The ultralow frequency microbarograph system is described, and some results for periods ranging from a few minutes to a few hours are presented. Problems encountered during operation of the system are also discussed

Herron, T.

Tolstoy, I.

English

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PRECEDI'NG PAGE BLAiNX NOT FILhMED
THE HUDSON LABORATORIES MICROBAROGRAPH SYSTEM:
RESULTS AND FUTURE TRENDS
I. Tolstoy and T. Herron
Hudson Laboratories of Columbia University
Dobbs Ferry, New York 10522
ABSTRACT
An outline of the Hudson Laboratories
Microbarograph system is given, with
mention of some results and problems
for periods ranging from a few minutes
to a few hours.
1. THE HUDSON LABORATORIES MICROBAROGRAPH ARRAY
In late 1965 the development of an ultra-low frequency (10 Hz<f<l Hz)
microbarograph array was undertaken at Hudson Laboratories, Columbia Univer-
sity. Since we desired to include periods up to 90 min or so, we had to make
our own microbarographs. This was done during the fall of 1965 and early
1966, following a design suggested and already partially tested by J. Young
and R. Cook of the ESSA infrasonics groups in Washington, D. C. Since 1966,
the number of sensors operating in the field has varied between 1 and 16,
depending upon the particular experiment being conducted. On the whole, the
system has steadily grown to its present size of 16 microbarographs. A map
showing the distribution of sensors as of spring 1968 is given in Fig. 1.
In addition to the microbarographs, the system includes one Doppler-shift
type ionosounder and magnetometers at the Catskill (New York), Thornhurst
(Pennsylvania), and Lebanon (New Jersey) sites.
All instrument outputs are transmitted by telephone lines to the central
recording station at Hudson Laboratories in Dobbs Ferry. The data are record-
ed in digital form (BCD) on magnetic tape, with a total capacity of 32 chan-
nels capable of recording one four-digit number each twice a second.
2. TYPE OF PHENOMENA INVESTIGATED SO FAR. SOME RESULTS.
Most of the system's work to date has been oriented toward a study of
background pressure fluctuations for periods of 5 min to 90 min, approximate-
ly. Velocities of propagation for naturally occurring disturbances in this
band appear to vary from about 10 m sec-1 to several hundred m sec- 1. The
corresponding wavelengths therefore vary from a few km to 1O km or so. This
scale of dimensions corresponds to what the meteorologists refer to as the
mesoscale, somewhere between meteorological phenomena proper at one end and
boundary layer turbulence and wind effects at the other (micrometeorological
effects, see, e. g., Lumley and Panofsky, 1964). Insofar as the acoustician
is concerned, periods 1 sec<T<lO min are in the infrasonic domain. Periods
T>10 min, when they do correspond to wave phenomena, belong to the internal
gravity wave part of the spectrum.
693
https://ntrs.nasa.gov/search.jsp?R=19720017738 2020-03-23T12:48:23+00:00Z
HUDSON LABORATORIES MICROBAROGRAPH SYSTEM
75 ° 74*
Figure 1. Microbarograph array.
The spectral distribution of the background energy given by our studies
is typified by the average, smoothed, type of behavior shown in Fig. 2. This
particular curve is an average over many weeks of data. It is representative
of hundreds of curves of this type obtained by us over a period of about two
years. It is also consistent with earlier results of Gossard (1960), Golitsyn
(1964), and Pinus et al. (1967).
As a result of studies performed in the summer and fall of 1967, using
the small scale network of microbarographs shown in the inset of Fig. 1, we
have succeeded in showing quite conclusively that much of the energy input
into this band comes from the jet stream (Herron and Tolstoy, 1968; Tolstoy
and Herron, 1968). Thus, for lengthy periods of time (often for weeks on end)
the direction of travel of pressure perturbations in this part of the spec-
trum closely follows that of the jet stream winds aloft. The velocities of
propagation, in the 20-50 m secl are also of the same order. In addition,
a preliminary calculation indicates that the correct order of magnitude for
ground level pressure perturbations, as well as the main spectral character-
istics, are obtained if one assumes that the wind fluctuation power spectrums
obtained from flying aircraft (Kao and Woods, 1964; Reiter, 1963) correspond
to internal gravity wave systems being shed by the jet stream. This shedding
could occur near the core or, as suggested by Claerbout (1967), near the level
of least stability below the core itself. Figure 3 shows a comparison of our
calculation with some of our mean and extremal power spectrums. It is seen
that this mechanism not only yields the correct orders of magnitude for the
pressure fluctuations, but also appears to explain the typical knee appearing
on all pressure power spectrums in this band of periods.
694
I. TOLSTOY AND T. HERRON
PERIOD (MIN)
6
Figure 2. A typical single spec-
trum (24 hour sample) and a month-
ly mean power spectrum for back-
ground pressure fluctuations at
Hudson Laboratories.
e,
a
=L
.4
CD
0 2W
U:
la,
.- I
0.1
GROUND LEVEL
1 10
FREQUENCY (C/H)
PRESSURE POWER SPECTRUM
6
5
Figure 3. Comparison of mean and
smoothed extremum power spectra
for pressure with calculated power
spectra, based upon a simplified
mechanism of internal gravity wave
generation by the jet stream, for
two different assumptions for the
stream velocity (dashed lines).
z 4
A
5 3
o 2
CALCULATED FROM JET
STREAM FLUCTUATION
SPECTRUM OF KAO AND WOODS
40SEC- 
20 m SEC-'
-- MIN SMOOTHED
0 0.1 I 10 100
f CPH
I I I I I I I
120 6030 15 10 5 2.5
T (MIN)
695
I_ 
HUDSON LABORATORIES MICROBAROGRAPH SYSTEM
3. SOME FURTHER PROBLEMS TO BE INVESTIGATED
Insofar as larger-scale phenomena are concerned, the use of beam forming
techniques on the full array of Figure 1 indicates the existence of disturb-
ances having periods of 15 to 50 min, traveling at speeds of the order of
300 m sec-1 . A systematic study of these processes is underway. If this is
a wave phenomenon, as appears probable, then one is dealing with internal
gravity waves of wavelengths between 300 and 1000 km.
Apart from long wavelength internal gravity waves of this type and short
wavelength ones of the kind generated by the jet stream, there exist other
processes for the propagation of pressure disturbances in the mesoscale range.
Obvious candidates are wind-borne convection systems, large-scale eddies, etc.
There is also another fairly obvious wave phenomenon, i.e., that of stability
(or instability!) waves in shear flows. This type of disturbance is well
known to hydrodynamical theorists (see, e.g., Lin, 1955). Clearly the tropo-
spheric wind system which culminates in the jet stream at 10 km altitude
represents a steady shear flow capable of supporting waves of this kind. A
more thorough theoretical and experimental study of the relevance of these
waves is desirable.
ACKNOWLEDGMENTS
This work was supported by the Office of Naval Research and the Advanced
Research Projects Agency under Contract Nonr-266(84). Reproduction in whole
or in part is permitted for any purpose of the United States Government. It
is Hudson Laboratories of Columbia University Contribution No. 327.
REFERENCES
Lumley, J. L., and H. A. Panofsky, 1964: The Structure of Atmospheric Turbu-
lence. New York, Interscience Publishers, 239 p.
Gossard, E. E., 1960: Spectra of atmospheric scalars. J. Geophys. Res., 65,
3339-3351.
Golitsyn, G. S., 1964: On the time spectrum of micropulsations in atmospheric
pressure. Izv. Geophys. Ser., 8, 1253.
Pinus, N. Z., E. R. Reiter, G. N. Shur, and N. K. Vinnichenko, 1967: Power
spectra of turbulence in the free atmosphere. Tellus, 19(2), 206.
Herron, T. J., and I. Tolstoy, 1968: Tracking jet stream winds from ground
level pressure signals. J. Atmos. Sci., in Press.
Tolstoy, I., and T. J. Herron, 1968: A model for atmospheric pressure
fluctuations in the mesoscale range. J. Atmos. Sci., in Press.
Kao, S. K., and H. D. Woods, 1964: Energy spectra of mesoscale turbulence
along and across the jet stream. J. Atmos. Sci., 21, 513.
Reiter, E., 1963: Jet-Stream Meteorology. U. of Chicago Press, 515 p.
Claerbout, J. F., 1967: Electromagnetic Effects of Atmospheric Gravity
Waves. Massachusetts Institute of Technology thesis.
Lin, C. C., 1955: The Theory of Hydrodynamic Stability. Cambridge U. Press,
155 p.
696
AUTHOR INDEX
Aarons, J.
Astheimer, R. W.
Atlas, D.
Bandeen, W. R.
Barrett, E. W.
Beard, C. I.
Birkemeier, W. P. .
Chahine, M. T.
Clemesha, B. R.
Collis, R. T. H.
Cook, R. K.
Cox, D. C.
Decker, M. T.
Deitz, P. H.
Donn, W. L.
Fox, H. L.
Fried, D. L.
Fritz, S.
Godson, W. L.
Grams, G.
Hablutzel, B. C.
Hardy, K. R.
Harp, J. C.
Herron, T.
Hufnagel, R. E.
Ishimaru, A.
697
89
517
245
465
173
79
337
443
201
147
633
295
397
119
681
671
133
507
511
207
555
217
21
693
145
87
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Kaplan, L. D. . . . 435
Kasemir, H. W. . . . . . . . . . . 617
Katz, I. . . . . 217
Kessler, E . . . 287
Kieburtz, R. E. . . . . . . 367
King, J. I. F. . . 453
Krause, F. R. . . 555
Lawrence, R. S.
Lee, R. W.
Lhermitte, R. M.
Little, C. G.
Lucy, R. F.
91
21
253
619
125
Marshall, J. S.
Montgomery, A. J.
291
525
Pierce, E. T. .
Portman, D. . .
Posmentier, E. S . .
Reagan, J. A.
595
111
681
213
Sandborn, V. A.
Schotland, R. M.
Staelin, D. H.
Strohbehn, J. W.
589
179
409
1
Tolstoy, I. 693
Welch, W. J.
Westwater, E. R.
Wheelon, A. D.
369
397
359
698
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The Hudson Laboratories microbarograph system: Results and future trends

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