by Sietse Dijkstra, Robert Haas, Casper ter Kuile, Koen Miskotte, Jos Nijland, Arnold Tukkers and Michel Vandeputte
Jin Zhu, Xiaojun Jiang, Bin Yang, Huan Meng, Dan Xia, Xuefei Gong, Haitao Chen, Min Guan, Wenzhong Liu, Jian Gao, Rui Qi, Yongming Chen
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Overview of weather forecasts for China, Xinglong area, for november 18, 2001, at the time of the Leonid maximum. |
Senior meteorologist at the Royal Netherlands Meteorological Institute.
Forecast issued at: 13 november 2001, 06:24 UT
Dear Dr. Zhu,
First one remark before I write my bulletin: Weatherforecasts for a certain moment, provided 4 days ahead, are sometimes quite easy changing in the course of that same forecastperiod if you look at the updates. At this moment I have looked at the weathermaps of the global computermodel. I have looked in detail to the groundpressure in your area, to the amount of moist in several layers of the atmosphere, and to the winddirections in several layers.
This is my conclusion for the 18th of Nov, based on the computerseries of Nov. 12 th: The area of Xing Long will be situated in the vicinity of high pressure with a centre just to the west on the mainland of China. In a Northwesterly flow, quite dry air will be advected in almost every layer (from surface up to 300 hpa (9 km)). If this situation would turn out to be reality I expect fairly good meteor-watching conditions. One problem is that there is some haze in the lowest levels with this high over the area. Higher in the mountains you will have no problem with that stuff. Again I have to emphasise that this is a very preliminary forecast, almost 120 hrs ahead. Do not act to strong on this vision. I will update my forecast in the coming days, I hope once every 24 hrs.
Dr. Zhu, I hope that you will give the contents of this e-mail to my Dutch fellows and that it will help you a bit in planning the action.
Thanks for delivering the information to them.
Regards,
Jacob Kuiper
Senior meteorologist Royal Netherlands Meteorological Institute.
Forecast issued at: 14 november 2001, 17:59 UT
Dear Dr. Zhu,
Here the new forecast.
The general pressuredistribution for Nov 18th to 19th has NOT changed a lot. The high pressure is still present on the mainland of China with a northwesterly flow over the Xing Long area. Again the moisture in all layers is low so I expect hardly any clouds for that time.
Tomorrowmorning, around noon Dutch time (somewhere around 19 o-clock local China time) I will update my forecast for you.
Regards,
Jacob Kuiper.
Forecast issued at: 15 november 2001, 16:51 UT
Message with 3rd weatherforecast for Dr Jin Zhu and his Dutch Meteor group.
Dear Dr. Zhu,
Again there has been some delay in sending you a weather-forecast for the Leonid period. This was partly because a very bright Leonid-fireball has crossed the sky in the Netherlands this morning. Lots of people have phoned the Meteorological Office and some colleagues of the public relations department asked me to explain what all eyewitnesses could have seen. So, a lot of media-attention by this event in the Netherlands.
I have looked now to the weathermaps of the global computermodel. Just like the previous forecast also this one is an optimistic one for your area. The high is still present and the flow is still from the northwest. On the evening (Chines local time) of the 19th Nov however a weak trough or front is moving north of your area to the Korean Peninsula, probably accompanied by some cloudsheets in the higher levels.
Because this is quite a long time after the peak of the Leonids I expect that during the main peakperiod from 18 Nov 10 UTC to 19 UTC (the period with the two peaks), there are hardly any clouds in your region. I hope that in the coming days, this nice forecast will turn out to be a persistent one. Coming days I hope to send the forecast again. Due to the enormous busy 'press'-talks here in the Netherlands I cannot promise when these forecasts will be sent exactly, I am sorry for that but I hope you will understand my problem.
Regards,
Jacob Kuiper.
Forecast issued at: 16 november 2001, 12:55 UT
Dear Dr. Zhu,
Again I have watched large amounts of meteorological information.
For your area the general weathersituation has not changed very much. Still the North to Nortwesterly flow is advecting dry air in most levels. So I expect no big problems in the forecastperiod.
In the next 24 to 30 hours I will not be able to provide you some new forecast. At Saturday 17 th Nov, around 18 UTC I will I will send a forecast to you again.
Regards,
Jacob Kuiper.
Forecast issued at: 17 november 2001, 21:55 UT
Dear Dr. Zhu, and the other people from the BENELUX.
For your area the general weathersituation has not changed very much. Still the North to Nortwesterly flow is advecting dry air in most levels in most of the period. So I expect no big problems in the forecastperiod.
In the later part of Nov 19th some cloudsheets from the north or northwest are approaching your area. I think this stuff will not be in time for disturbing the main-peak moment of the Leonids.
I will send a forecast in the course of November 18th around 14 UTC, it is then around 22.00 hours local China time, to you again.
Regards,
Jacob Kuiper.
Forecast issued at: 18 november 2001, 15:04 UT
Dear Dr. Zhu, and the other people from the BENELUX.
For your area now the last weatherforecast for the big-peak moment!
The general weathersituation has not changed very much, but some smaller cloudsheets have reached the area just north or west of Xing Long. Probably you have seen these cloudsheets already passing over the area. I think these clouds will move quite fast further south and will not problemize the situation for the Leonid-peak.
On the latest satellite-images I saw that there are hardly any new clouds behind the actual ones, so a reasonable sky is forecasted for this night. The smoglayer is probably there. I have looked at the radiosoundings of Beying and there I saw that the top of the ground-inversion was around 1000 meters. So all the haze and dust would be concentrated in this lowest layer, above it, it will be clear and clean.
I wish you and my Dutch (and one Belgian) colleagues all the best now and hopefully you all will see a magnificent display of the Leonids 2001.
Regards,
Jacob Kuiper.
