On the structure of temperature pulsations near the surface under convective conditions

Abstract

Measurements of temperature pulsations under conditions of summer hot weather in the near-surface air layer in a deserted area were carried out using wire sensors distributed spatially and in height with a recording frequency of 1000 Hz. For the power spectra, slopes with values from “–1” to “–1.35” (scale: 0.2–2 m) are noted for frequencies below the “–5/3” inertial interval region. At frequencies above the inertial interval (scales: 0.01-0.1 m), slopes range from “–4.2” to “–5.8”. In some episodes at frequencies less than 0.1–0.3 Hz, slopes from “–0.2” to “–0.85” are observed. Based on the equations of motion in the Boussinesq approximation, we obtained estimates for the observed slopes of the spectra: “–1”, “–4/3”, and “–7/3”, characteristic of a thermally stratified medium. Using a qualitative (visual) method at different signal averaging times (1, 10, 200 s), the occurrence of thermoconvective structures of “ramps” with a temporal length of 0.3–1 s was revealed, which constitute ramps with a length of 1–10 s at larger averaging.