THE UPPER AIR." By E. GOLD and W. A. HARWOOD. The past decade has been very fruitful in the investigation of the upper air. By the use of kites sufficient results have been obtained to furnish a tolerably complete knowledge of the variation in the meteorological elements up to a height of 2 kilometers, while registering balloons have furnished information regarding the distribution of temperature up to heights of 15 to 20 kilometers. The results of the Berlin manned balloon ascents were arranged and discussed very fully ten years ago, but no such comprehensive discussion of the much more numerous kite and registering balloon ascents has yet been attempted. The present report deals with the instruments and methods of investigation, and with the results for temperature and for wind." The most important series of the earlier ascents with manned balloons was that made by Glaisher in 1860-1870. Unfortunately he was led to believe that artificial ventilation of the thermometers was unnecessary, with the result that his observations at great altitudes are untrustworthy. In the series of ascents made from Berlin in 1888-1895 observations made with careful ventilation proved beyond doubt that large errors would arise in the absence of proper ventilation, and that Glaisher's results were almost certainly affected by such errors. a Report on the present state of our knowledge of the upper atmosphere as obtained by the use of kites, balloons, and pilot balloons. Report of the committee, consisting of Messrs. E. Gold and W. A. Harwood, presented at the Winnipeg meeting of the British Association, 1909. Reprinted by permission from Nature, London, No. 2089, vol. 82, Nov. 11, 1909. The full report of the committee is printed in an octavo pamphlet of 54 pages, with diagrams and tabulated observations, and gives an interesting historical review of the upper atmosphere investigations since 1784. The following table shows the nature of the errors, and incidentally furnishes a comparison with one of the earlier ballon-sonde ascents: Temperature observations in manned balloons are now usually taken with an Assmann's aspirator, in which a ventilating current of about 4 m. p. s. is forced by a fan through a polished tube containing the thermometer and screening it from radiation. The instruments used with registering balloons are of two types. In the large type the record is made on a metal or photographic sheet, covered with lampblack, and wrapped round a revolving cylinder driven by a clock. Pressure, temperature, and humidity are recorded by separate pens. The barometer is a Bourdon tube or an aneroid, the thermometer some form of bimetallic instrument, and the hygrometer a bundle of hairs. In the small type the temperature record is traced on a cylinder or plate, which is itself moved at right angles to the direction of motion of the temperature lever by the changes of pressure. The temperature and pressure are then given by the ordinates and abscissæ of the trace obtained. The advantage of this arrangement is that no clock is required, and the instrument can be made much lighter and is more easily tested. The loss of the humidity trace is unimportant, because the hygrometric records at low temperatures are very untrustworthy, and the observations in the lower layers can be made with kites or manned balloons. The instruments used with kites are similar to the ballon-sonde instruments of the larger type, but they have an arrangement for recording wind velocity. In the Dines instrument the records are traced on a flat, circular sheet of cardboard rotated by means of a clock and resting on a wooden tray beneath which the instruments are placed. The ballon-sonde instruments are tested either (1) by keeping the thermometer at ordinary atmospheric pressure in testing for temperature and the barometer at ordinary temperatures in testing for pres sures, or (2) by testing the thermometer through the temperature range at different pressures and the barometer through the pressure range at different temperatures. The second is, of course, the more desirable plan, but the difficulties involved in applying it to the larger type of instrument are so considerable that the former method is generally adopted where such instruments are used. The simplicity of the smaller type of instrument devised by Dines enables the second method to be adopted in testing it without elaborate and expensive apparatus. Temperature records obtained simultaneously with different instruments show differences which, in the mean, do not exceed 1° C., and the temperatures may, in general, be taken to be correct to this degree of accuracy, but lagging of the instruments makes it doubtful if in all cases the recorded temperatures and heights actually correspond. In dealing with the observations it is found convenient to express temperatures in degrees centigrade above the absolute zero, -273° C. on the ordinary scale. Where necessary the letter A is used to characterize this scale. Atmospheric temperatures, both at the surface and in the upper air, lie almost always between 200° A and 300° A, so that the 2 may be dropped without risk of confusion. Gradients of temperature are expressed in degrees centigrade per kilometer, and are reckoned when temperature decreases upward. The mean value of the gradient up to 3 kilometers is as follows: From the Berlin manned balloon ascents, 1888-1897- Degrees. 5.1 4.8 4.7 5.7 It follows from these results that the mountains are colder than the free atmosphere at the same height, and maney observers have verified this fact by direct comparison. Shaw and Dines found that in July, 1902, the temperature on Ben Nevis was 2.6° C. below that of the free atmosphere at the same height to the west of the mountain. Schmauss found that the temperature on Zugspitze (nearly 3,000 meters), which lies on the northern edge of a mountainous region, was continually lower than that of the free atmosphere, but was higher than that at the same height on Sonnblick, which lies in the middle of the Alps. It was pointed out by Von Bezold that increase of temperature on a mountain is limited by convection, whereas no immediate limit is set in this way to cooling. There is a one-sidedness in the heat exchange between the mountain surface and the atmosphere which would tend to produce the result found by observation. Moreover, convection always tends to raise the temperature of the upper air above what it would be otherwise, and in addition the cold of winter is, as it were, stored up in the snow, while no such process holds for 45745°- -SM 1909-18 the warmth of summer. Both conditions are probably effective in increasing the temperature difference. The most important deduction to be made from the results is that the mountains are not cold because the upper air is cooled by convection, but they are cooled by their radiation to space. The mean values of the gradients up to 15 kilometers, found from registering balloon ascents at ten European stations and for St. Louis, Mo., are given in the table: The maximum value occurs in the layer 7 to 8 kilometers, and its magnitude indicates that the effect of radiation is to leave practically unchanged the natural gradient in air in vertical motion. Gold showed that in the upper layers absorption exceeded radiation and in the lower layers radiation exceeded absorption, and both processes would diminish the temperature gradient. At an intermediate stage absorption and radiation must balance, and the results indicate that this is the case at a height of 7 to 8 kilometers. The temperature at different heights up to 15 kilometers shows practically no variation for the ten European stations, except in the case of Pavlovsk, where the temperature is uniformly lower up to 10 kilometers and higher above 10 kilometers than at the other stations. The difference of temperature between Strassburg and Pavlovsk, taken to represent latitude 50° and latitude 60°, respectively, is sufficient to produce a gradient of pressure at a height of 10 kilometers which would correspond to a steady west wind of about 24 m. p. s. (54 miles per hour). The difference between Strassburg and St. Louis (representing latitude 39°) would at the same height correspond to a steady west wind of 15 m. p. s. in intermediate latitudes. The observations are not sufficiently extensive to warrant much stress being laid on the absolute values of these velocities, but it is of interest to note that the approximate ratio of the west winds in latitudes 45°, 55°, deduced from Oberbeck's solution by a purely theoretical treatment of the problem of the general circulation, is 16/21 for the upper strata, a result in tolerable agreement with the ratio of 15/24 deduced from the temperature observations. The problem of the vertical distribution of temperature in cyclones and anticyclones depends for its solution on upper-air observations. Hann deduced from the temperatures at high-level observatories that cyclones were colder than anticyclones, the mean difference of temperature up to 3.5 kilometers being as much as 5° C. Grenander found similar results by a consideration of the kite and balloon ascents at Hald and Berlin, while Von Bezold deduced from the Berlin manned balloon ascents that the relative coldness of the cyclone was maintained even up to 8 kilometers. The results in the present report, obtained by taking only those cases in which the sea-level pressure exceeded 770 millimeters or was less than 750 millimeters, and correcting the observations for seasonal and local variations, showed that the cyclone was colder than the anticyclone up to 9 kilometers, while at greater heights the conditions were reversed, and the anticyclone became much colder than the cyclone; but the effect of the temperature difference in the lower layers on the pressure difference is so considerable that even at 14 kilometers the pressure gradient is not reversed. In these circumstances it is difficult to see how air can be brought into the anticyclonic and out of the cyclonic regions in the upper air. The cirrus observations imply a definite outward motion over cyclonic regions, but a rotation in the same direction as at the surface, which can be the case only if the gradient of pressure is also in the same direction as at the surface. These results imply that there is motion across the isobars from the lower to the higher pressure. Now, although it is possible for such motion to exist if the velocity in the cyclonic region exceeds a certain value, or, in the anticyclonic region, lies between certain limits, it is not possible to have steady motion of this type, and the effect of damping would be to make the motion from the higher to the lower pressure. The evidence points to the conclusion either (1) that cyclones and anticyclones arriving in the European area are in general dissipating systems which are continually replaced by other systems arriving from what may be called productive regions, or (2) that there is interchange of air with regions in which the surface temperature or the temperature gradient differs sufficiently to produce mean temperatures greater in low-pressure areas and less in high-pressure areas than are found over Europe. It is interesting in connection with this part of the subject to note that Shaw and Lempfert deduced from a discussion of surface air currents that the central areas of anticyclones were not the regions of origin of currents, and could not, therefore, be places where descent of air was taking place to any considerable extent. The temperature observations in the first 3 kilometers agree with this conclusion, since they show that there is no approach to a regular adiabatic gradient near the centers of anticyclones. |