IGY Bulletin, Number 7, January 1958 - Rocket Flare Patrol Program

This next article in the IGY Bulletin points out that several rockets were launched in July and August of 1957 to collect data on solar X-rays during times of solar flares. These missions were part of the Rocket Flare Patrol Program. (I can't find ANY links for this program online!)

I've mentioned solar flares in this previous post and this one also.

Here is a short NASA video tutorial on solar flares:

The Rocket Flare Patrol Program was designed to learn more about radio fadeouts caused by solar flares. Thirteen DAN program rocket flights that were sent up after solar flares were observed are listed in the Bulletin article. Altitudes ranged from 2 to 50 miles above the Earth's surface. The article goes on to describe some of the underlying ionospheric physics, rocket technology, and early results of this program, although I won't delve into these details. The program was conducted by the Naval Research Lab directed by the eminent physicist and space scientist Herbert Friedman; this blog post from the American Philosophical Society Library summarizes his scientific accomplishments as well as discussing the conservation of some of his medals in the collections of the APS.

According to this web page from the Stanford Solar Center, the Earth's ionosphere is composed of three main parts: the D, E, and F regions, ranging from about 50-150 miles above the Earth's surface. 

Earth's atmosphere and ionosphere (Stanford)

The ionosphere is of major importance to us because it influences radio wave propagation across distances. The ionosphere and the ground produce a “waveguide” through which radio signals can bounce back and forth, making their way around the curved Earth.  At night, without ionization by normal solar radiation, the D layer disappears, leaving the ionosphere with only the E and F layers. So radio waves from Earth echo back from these higher layers, and travel further around the Earth. That's why people on the East Coast can sometimes pick up night-time baseball game radio broadcasts from teams in the Midwest.

Radio wave propagation in the waveguide between the Earth's surface and the ionospheric D layer (Stanford)

When a solar flare occurs, the flare’s enhanced X-ray emissions (by a factor of ten or more according to the DAN program) compared to more quiet solar conditions cause an increase in the ionization of all the ionospheric layers, including the lowermost D. The ion content of D now becomes abundant enough to reflect the radio waves from a lower altitude. So during a solar flare, the waves travel a shorter distance by bouncing off D instead of E or F. Thus a so-called sudden ionospheric disturbance (SID) results from the abnormally high ionization density in the D region resulting from solar flares. The SID also causes an increase in radio-wave absorption (called radio fadeouts in the Bulletin article) which often interferes with telecommunications systems.

Space weather and its effects on our technological systems has become an increasingly important area of study since the IGY, especially as we have moved into the age of satellites and telecommunications.