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Ground-based millimeter-wave observations of ozone in the upper stratosphere and mesosphere at Tsukuba and Nagoya
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Adv. Space Rex Vol. 26, No. 6, pp. 1017-1020,200O 0 2000 COSPAR. Published by Elsevier Science Ltd. All rights reserved Printed in Great Britain 0273-l 177100$20.00 + 0.00 PII: SO273-1177(00)00050-8
GROUND-BASED MILLIMETER-WAVE OZONE IN THE UPPER STRATOSPHERE TSUKUBA AND NAGOYA
OBSERVATIONS AND MESOSPHERE
OF AT
T. Nagahama’, H. Nakane’, M. Ninomiya’, H. Ogawa3, and Y. Fukui3
‘National Institute for Environmental Studies, Onogawa 16-2, Tsukuba, Ibaraki 30500.53, Japan ‘Global Environmental Forum, Inarimae 24-18, Tsukuba, Ibaraki 3050061, Japan 3Department of Astrophysics, Nagoya University, Nagoya 464-8602, Japan
ABSTRACT We report on ground-based observations of the upper stratospheric and mesospheric ozone by using two millimeterwave radiometers at the National Institute for Environmental Studies (NIES) in Tsukuba and Nagoya University since October 1995 and January 1992, respectively. The 613 to 60.6transition of ozone at 110.836 GHz was observed, and vertical profiles from 38 to 76 km were retrieved. Comparison with the radiometer and co-located ozone lidar results at 38 km shows reasonable agreement with each other, indicating that the radiometer data are reliable. From 19 months of observations, we have clearly detected seasonal and short-term variations of ozone at various altitudes. @2000 COSPAR. Published by Elsevier Science Ltd. INTRODUCTION Ground-based
millimeter-wave
radiometers are useful sensors for the monitoring of atmospheric minor constituents.
One of the important roles of the radiometers is to observe vertical profiles of ozone, especially in the upper stratosphae near 40 km where ozone depletion due to gas phase reactions is most effective. Since processes of ozone depletion in the upper stratosphere are simpler than those in the lower stratosphere where heterogeneous reactions are included in the polar and mid-latitude regions, depletion and expected gradual recovery of the ozone layer would be detected clearly in the upper stratosphere rather than in the lower stratosphere. Therefore, the millimeter-wave observations are expected to confirm such recovery of the ozone layer and to assess our understandings of ozone conditions in future. For this purpose, the National Institute for Environmental Studies (NIES) and Nagoya University developed two millimeter-wave radiometers, and have been measuring the upper stratospheric and mesospheric ozone in Tsukuba (36”N. 14O”E) and Nagoya (35’N, 137”E) since October 1995 and January 1992, respectively. In this paper, we describe the radiometer systems and data analysis. The seasonal and short-term variations of ozone that wedetected as well as the comparison with lidar data are also presented. HARDWARE DESCRIPTION The instrument consists of an antenna, a superconductor-insulator-superconductor (SIS) mixer receiver and an acousto-optical spectrometer (AOS). The block diagram of the instrument is shown in Figure 1. The ozone emission is collected by the offset parabolic reflector whose diameter is 10 cm, and is detected by the SIS mixer receiver cooled at 4 K by a closed-cycle refrigerator. A receiver noise temperature is -50 K in single side band. The AOS covers a 60 MHz bandwidth with 2048 channels, and an effective frequency resolution for each channel is 40 kHz. The whole system is controlled by a PC-based microcomputer. Spectral line intensities were calibrated by using two thermal emissions from a hot reference at 300 K and the sky. We observed the 61s to 60,atransition of ozone at 110.836 GHz. The ozone spectra were obtained every 5 minutes by using the frequency switching technique. The central observing frequencies differing by 30 MHz are switched every 2 seconds, and one measurement is subtracted to the other. The effective bandwidth in spectrum is, therefore, 30 MHz. 1017
T. Nagahama et al.
1018
Hot Reference Yy
300K
Lo. osc.
Fig. 1. Block diagram of the millimeter-wave radiometer at 110 GHz.
ANALYSIS Vertical profiles of ozone mixing ratio were retrieved from the spectra by using the optimal estimation algorithm formulated by Rodgers (1976). In this algorithm, we fixed the covariance of the observed brightness temperature to avoid variation in vertical resolution according to the rms noise level of the observed spectrum. For constructing a forward model, we computed the weighting functions by adopting temperature and pressure models which were obtained from the CIRA1986 climatology (Rees et al. 1990) by the spline interpolation every 1 km at 36”N. We note that difference between adopted and true temperature profiles does not affect seriously the error in retrieval because the ozone emission at 110 GHz is not sensitive to temperature. From numerical analysis, we estimated the error in retrieval to be within 5%. The absorption coefficient was calculated by using molecular line parameters taken from the HITRAN database (Data are archived in CD-ROM by Rothman 1996). For data analysis, we used a finite differentiation of the brightness temperature at two different frequencies because we cannot know the absolute brightness temperature of the spectra obtained with the frequency switching. The vertical profiles of ozone from 38 to 76 km, at every 2 km in altitude, were currently retrieved. Using the averaging kernel, the vertical resolution of the measurement was estimated to be 14 km. The ozone spectra integrated over 1 hour and the retrieved vertical profiles obtained on January 26,1998 are shown in Figure 2. The enhancement of the mesospheric ozone during the nighttime, especially above 56 km, is clearly seen. 10
January 26, 1998
Januafy 26,1998 . . . . . . . . . . . . . . . . . . -dY(12:00,3FX) nl#lyoQo., do)
.I0
-10
4
df(ML,
5
10
15
0
1
2
3
4
6
Oi!ONE Mixing Ratlo
6
7
8
9
10
(ppmv)
Fig. 2. (left) Observed ozone spectra and their residuals of fitting by the forward model calculation in the daytime and nighttime on January 26, 1998. (right) Retrieved vertical profiles of ozone mixing ratio.
Ground-Based mm-Wave Observations of Ozone
1019
RESULTS AND DISCUSSION Figure 3 shows convolved ozone number densities at 38 km measured with the millimeter-wave radiometer and colocated ozone lidar in Tsukuba, which were calculated with each other’s vertical resolution to make the comparison with the same resolution. The detail of the ozone lidar in NIES was described by Nakane et al. (1993). The radiometer data was an average over 6 hours of the nighttime. The ozone variations with the radiometer is similar to that with the Mar, but the convolved ozone number density with the radiometer is on average -8% lower than that with the lidar. From error analysis, we found that our radiometer data has a systematic error in calibration which is due to uncertainties of effective sky temperature and tropospheric opacity. We estimated this error to be about 6-7% in negative, and therefore, difference between the radiometer and Mar data can be understood as the error in calibration. Removing the error, the radiometer measurements are consistent with those with the Mar within a few percent, Thus, we conclude that the present radiometer measurements in Tsukuba are reliable and appropriate for the long-term monitoring of ozone. 38km 1.310’”
1.2 10” +-
l
MMdayiime
d MMnighttime
E .*
1.1 to”
! 1
1.010”
5 uJ
8.010”
6 :
6.0 10”
7.0 IO” JsnR 1197
AprR2B7
JulR287
cHRom7
Jan/l Qls6
Date
Fig. 3. Convolved ozone number densities for the radiometer and lidar in Tsukuba at 38 km.
comparison and correlation with ozone mixing ratios at 38 km in Tsukuba and Nagoya are shown in Figure 4. All the data were 6 hour averages in the nighttime. From 5 weeks of observations, the ozone data at the two stations show similar variations in a few weeks, indicating that such a variation may be natural. A problem is that the value in Nagoya is on average -12% lower than those in Tsukuba. Since the data in Tsukuba is consistent with that of the ozone lidar as shown above, this discrepancy may be caused by some errors of the Nagoya instrument, mainly error in calibration. Next,
38 km (Night) 9.0
6.0
,YL”“~“”
38 km (Night) I
I
I
1 R=0.93
Few11
FebRl
6.0 ’ 7.0
I
,
I
7.5
6.0
6.5
Mixing Ratio in Tsukuba
0.0
(ppmv)
Fig. 4. (left) Ozone mixing ratios at 38 km in Tsukuba and Nagoya from January 10 to February 28,1998, and (right) correlation between them. The data are averaged in 6 hours of the nighttime. In the right figure, a line denotes the best fit with the correlation coefficient of 0.93.
1020
T. Nagahama et al.
Figure 5 shows the time variations of ozone mixing ratio at 50 and 76 km in Tsukuba since October 1996. The day and night data were integrated over 6 hours of the daytime and nighttime, respectively. We found seasonal and short-term variations in ozone mixing ratio. At 50 km, the annual variation of the ozone mixing ratio has a minimum in summer and a maximum in winter which is significant, being generally consistent with a climatological model (Keating et al. 1990). The remarkable feature at 50 km is a sudden increasing of ozone which occurred in November 1997, when the ozone mixing ratio had increased about 25% in a few weeks. At 76 km, there is an apparent semi-annual variation of ozone mixing ratio, being well fitted by a sine curve with a half year period. This feature is different from that in the SME data (Thomas 1990) which shows that the spring peak of ozone mixing ratio is about 1.7 times larger than the autumn one. Theoretical studies indicate that the semi-annual variation of ozone in the upper mesosphere is induced by the variation of vertical eddy diffusion due to breaking gravity waves (Garcia & Solomon 1985). Murayama et al. (1994) found, from the MU radar observations, a semi-annual variation of the gravity wave energy at 65-85 km that has equinoctial minima which are almost the same. Considering the gravity wave activity and the theoretical models, the ozone mixing ratio in the upper mesosphere is expected to be the same in equinox. The present result is similar to this expected situation, and therefore, we believe that the semi-annual variation at 76 km we detected is real. 50km
ocvl
ma
FoW15,97
Jmll5B7 Date
76 km
OcVl s/97
Feb/l&QI
ocm7rQa
FebIl5R7
JuvlWA7
Fob/UrPO
Date
Fig. 5. Ozone mixing ratios in Tsukuba at 50 km (left) and 76 km (right). Filled circles and open triangles are the values averaged in 6 hours of the daytime and nighttime, respectively.
ACKNOWLEDGMENTS The authors thank to Minoru Suzuki and Atsushi Morihira of Fujitsu VLSI Ltd. for maintaining the instruments. REFERENCES Garcia, R. R., and S. Solomon, The effect of breaking gravity waves on the dynamics and chemical composition of the mesosphere and lower thermosphere, J. Geophys. Res., !M,3850 (1985). Keating, G. M., M. C. Pins, and D. F. Young, Ozone reference models for the middle atmosphere, Adv. Space Res., 10, No. 12,317 (1990). Murayama, Y., T. Tsuda, and S. Fukao, Seasonal variation of gravity wave activity in the lower atmosphere observed with the MU radar, J. Geophys. Res., 99,23,057 (1994). Nakane, H., S. Hayashida, N. Sugimoto, I. Matsui, and Y. Sasano, Ozone lidar monitoring, in Annuul Report OR Global Environmental Monitoring (1993), pp. l-3 1, Center for Global Environmental Research, National Institute for Environmental Studies, Tsukuba, Japan (1993). Rees, D., J. J. Barnett, and K. Labitzke, COSPAR International Reference Atmosphere: 1986, Part II: Middle Atmos phere Models, Adv. Space Res., 12, No 12 (1990). Rodgers, C. D., Retrieval of atmospheric temperature and composition from remote measurements of thermal radiation, Rev. Geophys., 14,609 (1976). Rothman, L. S., The HITRAN database, archived in CD-ROM (1996). Thomas, R. J., Seasonal ozone variations in the upper mesosphere, J. Geophys. Res., 95,7395 (1990).
Adv. Space Rex Vol. 26, No. 6, pp. 1017-1020,200O 0 2000 COSPAR. Published by Elsevier Science Ltd. All rights reserved Printed in Great Britain 0273-l 177100$20.00 + 0.00 PII: SO273-1177(00)00050-8
GROUND-BASED MILLIMETER-WAVE OZONE IN THE UPPER STRATOSPHERE TSUKUBA AND NAGOYA
OBSERVATIONS AND MESOSPHERE
OF AT
T. Nagahama’, H. Nakane’, M. Ninomiya’, H. Ogawa3, and Y. Fukui3
‘National Institute for Environmental Studies, Onogawa 16-2, Tsukuba, Ibaraki 30500.53, Japan ‘Global Environmental Forum, Inarimae 24-18, Tsukuba, Ibaraki 3050061, Japan 3Department of Astrophysics, Nagoya University, Nagoya 464-8602, Japan
ABSTRACT We report on ground-based observations of the upper stratospheric and mesospheric ozone by using two millimeterwave radiometers at the National Institute for Environmental Studies (NIES) in Tsukuba and Nagoya University since October 1995 and January 1992, respectively. The 613 to 60.6transition of ozone at 110.836 GHz was observed, and vertical profiles from 38 to 76 km were retrieved. Comparison with the radiometer and co-located ozone lidar results at 38 km shows reasonable agreement with each other, indicating that the radiometer data are reliable. From 19 months of observations, we have clearly detected seasonal and short-term variations of ozone at various altitudes. @2000 COSPAR. Published by Elsevier Science Ltd. INTRODUCTION Ground-based
millimeter-wave
radiometers are useful sensors for the monitoring of atmospheric minor constituents.
One of the important roles of the radiometers is to observe vertical profiles of ozone, especially in the upper stratosphae near 40 km where ozone depletion due to gas phase reactions is most effective. Since processes of ozone depletion in the upper stratosphere are simpler than those in the lower stratosphere where heterogeneous reactions are included in the polar and mid-latitude regions, depletion and expected gradual recovery of the ozone layer would be detected clearly in the upper stratosphere rather than in the lower stratosphere. Therefore, the millimeter-wave observations are expected to confirm such recovery of the ozone layer and to assess our understandings of ozone conditions in future. For this purpose, the National Institute for Environmental Studies (NIES) and Nagoya University developed two millimeter-wave radiometers, and have been measuring the upper stratospheric and mesospheric ozone in Tsukuba (36”N. 14O”E) and Nagoya (35’N, 137”E) since October 1995 and January 1992, respectively. In this paper, we describe the radiometer systems and data analysis. The seasonal and short-term variations of ozone that wedetected as well as the comparison with lidar data are also presented. HARDWARE DESCRIPTION The instrument consists of an antenna, a superconductor-insulator-superconductor (SIS) mixer receiver and an acousto-optical spectrometer (AOS). The block diagram of the instrument is shown in Figure 1. The ozone emission is collected by the offset parabolic reflector whose diameter is 10 cm, and is detected by the SIS mixer receiver cooled at 4 K by a closed-cycle refrigerator. A receiver noise temperature is -50 K in single side band. The AOS covers a 60 MHz bandwidth with 2048 channels, and an effective frequency resolution for each channel is 40 kHz. The whole system is controlled by a PC-based microcomputer. Spectral line intensities were calibrated by using two thermal emissions from a hot reference at 300 K and the sky. We observed the 61s to 60,atransition of ozone at 110.836 GHz. The ozone spectra were obtained every 5 minutes by using the frequency switching technique. The central observing frequencies differing by 30 MHz are switched every 2 seconds, and one measurement is subtracted to the other. The effective bandwidth in spectrum is, therefore, 30 MHz. 1017
T. Nagahama et al.
1018
Hot Reference Yy
300K
Lo. osc.
Fig. 1. Block diagram of the millimeter-wave radiometer at 110 GHz.
ANALYSIS Vertical profiles of ozone mixing ratio were retrieved from the spectra by using the optimal estimation algorithm formulated by Rodgers (1976). In this algorithm, we fixed the covariance of the observed brightness temperature to avoid variation in vertical resolution according to the rms noise level of the observed spectrum. For constructing a forward model, we computed the weighting functions by adopting temperature and pressure models which were obtained from the CIRA1986 climatology (Rees et al. 1990) by the spline interpolation every 1 km at 36”N. We note that difference between adopted and true temperature profiles does not affect seriously the error in retrieval because the ozone emission at 110 GHz is not sensitive to temperature. From numerical analysis, we estimated the error in retrieval to be within 5%. The absorption coefficient was calculated by using molecular line parameters taken from the HITRAN database (Data are archived in CD-ROM by Rothman 1996). For data analysis, we used a finite differentiation of the brightness temperature at two different frequencies because we cannot know the absolute brightness temperature of the spectra obtained with the frequency switching. The vertical profiles of ozone from 38 to 76 km, at every 2 km in altitude, were currently retrieved. Using the averaging kernel, the vertical resolution of the measurement was estimated to be 14 km. The ozone spectra integrated over 1 hour and the retrieved vertical profiles obtained on January 26,1998 are shown in Figure 2. The enhancement of the mesospheric ozone during the nighttime, especially above 56 km, is clearly seen. 10
January 26, 1998
Januafy 26,1998 . . . . . . . . . . . . . . . . . . -dY(12:00,3FX) nl#lyoQo., do)
.I0
-10
4
df(ML,
5
10
15
0
1
2
3
4
6
Oi!ONE Mixing Ratlo
6
7
8
9
10
(ppmv)
Fig. 2. (left) Observed ozone spectra and their residuals of fitting by the forward model calculation in the daytime and nighttime on January 26, 1998. (right) Retrieved vertical profiles of ozone mixing ratio.
Ground-Based mm-Wave Observations of Ozone
1019
RESULTS AND DISCUSSION Figure 3 shows convolved ozone number densities at 38 km measured with the millimeter-wave radiometer and colocated ozone lidar in Tsukuba, which were calculated with each other’s vertical resolution to make the comparison with the same resolution. The detail of the ozone lidar in NIES was described by Nakane et al. (1993). The radiometer data was an average over 6 hours of the nighttime. The ozone variations with the radiometer is similar to that with the Mar, but the convolved ozone number density with the radiometer is on average -8% lower than that with the lidar. From error analysis, we found that our radiometer data has a systematic error in calibration which is due to uncertainties of effective sky temperature and tropospheric opacity. We estimated this error to be about 6-7% in negative, and therefore, difference between the radiometer and Mar data can be understood as the error in calibration. Removing the error, the radiometer measurements are consistent with those with the Mar within a few percent, Thus, we conclude that the present radiometer measurements in Tsukuba are reliable and appropriate for the long-term monitoring of ozone. 38km 1.310’”
1.2 10” +-
l
MMdayiime
d MMnighttime
E .*
1.1 to”
! 1
1.010”
5 uJ
8.010”
6 :
6.0 10”
7.0 IO” JsnR 1197
AprR2B7
JulR287
cHRom7
Jan/l Qls6
Date
Fig. 3. Convolved ozone number densities for the radiometer and lidar in Tsukuba at 38 km.
comparison and correlation with ozone mixing ratios at 38 km in Tsukuba and Nagoya are shown in Figure 4. All the data were 6 hour averages in the nighttime. From 5 weeks of observations, the ozone data at the two stations show similar variations in a few weeks, indicating that such a variation may be natural. A problem is that the value in Nagoya is on average -12% lower than those in Tsukuba. Since the data in Tsukuba is consistent with that of the ozone lidar as shown above, this discrepancy may be caused by some errors of the Nagoya instrument, mainly error in calibration. Next,
38 km (Night) 9.0
6.0
,YL”“~“”
38 km (Night) I
I
I
1 R=0.93
Few11
FebRl
6.0 ’ 7.0
I
,
I
7.5
6.0
6.5
Mixing Ratio in Tsukuba
0.0
(ppmv)
Fig. 4. (left) Ozone mixing ratios at 38 km in Tsukuba and Nagoya from January 10 to February 28,1998, and (right) correlation between them. The data are averaged in 6 hours of the nighttime. In the right figure, a line denotes the best fit with the correlation coefficient of 0.93.
1020
T. Nagahama et al.
Figure 5 shows the time variations of ozone mixing ratio at 50 and 76 km in Tsukuba since October 1996. The day and night data were integrated over 6 hours of the daytime and nighttime, respectively. We found seasonal and short-term variations in ozone mixing ratio. At 50 km, the annual variation of the ozone mixing ratio has a minimum in summer and a maximum in winter which is significant, being generally consistent with a climatological model (Keating et al. 1990). The remarkable feature at 50 km is a sudden increasing of ozone which occurred in November 1997, when the ozone mixing ratio had increased about 25% in a few weeks. At 76 km, there is an apparent semi-annual variation of ozone mixing ratio, being well fitted by a sine curve with a half year period. This feature is different from that in the SME data (Thomas 1990) which shows that the spring peak of ozone mixing ratio is about 1.7 times larger than the autumn one. Theoretical studies indicate that the semi-annual variation of ozone in the upper mesosphere is induced by the variation of vertical eddy diffusion due to breaking gravity waves (Garcia & Solomon 1985). Murayama et al. (1994) found, from the MU radar observations, a semi-annual variation of the gravity wave energy at 65-85 km that has equinoctial minima which are almost the same. Considering the gravity wave activity and the theoretical models, the ozone mixing ratio in the upper mesosphere is expected to be the same in equinox. The present result is similar to this expected situation, and therefore, we believe that the semi-annual variation at 76 km we detected is real. 50km
ocvl
ma
FoW15,97
Jmll5B7 Date
76 km
OcVl s/97
Feb/l&QI
ocm7rQa
FebIl5R7
JuvlWA7
Fob/UrPO
Date
Fig. 5. Ozone mixing ratios in Tsukuba at 50 km (left) and 76 km (right). Filled circles and open triangles are the values averaged in 6 hours of the daytime and nighttime, respectively.
ACKNOWLEDGMENTS The authors thank to Minoru Suzuki and Atsushi Morihira of Fujitsu VLSI Ltd. for maintaining the instruments. REFERENCES Garcia, R. R., and S. Solomon, The effect of breaking gravity waves on the dynamics and chemical composition of the mesosphere and lower thermosphere, J. Geophys. Res., !M,3850 (1985). Keating, G. M., M. C. Pins, and D. F. Young, Ozone reference models for the middle atmosphere, Adv. Space Res., 10, No. 12,317 (1990). Murayama, Y., T. Tsuda, and S. Fukao, Seasonal variation of gravity wave activity in the lower atmosphere observed with the MU radar, J. Geophys. Res., 99,23,057 (1994). Nakane, H., S. Hayashida, N. Sugimoto, I. Matsui, and Y. Sasano, Ozone lidar monitoring, in Annuul Report OR Global Environmental Monitoring (1993), pp. l-3 1, Center for Global Environmental Research, National Institute for Environmental Studies, Tsukuba, Japan (1993). Rees, D., J. J. Barnett, and K. Labitzke, COSPAR International Reference Atmosphere: 1986, Part II: Middle Atmos phere Models, Adv. Space Res., 12, No 12 (1990). Rodgers, C. D., Retrieval of atmospheric temperature and composition from remote measurements of thermal radiation, Rev. Geophys., 14,609 (1976). Rothman, L. S., The HITRAN database, archived in CD-ROM (1996). Thomas, R. J., Seasonal ozone variations in the upper mesosphere, J. Geophys. Res., 95,7395 (1990).