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Monitoring the stratosphere with satellites and the network for detection of stratospheric change
Palaeogeography, Palaeoclimatology, Palaeoecologv (Global and Planetary Change Section), 90 (1991) 69 71
69
Elsevier Science Publishers B.V., Amsterdam
Condensed Paper
Monitoring the stratosphere with satellites and the network for detection of stratospheric change A l v i n J. Miller NOAA / N W S / NMC / Climate Analysis Center, WWB, Room 811, Washington, DC 20233, USA
ABSTRACT Miller, A.J., 1991. Monitoring the stratosphere with satellites and the network for detection of stratospheric change. Palaeogeogr., Palaeoclimatol., Palaeoecol (Global Planet Change Sect.), 90: 69-71. The emphasis in the series of papers in this issue is the use of operational satellite information. Within this paper, however, we will examine a slightly different aspect of the problem. We will discuss how the satellite and ground-based observations, from the viewpoint of monitoring the stratosphere are synergistic in that each provides a key part of the total information necessary. Finally, we will look toward the future of the ground-based data program and present information on the ground-based data program and present information on the Network for Detection of Stratospheric Change.
Introduction From the perspective of monitoring the stratosphere for evidence of changes in ozone and temperature, certain fundamental issues arise when considering the role of satellite and ground-based data: (1) The N O A A operational satellite series of measurements is designed to provide near-global coverage such that trend estimates are not influenced by regional coverage only. (2) History has shown that in the harsh environment of space, it is very difficult to maintain a long-term calibration of the satellite instruments; hence ground-based observations have been critical in defining changes of calibration with time or instrument-to-instrument differences. (3) The ground-based observations, while limited in number, have a data record well beyond the initiation of the operational satellite program, from the mid-60's compared to the late 70's. This results in information over an additional solar
cycle which can be critical in assessing true causal association. (4) Finally, the satellite data have gaps in their vertical coverage and we must rely on the groundbased data to fill in these missing areas. Item (1) is, of course, a basic tenet of the satellite program and will be discussed further in the discussion of item (3) and the statistics of trend analysis. Item (2) has been presented in detail elsewhere in this issue; Planet et al. (1991) for ozone and Gelman et al. (1991) for temperature profiles. Consequently, we will concentrate below on the remaining issues of coverage and gaps.
Statistical analysis If we assume a very simplified form of linear trend with time, t, in a parameter, y, statistically we might express this in the form: Y= [y] +
b(t-[t])
(1)
70
A.J. MILLER
where the square brackets represent the average values over the record. For this formulation the variance of the coefficient, b, is given by: k
Var.{b) = 0 2 / Z (t- [,])2
(2)
30
' ' ' ' I ' T T ~ T I ' ' '
_,,,,l,,,,l~r-,,
25 20
lo
X
t--1 K
where k is the number of observation and o 2 is approximated by: Z
o
~LUI,,
, ,I,,
-I0
k
$2:
5
(Y,-
Y,)2/( k - 2)
(3)
i--1
We see, then, that the confidence level we may ascribe to our determination of the trend coefficient, b, is defined by several factors; the variance of the data about the linear trend and the length of record. In the context of the discussion, here, the satellite systems provide near-global coverage and tend to limit the random sampling component. The ground-based observations, on the other hand, have the longer record which tends to compensate for their inherently greater sampling variability. In a similar fashion, with the longer record, when we expand this simple trend model to include terms for solar cycle and quasi-biennial components of variability the longer record helps to make them more deterministic. Overall, then, each system should be considered as an equal component of the trend analysis system. Vertical coverage
The operational S B U V / 2 ozone satellite measurement program is designed to determine total ozone and ozone vertical profiles in the range from 25-55 km (OFCM, 1989). More recently, Tiao and co-workers (WMO, 1989) have examined the ground-based balloon ozonesonde data for 9 stations from the mid-60's through 1986 and their results are plotted in Fig. 1. We see that in the lower troposphere a positive trend results from the data, but the noise level is so great that the results are not statistically different from zero. In the upper troposphere and lower stratosphere, however. a negative trend exists that is statistically
-15
t A L , t L L J L , [ ~ ,", , I
0
-5
, ,,,:
~0
5
20
15
~/DECADE
Fig. 1. Balloon ozonesonde trend estimates from the mid-1960's through 1986 (Tiao et al. in WMO 1989).
significant and appears to account for the major portion of the total ozone trend (WMO, 1989). It is important to recognize from the above discussion that the trend in the lower stratosphere and upper troposphere is not within the measurement region of the S B U V / 2 . At best, from the values of total ozone and the profiles above 25 km an inference can be made about the region below 25 km. One aspect not yet mentioned is the availability of ozone information from the TOVS operational satellite as described by Coriolle (this issue) and Neuendorffer (this issue) in this issue. As the estimates of total ozone from TOVS essentially represent the values in the upper troposphere and lower stratosphere it may well be that a combination of information from the two satellite systems will provide the necessary information, but this has to be explored. With respect to temperature profile information, the important issue is that the launch of the last Stratospheric Sounding Unit is planned for about 1992. After this the operational temperature profiles will come from the Advanced Microwave Sounding Unit which extends observations up to about 40 km. As indicated in the statement of requirements for stratospheric monitoring (OFCM, 1989) profile information up to at least 50 km is required. Currently, several observational methods have been suggested that may extend the measurements to the upper stratosphere, but these may not be operational before the mid-1990's, if then. This could result in a significant gap in the record.
M O N I T O R I N G 1tt1£ S T R A T O S P H E R E W I T t t S A T E L L I T E S
Ground-based systems Planet et al. (this issue) and Gelman (this issue) have discussed some of the aspects of current ground-based data: their strengths and weaknesses. In this section we will look to the future and, in particular, the next-generation Network for Detection of Stratospheric Change. As part of its Climate and Global Change Program, NOAA is participating in the global Network for Detection of Stratospheric Change. This is a multi-agency and internationally supported program whose goal is, in conjunction with the NOAA operational satellite program, to provide the earliest possible detection of changes in the stratosphere and the means to understand them. Toward this, the following ground-based measurements are considered the highest priority: (1) Column ozone FTIR, UV/VIS, Microwave (2) Vertical ozone profile - Lidar, Microwave (3) Vertical temperature profile Lidar (4) Vertical profile of C10 - Microwave (5) Vertical profile of H20 - Microwave (6) Vertical distribution of aerosols - Lidar (7) Vertical profile or column NO 2 - UV,/VIS, FTI R
(8) Stratospheric column of HC1 FTIR (9) Vertical profiles of C H 4 and N20 - FTIR, Microwave (10) Other species (HNO 3, NOB, CIONO2) FTIR, U V / V I S
71
Currently, two sites have been selected for primary consideration; The Observatoire Haute Provence in France and the N O A A / G e o p h y s i c a l Monitoring for Climate Change site at Mauna Loa Observatory. Several additional sites are under consideration with a possible 6 station global network the likely disposition over the next several years.
Summary In summary, we see that with respect to the stratospheric monitoring program the overall combination of the operational satellite program and a well-calibrated ground-based measurement program is truly synergistic. Each provides a critical component of the necessary measurement. We stress, however, that the critical element of the entire program is high quality and calibration which requires, in turn, a high level of program planning and coordination.
References OFCM (Office of the Federal Coordinator for Meteorological Services and Supporting Research), 1989. National Plan for Stratospheric Monitoring, 1988-1997. FCM-P17-1989, 124 pp. WMO (World Meteorological Organization), 1989. Scientific Assessment of Stratospheric Ozone, 1989, Vol. 1. WMO Rep. No. 20, 486 pp.
69
Elsevier Science Publishers B.V., Amsterdam
Condensed Paper
Monitoring the stratosphere with satellites and the network for detection of stratospheric change A l v i n J. Miller NOAA / N W S / NMC / Climate Analysis Center, WWB, Room 811, Washington, DC 20233, USA
ABSTRACT Miller, A.J., 1991. Monitoring the stratosphere with satellites and the network for detection of stratospheric change. Palaeogeogr., Palaeoclimatol., Palaeoecol (Global Planet Change Sect.), 90: 69-71. The emphasis in the series of papers in this issue is the use of operational satellite information. Within this paper, however, we will examine a slightly different aspect of the problem. We will discuss how the satellite and ground-based observations, from the viewpoint of monitoring the stratosphere are synergistic in that each provides a key part of the total information necessary. Finally, we will look toward the future of the ground-based data program and present information on the ground-based data program and present information on the Network for Detection of Stratospheric Change.
Introduction From the perspective of monitoring the stratosphere for evidence of changes in ozone and temperature, certain fundamental issues arise when considering the role of satellite and ground-based data: (1) The N O A A operational satellite series of measurements is designed to provide near-global coverage such that trend estimates are not influenced by regional coverage only. (2) History has shown that in the harsh environment of space, it is very difficult to maintain a long-term calibration of the satellite instruments; hence ground-based observations have been critical in defining changes of calibration with time or instrument-to-instrument differences. (3) The ground-based observations, while limited in number, have a data record well beyond the initiation of the operational satellite program, from the mid-60's compared to the late 70's. This results in information over an additional solar
cycle which can be critical in assessing true causal association. (4) Finally, the satellite data have gaps in their vertical coverage and we must rely on the groundbased data to fill in these missing areas. Item (1) is, of course, a basic tenet of the satellite program and will be discussed further in the discussion of item (3) and the statistics of trend analysis. Item (2) has been presented in detail elsewhere in this issue; Planet et al. (1991) for ozone and Gelman et al. (1991) for temperature profiles. Consequently, we will concentrate below on the remaining issues of coverage and gaps.
Statistical analysis If we assume a very simplified form of linear trend with time, t, in a parameter, y, statistically we might express this in the form: Y= [y] +
b(t-[t])
(1)
70
A.J. MILLER
where the square brackets represent the average values over the record. For this formulation the variance of the coefficient, b, is given by: k
Var.{b) = 0 2 / Z (t- [,])2
(2)
30
' ' ' ' I ' T T ~ T I ' ' '
_,,,,l,,,,l~r-,,
25 20
lo
X
t--1 K
where k is the number of observation and o 2 is approximated by: Z
o
~LUI,,
, ,I,,
-I0
k
$2:
5
(Y,-
Y,)2/( k - 2)
(3)
i--1
We see, then, that the confidence level we may ascribe to our determination of the trend coefficient, b, is defined by several factors; the variance of the data about the linear trend and the length of record. In the context of the discussion, here, the satellite systems provide near-global coverage and tend to limit the random sampling component. The ground-based observations, on the other hand, have the longer record which tends to compensate for their inherently greater sampling variability. In a similar fashion, with the longer record, when we expand this simple trend model to include terms for solar cycle and quasi-biennial components of variability the longer record helps to make them more deterministic. Overall, then, each system should be considered as an equal component of the trend analysis system. Vertical coverage
The operational S B U V / 2 ozone satellite measurement program is designed to determine total ozone and ozone vertical profiles in the range from 25-55 km (OFCM, 1989). More recently, Tiao and co-workers (WMO, 1989) have examined the ground-based balloon ozonesonde data for 9 stations from the mid-60's through 1986 and their results are plotted in Fig. 1. We see that in the lower troposphere a positive trend results from the data, but the noise level is so great that the results are not statistically different from zero. In the upper troposphere and lower stratosphere, however. a negative trend exists that is statistically
-15
t A L , t L L J L , [ ~ ,", , I
0
-5
, ,,,:
~0
5
20
15
~/DECADE
Fig. 1. Balloon ozonesonde trend estimates from the mid-1960's through 1986 (Tiao et al. in WMO 1989).
significant and appears to account for the major portion of the total ozone trend (WMO, 1989). It is important to recognize from the above discussion that the trend in the lower stratosphere and upper troposphere is not within the measurement region of the S B U V / 2 . At best, from the values of total ozone and the profiles above 25 km an inference can be made about the region below 25 km. One aspect not yet mentioned is the availability of ozone information from the TOVS operational satellite as described by Coriolle (this issue) and Neuendorffer (this issue) in this issue. As the estimates of total ozone from TOVS essentially represent the values in the upper troposphere and lower stratosphere it may well be that a combination of information from the two satellite systems will provide the necessary information, but this has to be explored. With respect to temperature profile information, the important issue is that the launch of the last Stratospheric Sounding Unit is planned for about 1992. After this the operational temperature profiles will come from the Advanced Microwave Sounding Unit which extends observations up to about 40 km. As indicated in the statement of requirements for stratospheric monitoring (OFCM, 1989) profile information up to at least 50 km is required. Currently, several observational methods have been suggested that may extend the measurements to the upper stratosphere, but these may not be operational before the mid-1990's, if then. This could result in a significant gap in the record.
M O N I T O R I N G 1tt1£ S T R A T O S P H E R E W I T t t S A T E L L I T E S
Ground-based systems Planet et al. (this issue) and Gelman (this issue) have discussed some of the aspects of current ground-based data: their strengths and weaknesses. In this section we will look to the future and, in particular, the next-generation Network for Detection of Stratospheric Change. As part of its Climate and Global Change Program, NOAA is participating in the global Network for Detection of Stratospheric Change. This is a multi-agency and internationally supported program whose goal is, in conjunction with the NOAA operational satellite program, to provide the earliest possible detection of changes in the stratosphere and the means to understand them. Toward this, the following ground-based measurements are considered the highest priority: (1) Column ozone FTIR, UV/VIS, Microwave (2) Vertical ozone profile - Lidar, Microwave (3) Vertical temperature profile Lidar (4) Vertical profile of C10 - Microwave (5) Vertical profile of H20 - Microwave (6) Vertical distribution of aerosols - Lidar (7) Vertical profile or column NO 2 - UV,/VIS, FTI R
(8) Stratospheric column of HC1 FTIR (9) Vertical profiles of C H 4 and N20 - FTIR, Microwave (10) Other species (HNO 3, NOB, CIONO2) FTIR, U V / V I S
71
Currently, two sites have been selected for primary consideration; The Observatoire Haute Provence in France and the N O A A / G e o p h y s i c a l Monitoring for Climate Change site at Mauna Loa Observatory. Several additional sites are under consideration with a possible 6 station global network the likely disposition over the next several years.
Summary In summary, we see that with respect to the stratospheric monitoring program the overall combination of the operational satellite program and a well-calibrated ground-based measurement program is truly synergistic. Each provides a critical component of the necessary measurement. We stress, however, that the critical element of the entire program is high quality and calibration which requires, in turn, a high level of program planning and coordination.
References OFCM (Office of the Federal Coordinator for Meteorological Services and Supporting Research), 1989. National Plan for Stratospheric Monitoring, 1988-1997. FCM-P17-1989, 124 pp. WMO (World Meteorological Organization), 1989. Scientific Assessment of Stratospheric Ozone, 1989, Vol. 1. WMO Rep. No. 20, 486 pp.