15:45 〜 16:00
[PEM09-20] Recent progress on observation of noctilucent clouds in middle latitude region
★Invited Papers
キーワード：夜光雲、中間圏、超高層大気、地球温暖化
This presentation reviews the recent progress of NLC observation in middle latitude regions by using ground imagers, airline jets, small balloons, and satellites.
Noctilucent clouds (NLCs) are the highest clouds on the Earth which appear in a mesopause region during the summer season in both sub-polar regions. Since their occurrence is highly sensitive to the mixing ratio of the water vapor and atmospheric temperature in the mesopause region, NLCs are considered to be one of the proxies to monitor the global atmospheric variations. Several models predict that global warming in the lower atmosphere caused by the global increase of greenhouse gasses promotes cooling of the upper atmosphere. In addition, photochemical reactions involving greenhouse gasses such as CH4 would increase the mixing ratio of water vapor which is a source of water ice clouds (NLCs). Thus, enhancement of global warming due to greenhouse gasses can extend the NLC region towards lower latitudes than current typical latitudes (50-60 degrees in latitude). Due to this reason, it is important to know the precise occurrence of NLC in the mid-latitudes region to monitor the progress of global warming. The Japanese research group started NLC observation from the ground in the northern area of Japan, Hokkaido since 2012. They have reported the first detection of NLC from multiple sites in Hokkaido (43.17N-45.36N) Japan on June 21, 2015 [Suzuki et al., 2016]. Although this event is the first “visual” detection of NLC in Japan, radar observations sometimes detected mesospheric echoes (MSE) which closely relate with NLCs before 2015. One of the possible causes which makes this discrepancy in detection frequency between the two methods is poor weather conditions during the early summer season in Japan. A comparison between past NLC periods (summer season) and records of sky conditions in the northernmost part of Hokkaido (Wakkanai) archived by Japan Meteorological Agency shows that only 10.8% (3.1%) of the morning (night) twilight times were clear on the days of MSE events from 2009 to 2015. It is highly desired to monitor the precise occurrence of NLC in the middle latitude region without interruption by poor weather conditions.
Therefore, we conducted NLCs observation by using airline jets in the northern hemispheric summer of 2019, and by small threaded balloons on August 2020 in Hokkaido followed by current ground-based imagers. We also developed an automatic NLC alert system on SNS (Twitter) which notices the current latitudinal distribution of NLCs monitored by Geostationary-Earth-Orbit (GEO) meteorological satellite, Himawari-8 to followers.
Noctilucent clouds (NLCs) are the highest clouds on the Earth which appear in a mesopause region during the summer season in both sub-polar regions. Since their occurrence is highly sensitive to the mixing ratio of the water vapor and atmospheric temperature in the mesopause region, NLCs are considered to be one of the proxies to monitor the global atmospheric variations. Several models predict that global warming in the lower atmosphere caused by the global increase of greenhouse gasses promotes cooling of the upper atmosphere. In addition, photochemical reactions involving greenhouse gasses such as CH4 would increase the mixing ratio of water vapor which is a source of water ice clouds (NLCs). Thus, enhancement of global warming due to greenhouse gasses can extend the NLC region towards lower latitudes than current typical latitudes (50-60 degrees in latitude). Due to this reason, it is important to know the precise occurrence of NLC in the mid-latitudes region to monitor the progress of global warming. The Japanese research group started NLC observation from the ground in the northern area of Japan, Hokkaido since 2012. They have reported the first detection of NLC from multiple sites in Hokkaido (43.17N-45.36N) Japan on June 21, 2015 [Suzuki et al., 2016]. Although this event is the first “visual” detection of NLC in Japan, radar observations sometimes detected mesospheric echoes (MSE) which closely relate with NLCs before 2015. One of the possible causes which makes this discrepancy in detection frequency between the two methods is poor weather conditions during the early summer season in Japan. A comparison between past NLC periods (summer season) and records of sky conditions in the northernmost part of Hokkaido (Wakkanai) archived by Japan Meteorological Agency shows that only 10.8% (3.1%) of the morning (night) twilight times were clear on the days of MSE events from 2009 to 2015. It is highly desired to monitor the precise occurrence of NLC in the middle latitude region without interruption by poor weather conditions.
Therefore, we conducted NLCs observation by using airline jets in the northern hemispheric summer of 2019, and by small threaded balloons on August 2020 in Hokkaido followed by current ground-based imagers. We also developed an automatic NLC alert system on SNS (Twitter) which notices the current latitudinal distribution of NLCs monitored by Geostationary-Earth-Orbit (GEO) meteorological satellite, Himawari-8 to followers.