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Ionospheric Reflections and Weather Forecasting for Eastern China*

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Ionospheric Reflections and Weather Forecasting for Eastern China* Ionospheric Reflections and Weather Forecasting for Eastern China* REV. E. GHERZI, S.J. Director for Meteorology and Seismology, Zi Ka Wei Observatory, Shanghai, China HE FOLLOWING LINES describe some Another detail of our technique was that T very interesting and practical results we reduced to 20 watts or less the power obtained at the Zi Ka Wei Observa- radiated by our Hertz aerial, in order to get tory during the past five years, by means of reflections only from a well-ionized layer. the usual ionospheric radio soundings which This frequency of 6000 kc was used con- give the heights of the well-known E and F stantly during all these five years of research, layers. As early as 1936, Martin and Pulley and as we had at our disposal a file of (of the Radio Research Board, Melbourne) synoptic maps from our weather service, we reported on a "Correlation of conditions in quickly noticed a very interesting coincidence the ionosphere with barometric pressure at between the presence of an E or an F, or an the ground.,M We thought this idea very F2 echo, and the air mass which was "domi- interesting and started research along that nating the weather"! Namely, we found line. We wanted to find out if the motions that: (1) every time the Pacific trade-wind of the different air masses which produce air mass which was causing the weather, we the weather of our regions could be corre- had the E-layer reflection; (2) every time lated with the results obtained by the usual the Siberian air mass was dominating the ionospheric sounding technique. As all me- weather, we had the F-layer reflection; (3) teorologists know, once the synoptic weather and in most cases, when Tropical air was chart is plotted, one next asks what air making the weather, we had the F2-layer re- mass is "dominating the weather,'1 for with flection. And this extraordinary coincidence that information the numerous meteorologi- was noticed all year long without any corre- cal data available can immediately be inter- lation to the seasons or the months. Of preted for forecasting the coming weather. course in this region these air masses are Of course, the tendency of barometer, the prevalent according to the seasons, but very isallobars, etc., have been a help for such often the change (over one or two days) in work; but one must admit that many, too the air mass over us was immediately de- many, times, in regions where they indicated tected by the type of the echo from the 2 the pressure should decrease, e.g., the ionosphere! weather elements behaved in a quite differ- Anyhow, every time we had an E reflection ent way than anticipated. we arranged our forecasts of the coming Our ionospheric technique, which has given weather to correspond with the tliermody- namical properties of the Pacific Ocean air good results, will now be described:— mass and when the F-layer reflection oc- We remember that of the E-layer reflec- curred we assumed the Siberian air mass tions there is a class which has been called would be or continue active. The effective- "sporadic," a word that implies we do not ness of such weather forecasts was almost know why they happen, t We chose for our always excellent. pulses (twenty-thousandth of a second) a Of course this sort of forecast is made in frequency which would not give the normal terms of what the Germans have named the E reflections, namely 6000 kc. As far as we large-scale weather pattern ("Grosswetter" had been able to find in publications, echoes of Prof. Baur). Nevertheless, we think obtained from the E layer on such a fre- that if such ionospheric equipment were put quency were usually called "sporadic." into many different weather stations one * This report was submitted for Father Gherzi by 2 This parallels the observations of Ross Hull and courtesy of Commdr. W. J. Dimitrijevic, U.S.N. Pierce in this country during the 1930's published 1 Radio Res. Bd. Rept. No. 11. from time to time in QST. Also, recently Abbot has t See article by Wells in Trans. Amer. Geophys. Un., correlated critical frequencies of the E layer with tem- vol. 26, no. 3, Dec. 1945, pp. 381-388, for latest stud- perature departures at Washington (Smith. Misc. Coll., ies on sporadic E-layer.—Ed. July 1945).—Ed. Unauthenticated | Downloaded 09/26/21 10:47 PM UTC might even use it for a detailed local weather discontinuity layers between the overlying forecast. air masses can reflect or refract downward It would be very interesting to see if, in a part of the energy of the radio pulse and the United States, where the leading air so show the vertical structure of the tropo- masses are similar to those in China, the sphere; a fact that we for many years have same striking coincidence is found.2 We used in our weather work. As the spiralling would think that with polar air acting over column of a typhoon is usually not higher the eastern States the F-layer reflection than 2 to 4 or rarely 6 km (in 1935 we had should be obtained, while, when tropical At- planes following our advice and flying safely lantic air is prevailing, then the E-layer re- above the cyclone at 4 km height), there is flection should be seen, and with the Gulf in front of the storm a very abundant accu- air mass advancing the F2-layer reflection mulation of rain, which is blown away hori- should be present. However, for the F2- zontally from the top of the cyclonic column layer reflections, things are not as clear-cut by the driving Pacific air mass at that limit- as for the other layers. ing height of around 3 km. Consequently a We must add that these soundings were radio pulse will be strongly reflected down- made in day time and not at night nor at ward when striking that kind of extended sunrise and sunset. It is only when the iono- frontal upper-border; of the typhoon. If the sphere is, so to say, stabilized over the lo- center of the storm should pass just over our cality that this interesting and useful coinci- locality that reflection will be shown. In dence appears. case this reflexion is not found that means As a rule only one type of echo is apparent that the cyclone can very well be strongly on the screen although multiple reflections felt but the center itself will pass some dis- tance from the place where the radio meas- of the same echo are often present (E, E3, urement is being made. The cases we were E2, etc.), when the action of the correspond- ing air mass will be more intense. At times able to check were all positive and our fore- both kinds of echoes are seen and then it casts proved to be correct. becomes very interesting to notice which one These results, which perhaps are already is the stronger as that may help to decide known (we have received no scientific publi- which one of the two air masses, which are cations since the end of 1940!), have greatly still in "conflict," will "overpower" the helped the work of our weather service. other. When a northerly gale is threatening Nevertheless, it remains to discover the owing to a very rapid advance of Siberian physical cause of these striking coincidences air the F reflections become very strong and which point to a kind of "steering" of the the multiples of this echo saturate the screen. lower atmosphere (troposphere) by the In the case of a typhoon heading towards stratosphere (or better, the ionized layers).4 our region the E echo becomes very strong We admit that at present we are unable and lasts several days, and when it decreases to explain all that we have found. How- in intensity we feel that the Pacific air mass ever, if these remarks are interesting and is receding eastward and the cyclone, which possibly new to my readers, it might be ad- is advancing along the border of this air visable for other weather services to start mass (as the isobars drawn for the 3000-m similar research and find out the reasons for level show), will gradually recurve northward such a connexion between the ionized layers and northeastward. and the tropospheric air-mass distribution. A quite successful use of these radio A final remark concerns the possibility of pulses for detecting whether a typhoon will drawing a rough but sufficiently correct map strike our locality was made. As several re- of the disposition of the air masses, by means search people have already shown (e.g., of the "fading" effect so well known to all Friend and Colwell, Proc. of the I.B.E., Oct. people interested in radio. By listening, and 1939),3 the water droplets existing near the 4 See the papers by Wulf, Terr. Magn. and Atmos. 3 See Bull. Amer. Met. Soc., v. 22, Feb. 1941, pp. Electr., Sept. and Dec. 1945, pp. 185-197, 259-278. 53-60.—Ed. —Ed. Unauthenticated | Downloaded 09/26/21 10:47 PM UTC checking on the cathode-ray oscillograph, with the synoptic weather map, we found land and crystal-controlled transmitting sta- that the similarity of the main outlines was tions around a similar frequency (e.g., be- quite satisfactory. Namely, one could learn tween 6000 and 4000 kc) when the sun is by this 1 'fading" method whether this or already rather high above the horizon, one that region was under the same air mass, can group the stations which show a similar and e.g., for flying from Shanghai to Peking type of fading.
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