Survey of cosmic-ray intensity in the lower atmosphere

Section: Resultsmentioning

confidence: 99%

Barometric coefficients of multiplicities in neutron monitors

Hatton¹,

Griffiths²

1968

“…If it has to fit in with the conventional definition of the theoretical cosmic ray equator, it should be defined as the line around the surface of the Earth which connects the points where the minimum counting rates of a cosmic ray detector with a very high counting rate occur during equatorial crossings along straight-line routes exactly in a north-south direction. In practice, however, the position of the experimental cosmic ray equator was determined by fitting a second-degree polynomial in latitude through the data points of routes crossing the equator in directions not necessarily perpendicular to the geographic equator [e.g., Simpson et al, 1956;Pomerantz et al, 1960;Coxell et al, 1966]. We prefer to use the term experimental routedependent cosmic ray equator for equatorial locations ob- tained by this method.…”

Section: Experimental Cosmic Ray Equatormentioning

confidence: 99%

Secular changes in the cosmic ray equator

Walt¹,

Stoker²

1990

Since the cutoff rigidity at the cosmic ray equator varies with longitude, the location of the minimum cosmic ray intensity obtained during a latitude survey depends on the direction by which the geographic equator is crossed. A method is developed to compare the location of the recorded minimum cosmic ray intensity with that of the predicted minimum along a route as calculated from cutoff rigidities. The data of several surveys, covering the period 1954–1986/1987, are used. Instead of the accurate but computer intensive trajectory‐tracing method, cutoff rigidities for every location and instant are interpolated from 5°×15° world grids. It is found that the positions of the minima in cosmic ray intensities obtained from a survey across the equator and those derived from the interpolated cutoff rigidities along the survey route are mutually consistent. The rms difference between the experimental and calculated positions of the cosmic ray minima for all the surveys amounts to only 0.32°. Major secular changes in cutoff rigidities occur in the Atlantic Ocean region. Whereas a fast northerly shift of the cosmic ray equator is evident between 320° and 345° longitude, the data points from different epochs within this longitude range show a negligible difference between the simulated and experimental positions of the route‐dependent cosmic ray equator. This indicates that the secular variation in cutoff rigidity is well accounted for by the grid values derived from the International Geomagnetic Reference Fields for 1955.0, 1965.0, and 1980.0, even when the values are extrapolated linearly beyond 1980.0 through to 1987 in equatorial regions.

“…As shown in Figure 3, the observed distribution of intensity of the nucleonie component confirms the general accuracy of the contempo-rary method of determining threshold rigidities. An isocosm map [Coxell et al, 1966] displays the data in a form that facilitates comparison of the theoretical predictions and measurements in different geographical regions. In Figure 7 the data symbols represent a specific intensity chosen according to the method described by Pomerantz and Agarwal [1962] dN,(P, x, t) djz(P, t) (1) dP --•" S,z(P, x) dP where dNi(P, x, t) dP is the differential response for multiplicity i, rigidity P, atmospheric depth x, and time t; S,, is the specific yield function for incident primaries of charge z, and t) dP is the differential primary spectrum.…”

Section: Isoc0smsmentioning

confidence: 99%

Cosmic ray intensity variations in the lower atmosphere

Kent¹,

Pomerantz²

1971

Self Cite

Worldwide cosmic ray intensity measurements at aircraft altitudes have been made over a solar cycle. Data obtained with a neutron monitor aboard the U.S. Naval Oceanographic Office Project Magnet aircraft during different epochs have been compared to determine the long‐term variation of the nucleonic intensity at latitudes ranging from north to south geomagnetic poles. The measurements were normalized to a constant pressure‐altitude, 500 mm of Hg, on the basis of experimentally determined time‐ and rigidity‐dependent attenuation coefficients. Between October 1958 and January 1965, the intensity increased 8.7% at a rigidity of 17 Gv, and 20.9% at 2 Gv. The measured intensities as a function of threshold rigidity are in good agreement with the predictions of trajectory calculations based on a sixth‐degree simulation of the geomagnetic field. At solar minimum, measurements of the latitude effect were also obtained for five groups of multiple events and for mesons; the highest group, multiplicity K≥6, varies less with latitude than do the mesons. The latitude effect for K=3 is intermediate between that for the neutron total counting rate and the meson counting rate. The attenuation length for mesons is found to vary with altitude in reasonable agreement with the predictions of Wada [1960].