fig. 4a).Also the number of HALOE observation is too small to verify a certain pattern of distribution poleward of 50 degrees.
