Seasonal temperature waves in the ground, nonperiodic case

Seasonal fluctuations in soil temperature at a depth of several meters are considered. It is assumed that the earth surface changes strictly periodically. Then, according to Fourier law, will also change periodically with smaller amplitude and time lag. What happens if we let on deviate from strict periodicity some point time? How nature depth? Two types deviations periodic law considered: 1) A sharp cold snap. For 30 days, -30оC 2) Warm winter. zero during winter months. Graphs different depths both cases plotted. Conclusions drawn about duration period noticeable magnitude deviation normal value.