Contributors:
- Angell, J.K. ERL/Air Resources Laboratory
- Gelman, M.E. NWS/Climate Prediction Center
- Hofmann, D. ERL/Climate Monitoring and Diagnostic Lab.
- Lienesch, J. NESDIS/Satellite Research Laboratory
- Long, C.S. NWS/Climate Prediction Center
- Miller, A.J. NWS/Climate Prediction Center
- Nagatani, R.M. NWS/Climate Prediction Center
- Oltmans, S. ERL/Climate Monitoring and Diagnostic Lab.
- Planet, W.G. NESDIS/Satellite Research Laboratory
- Solomon, S. ERL/Aeronomy Laboratory
- Stowe, L. NESDIS/Satellite Research Laboratory
Concerns of possible global ozone depletion (e.g., WMO/UNEP, 1992) have led to
major international programs to monitor and explain the observed ozone
variations in the stratosphere. In response to these, and other long-term
climate concerns, NOAA has established routine monitoring programs using both
ground-based and satellite measurement techniques (OFCM, 1988).
Selected indicators of stratospheric climate are presented in each Summary
from information contributed by NOAA personnel. A Summary for the Northern
Hemisphere is issued each April, and, for the Southern Hemisphere,
each December. These Summaries are available on the World-Wide-Web at the
site: http://www.cpc.ncep.noaa.gov
with location: products/stratosphere/winter_bulletins
Further information may be obtained from Alvin J. Miller
NOAA, Climate Prediction Center
5200 Auth Road
Camp Springs, MD 20746-4304
Telephone: (301) 763-8000 ext.7552
Fax: (301) 763-8125
E-mail: alvin.miller@noaa.gov
ABSTRACT:
Ozone measurements during the winter of 1994-1995 indicate that total column
ozone was unusually low over regions of the Northern Hemisphere. For middle
and high latitudes, ozone values were 10 to 20 percent lower than typical
values observed during these months in 1979 and the early 1980's. Over some
high latitude regions, such as Siberia, total ozone in 1994-95 had decreased
by up to 35 percent from 1979 values. Total ozone has decreased since 1979
over Northern Hemisphere mid- latitudes at the rate of about 4 percent per
decade. Little or no significant long-term trend is observed for the
equatorial region. Lower stratosphere daily minimum temperatures over the
north polar region in December 1994 and January 1995 reached record low
values. Temperatures observed were sufficiently low for chemical ozone
destruction on polar stratospheric clouds within the polar vortex to go during
the 1994-95 winter-spring period. A stratospheric warming during February 1995
interrupted the period of record low minimum temperatures, but record low
minimum temperatures returned in the polar region during March 1995.
I. DATA RESOURCES
The data available and appropriate references are listed below. This
combination of complementary data, from different platforms and sensors,
provides a strong capability to monitor global ozone, temperature and aerosols.
GROUND-BASED OBSERVATIONS |
Parameter |
Method |
Reference |
Total Ozone |
Dobson |
Komhyr et al., 1986 |
|
|
CMDL, 1990 |
Ozone Profiles |
Balloons |
Komhyr et al., 1989 |
|
|
CMDL, 1990 |
|
SATELLITE OBSERVATIONS |
Parameter |
Method |
Reference |
Total Ozone |
NOAA/SBUV/2 |
Planet et al., 1994 |
|
Nimbus-7 SBUV |
Mateer et al., 1971 |
Ozone Profiles |
|
Miller, 1989 |
|
|
Planet et al., 1994 |
|
|
Mateer et al., 1971 |
Temperature Profiles |
NOAA/TOVS |
Gelman et al., 1986 |
Aerosols |
NOAA/AVHRR |
Long & Stowe, 1993 |
|
We have used the total column ozone data from the NASA Nimbus -7 SBUV
instrument from 1979 through 1988, the NOAA-11 SBUV/2 from January 1989 to
August 1994. and the NOAA-9 SBUV/2 instrument beginning September 1994. The
orbital characteristics of the NOAA polar orbiting satellites are such that
the equatorial crossing times, over several years, are later in the day. For
the SBUV/2 instruments, the extremely high solar azimuth angles eventually
exceed the diffuser's calibrated range. This happened to the NOAA-11 SBUV/2 in
late 1994. Fortunately, the NOAA-9 instrument had migrated back into the
preferred solar azimuth angle range. After extensive comparisons with available
ground-based observations and with NOAA-11 (Crosby, personal communication), it
was determined that the NOAA-9 data are, on average, within two to four
percent of Dobson total ozone data. Consequently, we use the data from the
NOAA-9 SBUV/2 beginning in September 1994.
II. DISCUSSION
Figure 1 shows monthly average anomalies of zonal mean total column ozone, as
a function of latitude and time, from January 1979 to March 1995. Certain
aspects of long-term global ozone changes may be readily seen. In the
extra-tropics and polar regions, ozone is substantially lower in recent years
than in earlier years. The anomalies (percent difference) are derived relative
to each month's long-term average. No adjustments have been made to the data
from the three different satellite instruments, and it is very encouraging that
the transitions, between the NIMBUS-7 SBUV and the NOAA-11 data sets in
January 1989, and the NOAA-11 and the NOAA-9 data in September 1994, are very
smooth. Stolarski et al. (1992), and more recently Hollandsworth et al.
(1994) and Miller et al. (1994) have indicated that total ozone trends in the
mid-latitudes are statistically significant and are about -2 to -4 % per decade,
and that little or no significant trend exists over the equatorial region. Large
negative anomalies in the Northern Hemisphere extra-tropics during 1992- 1993
(Gleason et al., 1993) could be related to the Mt. Pinatubo eruption in
mid-1991. The anomalies decreased in 1994 along with the diminishing aerosol
loading. However, large negative anomalies again developed in 1994-95 over
the north polar region, with substantial negative ozone anomalies extending to
the northern extra-tropics. In the tropical region, a weak high anomaly is
seen in 1994-95, as part of the quasi-biennial oscillation of total ozone.
Geographical distributions of ozone and ozone changes are illustrated in the
next four figures. Monthly mean total ozone amounts for March 1995 are
shown in Figure 2. A region of high ozone (yellow and red colors) is located
over middle to high northern latitudes. Low values are shown over the north
polar region, and extending over Siberia to northern Greenland. These low total
ozone values (green and blue, 300 to 220 DU), are typical for tropical values,
in all months of the year, but are unusually low for the polar region.
Figure 3 shows the percent difference in monthly mean total ozone, between
March 1995 and March 1979. The 1979 base period is chosen because these
values are typical for the early data record. Decreases since 1979 in total
ozone of more than 40 percent, shown by the blue colors, extend over the north
polar region to northern Siberia. Decreases of greater than 20 percent (green)
cover a very large area of Siberia, northern Greenland and northern Canada.
Over most of the United States, March 1995 values were lower than those for
March 1979 by 15 to 20 percent. Small percent increases are shown over some
local areas of the tropics and mid-latitudes, but these increases are
short-term, regional effects, and are not representative of general, long-term
changes of ozone.
The region of low total ozone over northern Siberia and the north polar region
developed and grew during the months of January, February and March 1995.
Figures 3, 4 and 5 show that the large region of relatively low ozone over
Siberia (difference of the 1995 monthly mean from 1979 values) persisted for
several months, but the locations of other positive and negative ozone
differences from their 1979 values changed during the first three months of
1995. A region of persisting negative total ozone anomalies may be seen
around the international dateline, near Hawaii.
On two days in December 1994, total ozone measured at the NOAA/CMDL, Mauna Loa
observatory (MLO), Hawaii, dropped below 200 Dobson Units (DU), for the first
time since measurements began at this site (1963). Minimum annual total ozone
occurs at MLO at the end of December and the beginning of January in each year,
with some fluctuation in the minimum values from year to year.
In Figure 6, ozone anomalies (percent difference from the monthly averages for
the period 1964 to 1981) are shown for the 31 year record at MLO. The
anomalies show a long-term downward trend of about 1.2 percent per decade,
with an uncertainty of .38 percent for 95 percent confidence. The record low
winter ozone of 1994-95 at MLO, Hawaii was thus the result of an unusually large
INFORMATION MISSING
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