Principal Investigator: Richard Bevilacqua (bevilacqua@nrl.navy.mil)
The US Naval Research Laboratory's space-based POAM measurement program consists of 2 instruments, the Polar Ozone and Aerosol Measurement (POAM ) II which operated from Oct. 1993 to Nov. 1996, and POAM III which was launched in March 1998 and is still operational. Below we describe both the POAM II and POAM III missions. Overview of POAM mission
POAM II
The Polar Ozone and Aerosol Measurement (POAM II) was a nine-channel visible/near infrared photometer (352-1060 nm) for measuring trace constituents in the stratosphere using the solar occultation technique. The instrument is described in detail by Glaccum et al. [1996]. POAM II was launched on September 26, 1993 into a sun-synchronous 98.7E inclination orbit, and measurements were obtained until the SPOT 3 satellite malfunctioned on November 14, 1996. The POAM II Version 5 retrieval algorithm is described by Lumpe et al. [1997], and this work also includes a retrieval error analysis. The ozone measurements are validated by Deniel et al. [1997] and Rusch et al. [1997]. An analysis of POAM II measurements in the ozone hole is given in Bevilacqua et al. [1997]. An overview of POAM II NO2 data, including comparisons with coincident HALOE data, is given by Randall et al. [1998]. An overview of the aerosol extinction measurements is given in Randall et al. [1996], and a detailed POAM II/SAGE II aerosol extinction comparison study is given in Randall et al. [1999]. The POAM II PSC detection methodology and a Southern Hemisphere climatology are presented in Fromm et al. [1997], and the POAM Northern Hemisphere PSC climatology is given in Fromm et al. [1999]. The POAM PSC observations have been compared to microphysical model calculations along isentropic parcel trajectories in Steele et al. [1999].
POAM III
POAM III was launched on the SPOT 4 spacecraft on 24 March, 1998, in an orbit (and thus measurement coverage) nearly identical to that of POAM II, and is now in routine operation. The POAM III instrument is very similar in design and operation to POAM II, but has been substantially improved in several areas. Among the most important of these is a large increase in the measurement signal-to-noise (especially in the three bluest channels), and greater sun tracker sensitivity enabling measurements to be made (in cloud free conditions) well into the troposphere. The POAM III measurement complement includes ozone, water vapor (which was not provided with POAM II), NO2, and aerosol extinction. The table below gives the POAM III channel wavelength placements and purpose, and Table 2 give the current measurement complement and approximate altitude ranges. A more detailed description of the POAM III instrument, and early validation results is given by Lucke at al. [1999]. Version 2 is the current retrieval version, and the POAM III data are publicly available through the POAM web page.
The POAM III instrument makes 14 measurements per day in each hemisphere around a circle of latitude, and the latitude of the observations varies with an approximately semi-annual period. In Figure 1 we show the latitude of the POAM III measurements in the northern hemisphere winter. We also show the equivalent latitude of the measurements on the 500 K potential temperature surface, and the vortex edge value obtained using the Nash et al. [1996] vortex edge analysis. In the Northern Hemisphere, POAM measurements are obtained both inside and outside the vortex on a daily basis throughout the winter. Although the details of this measurement coverage change from year-to-year, Figure 1 is representative of the coverage in all years of POAM II and POAM III measurement years.
POAM III channels:
Channel Center Wavelength Width Primary Use
------- ----------------- ----- -------------------
1 353.4(nm) 9.70(nm) Rayleigh scattering
2 439.7 2.07 NO2 on
3 442.3 2.05 NO2 off
4 603.4 17.7 Ozone
5 761.3 2.25 O2 on
6 779.4 10.1 O2 off, Aerosol
7 922.4 2.56 H2O off, Aerosol
8 935.8 2.59 H2O on
9 1018.5 11.5 Aerosol
As can be seen from Figure 1, during the SOLVE campaign the POAM measurement latitude varies from a maximum of 67.4 degrees in November and again in March, to a minimum of 63.5 degrees at the end of December . Thus, the POAM measurements will be obtained within about 4.5 degrees from the Kiruna field site throughout the mission. This makes POAM ideally suited for the SOLVE campaign. POAM participation in the SOLVE Program
POAM participation in SOLVE will include , first of all, participation in validation opportunities with measurements obtained in the three components of the SOLVE campaign (high altitude balloons, DC-8, and ER2). Secondly, we plan to participate on-site during the SOLVE ER-2 field campaigns, and make the POAM III data available on a daily basis to the SOLVE science team. Finally, we will infer ozone loss for the 1999-2000 winter using the POAM III data and the REPROBUS CTM (Chemical-Transport Model) using the techniques described in Deniel et al (1998), and make detailed comparisons with the results obtained in other SOLVE measurement/model investigations. These types of comparisons should provide valuable insights into current problems and uncertainties in inferring ozone loss using satellite measurements and global models.
During the SOLVE mission, we anticipate that POAM III retrievals will be made available about every 12 hours, with the most current data being approximately 4-6 hours old. The retrieval data will be placed in the SOLVE database. The altitude ranges for the species provided to SOLVE will be: 10-60 km for ozone, 20-40 km for NO2, 5-45 km for water vapor, and 5-30 km for aerosol extinction. Other data files such as a PSC catalog, daily PSC display maps, and various plots will be made available on the POAM-SOLVE web site, and at Kiruna during the ER2 deployments. Requests for specific types of data or plots from other SOLVE participants are welcome. Such requests should be directed to Richard Bevilacqua (bevilacqua@nrl.navy.mil).
The SOLVE mission provides a unique opportunity for validating the POAM data. We are particularly interested in performing detailed validations of the POAM III upper tropospheric and lower stratospheric water vapor retrievals. In addition, we hope to evaluate the aerosol products including extinction (in clear air and in clouds), and the inferred surface area and volume density, especially in PSCs.
Figure 1. POAM III northern hemisphere equivalent latitude sampling for the 1998-1999 winter. The red line is the measurement latitude. The blue symbols are the equivalent latitude values. The green line is the polar vortex edge.