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Stratospheric Processes And their Role in Climate
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Stratospheric Processes And their Role in Climate
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| Home | Initiatives | Organisation | Publications | Meetings | Acronyms and Abbreviations | Useful Links |
Report on the International Symposium on "Stratospheric Variations and Climate"
Fukuoka, Japan, November 12 –15, 2002Saburo Miyahara, Kyushu Univ., Fukuoka, Japan
Toshihiko Hirooka, Kyushu Univ., Fukuoka, Japan
Masato Shiotani, RASC, Kyoto Univ., Uji, Japan
Masaaki Takahashi, CCSR, Univ. of Tokyo, Tokyo, Japan
Shigeo Yoden, Kyoto Univ., Kyoto, Japan (yoden@kugi.kyoto-u.ac.jp)
Group photography on November 13, 2002 during the International Symposium on "Stratospheric Variations and Climate" Introduction
Middle atmosphere sciences have rapidly progressed in the last several decades, owing to the development of observational methods, computer facilities, and theories of middle atmosphere dynamics. On the other hand, investigations of global stratospheric climate-change, such as ozone depletion in the polar regions and cooling of the stratosphere, have drawn growing social attention.
Recognising the importance of stratospheric processes for the climate system, the WCRP set up a research project SPARC. Working in closer cooperation with this international project, we have been carrying out a four-year project from 1999 to 2002 “Variations of Dynamical Processes and Ozone in the Stratosphere and Their Role in Climate” under the Grant-in-Aid for Scientific Research on Priority Areas of the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan.
This symposium had been planed to discuss important issues related to stratospheric variations and climate under the attendance of international researchers. It was sponsored jointly by MEXT and Faculty of Science, Kyushu University. It consisted of three sessions and two special sessions:
(1) Variability of the Troposphere-Stratosphere (T-S) Coupled System
(2) Upper Troposphere/Lower Stratosphere (UT/LS) and Tropical Tropopause Layer (TTL)
(3) Chemistry-Climate Interaction
(S1) Special Talks on the 10th anniversary of SPARC
(S2) Antarctic Stratospheric Sudden Warming (SSW) in September 2002A total of 96 scientists participated, from 10 countries. The symposium included 21 invited papers and more than 50 contributed papers and posters. Session S1 had been planed in commemoration of the 10th anniversary of SPARC, while session S2 was hastily arranged to discuss the major Antarctic stratospheric sudden warming (SSW) occurred in September 2002. Following is a brief report of each session.
1. Variability of the T-S Coupled System
Various aspects of variability of the T-S coupled system were discussed. In particular, a number of papers dealt with the Arctic Oscillation (AO) and/or the North Atlantic Oscillation (NAO).
K. Hamilton reported GCM experiments on effects of polar vortex perturbations on the tropospheric winter circulation by the use of the GFDL SKYHI model. Y. Kuroda discussed observational results on dynamical coupling of the Polar-night Jet Oscillation (PJO) and AO during the Northern Hemisphere (NH) winter. D. Karoly showed the observational evidence of trends in the Southern Hemisphere (SH) annular mode. Y. Orsolini presented signatures seen in the stratospheric ozone distribution that originated from interannual changes of tropospheric dynamical fields. K. Iwao discussed dynamical contribution to ozone mini holes frequently observed over Europe during winter.
K. Kodera discussed the influence of the stratosphere on the troposphere in connection with AO and NAO on the basis of a GCM experiment. T. Dunkerton discussed the stratospheric vacillation due to the annular mode variability based on model experiments. K. Harada reported on the dynamical linkage of the troposphere and stratosphere in terms of leading mode coupling. A. Ruzmaikin showed the observational evidence of the solar variability influence on the T-S coupling. S. Zhou presented observational evidence of dynamical links of AO and the Madden-Julian Oscillation (MJO).
A. O'Neill discussed the dynamical coupling of the troposphere and stratosphere from a viewpoint of weather forecast improvement. T. Iwasaki presented a new formulation to diagnose the wave-mean flow interaction and discussed the energy cycle. N. Kawamoto showed time variations of the descent rate in the Antarctic vortex based on the ILAS observations. Y. Tomikawa presented observational results of short-period disturbances trapped at the edge of the stratospheric polar vortex. Y. Hio discussed observational results of quasi-periodic variations in the SH stratosphere.
W. Robinson investigated a mechanism for downward influence of the stratosphere on the troposphere by the use of an idealised model. H. Nakamura discussed the linkage of the troposphere and stratosphere due to the propagation of stationary Rossby wave trains. Y. Naito presented the results of a parameter-sweep experiment concerning the effects of the QBO on SSWs. H. Mukougawa spoke on the predictability on recent SSWs on the basis of one-month forecast data of the JMA numerical weather prediction model.
M. Baldwin used an empirical statistical model and discussed extended-range forecasts of the dominant pattern of surface weather variability. M. Taguchi reported on the tropopause valve effect on the troposphere and stratosphere seen in a simplified GCM. K. Yamazaki discussed a possible mechanism of the ozone minimum over the subtropical northwestern Pacific during winter. M. Inatsu discussed atmospheric response to zonal variations in mid-latitude SST by the use of a simplified GCM.. J. Ryoo presented observational features of SSWs based on a composite analysis.
2. UT/LS and Tropical Tropopause Layer (TTL)
J. Holton opened the session as one of the key invited speakers. He introduced a new concept referred as the TTL which has been highlighted in recent years in view of the troposphere-stratosphere exchange and stratospheric dehydration. He emphasized horizontal transport in this layer and performed a simple mechanistic model experiment with an annual variation of the tropopause. Also he mentioned a possible impact of the QBO on water vapour distributions.
M. Shiotani presented results from the SOWER/Pacific campaigns including unique water vapour profiles in the tropics and some comparisons between several hygrometers. M. Niwano found out using the HALOE water vapour and methane data that the inferred ascent rates in the equatorial lower stratosphere show clear seasonal variation with modification by the QBO. H. Takashima utilised the SHADOZ ozonesonde data to investigate ozone variations in the TTL.
S. Pawson addressed issues related to the modelling and assimilation of water vapour in the UT/LS. He also emphasized the importance of appropriate representing physical processes in models. T. Peter focused on ultra-thin tropical tropopause clouds with a vertical thickness of only 100-300 m and stressed their importance for dehydration from the view point of microphysical processes. N. Eguchi showed results from the UARS/MLS upper troposphere water vapour data, focusing on the tropical intraseasonal oscillations.
P. Haynes demonstrated trajectory-based analyses to understand the tropopause region. In the extratropics the distribution of transport timescales from the boundary layer shows an objective contrast between the troposphere and stratosphere. In the tropics, he suggested that the microphysical efficiency of the drying process may be important. H. Hatsushika showed using trajectory analyses that the anticyclonic circulation acts like a spiral staircase crossing the tropical tropopause. J. Suzuki analysed Kelvin wave activity around the tropical tropopause and found its maxima in the Eastern Hemisphere during the solstitial seasons. The first results from the Equatorial Atmosphere Radar (EAR) (Bukit Kototabang, Indonesia) were presented by M. Fujiwara concerning Kelvin wave breaking events and by M. Yamamoto about possible Kelvin-Helmholtz instability.
K. Sato showed results from radiosonde observations through a ship cruise in the Central Pacific. One highlight is a clear evidence of meridional propagation of an inertia-gravity wave generated at ITCZ. S. Dhaka used Indian MST radar to investigate convective updraft by gravity waves (GW) during tropical convective events. Y. Kawatani investigated enhancement of GW activity in the Atlantic Ocean using AGCM simulation. H. Chun used a mechanistic model to discuss the generation mechanism of convectively forced internal GW. T. Horinouchi also discussed convectively generated GW in a numerical experiment including the troposphere, stratosphere and mesosphere.
3. Chemistry-Climate Interaction
J. Austin reviewed difficulties of simulation in chemistry-climate models (CCM) of the stratosphere, and also reviewed assessments of the future ozone hole. The 11-year solar cycle, volcanic aerosol, halogen release, temperature coupling are important to chemistry-climate problem. There is model temperature bias that should be improved to predict PSC area. Ensemble experiments are rather essential, because dynamics is important (e.g., the 2002-year ozone hole).
T. Nagashima discussed the results of ozone hole experiment in the CCSR/NIES CCM. He also discussed less water vapour problem in the model. The model used a nudging method to relax to observed water vapour content. If there is no nudging, short duration of PSC makes insufficient ozone hole. M. Takigawa presented SOX chemistry in the CCSR/NIES CCM and an application to the Pinatubo eruption event. In this event, ozone decrease was well simulated.
Y. Kondo discussed denitrification mechanism. They analysed the removal of HNO3 and the difference between 20 km (decrease) and 15 km (increase). To estimate HNO3 decrease, the ILAS data were used. A box model was also used to check their results. NAT/NAD nucleation is important in the denitrification.
T. Wehr presented ESA atmospheric missions. GOME is still operational. MIPAS, GOMOS, SCIAMACHY, SWIFT projects were discussed. T. Dunkerton proposed a new project of South Asia monsoon and transport experiment.
M. Schoeberl discussed suitability of assimilated meteorological fields for chemical transport. They estimated age spectrum for UKMO DAS winds fields diabatic trajectory, UKMO kinematic trajectory, FVDAS data set, and GCM. H. Akiyoshi discussed nudging Chemical Transport Model for study of ozone change and comparison to ILAS observational data. The model simulates ozone change showed by ILAS in 1997 summer time. NOX chemistry for ozone destruction was also discussed.
A. Ravishankara reviewed the chemistry of ozone and aerosols. He emphasized the need for process understanding to quantify the formation and removal processes of aerosols. V. Ramaswamy discussed temperature changes in the stratosphere and related changes in chemical species.
S1. Special Talks on the 10th Anniversary of SPARC
Two talks were given by M.-L. Chanin and M. Geller, who had been co-chairs of SPARC Scientific Steering Group from the beginning, i.e., March 1992. M.-L. Chanin recollected the efforts to establish the SPARC project in WCRP since late 1980’s. It was the first project “to introduce Chemistry into the fortress of Physics” in WCRP. She also summarised its development phase under three themes: (1) stratospheric processes and their relation to climate, (2) stratospheric indicators of climate change, and (3) modelling stratospheric effects on climate. Her article on the history of the beginning of SPARC will appear in the next SPARC Newsletter.
M. Geller talked on his association with SPARC under the title of “How SPARC has influenced my research”. He gave three examples: (1) finding of the cooling trend of the tropical cold point tropopause temperatures in contrast to the increasing trend of the stratospheric water vapour, (2) analysis of GW activity over the USA with high vertical resolution radiosonde soundings, and (3) modelling total ozone evolution in the past two decades with a CCM. He closed by saying that “if one chooses to spend part of one’s precious time and effort to participate in international programs, such as SPARC, my experience is that you get back not only what you put in but even more in terms of scientific ideas, scientific interactions, and especially long-lasting friendships”.
S2. Antarctic Stratospheric Sudden Warming in September 2002
A special discussion session on the Antarctic SSW events, which occurred in September 2002, was held. S. Yoden showed animations of the daily total ozone fields assimilated at KNMI (http://www.knmi.nl/gome_fd/) and potential vorticity fields at a mid-stratospheric level to characterise the split of the polar vortex. Diagnosis of planetary waves for the past 24 years showed that this is an unprecedented event in September, but similar and weaker events were observed in November in the past. A simple vortex-dynamics model in 2-D can describe the vortex split and remerger, but an extreme condition for the split suggests the importance of stationary wave of zonal wavenumber one.
T. Hirooka described the vertical linkage of the events on the basis of the Met Office stratospheric assimilated data and compared it with another year, 2001 when the usual seasonal march was observed. In 2002, the polar night jet fluctuated rather regularly with a typical time scale of about 10 days throughout the winter. The regular fluctuation of the polar night jet was associated with periodic strengthening of the planetary wave activities of zonal wavenumber 1 and 2, as illustrated by time-height sections of the Eliassen-Palm flux and its divergence. Seasonal march of the polar vortex and planetary wave activity were quite different in 2001 and 2002.
A. O’Neill diagnosed the SSW events with high-resolution PV maps from the Met Office. He also pointed out the occurrence of blocking phenomenon in the upper troposphere and discussed the vertical linkage between the stratosphere and the troposphere. M. Baldwin also discussed the vertical linkage based on the Southern Annular Mode (SAM). He pointed out that the warming event was not only unprecedented in the SH, but the SAM values exceeded those seen in the NH. An event of this magnitude, intensity, and duration has never been observed in either hemisphere.
More details about this event are reported in the issue of this Newsletter (Baldwin et al.).
