Climatology of the midnight temperature maximum phenomenon at Arequipa, Peru



[1] A study of the midnight temperature maximum (MTM) climatology has been made for the low-latitude station at Arequipa, Peru (16.2°S, 71.5°W) using Fabry-Perot measurements for the period 1997–2001. Examination of the Arequipa nighttime temperature data after removal of the nocturnal cooling (as represented by the semiempirical NRLMSISE-00 model) shows a Gaussian-like time dependence with amplitudes between 20 and 200 K centered on 0400–0600 UT. A typical value of 50 to 75 K was found for data averaged over the nights from late March to early October, cloudy skies preventing measurements during summer months (November–February). These data show the MTM activity to fluctuate sporadically throughout the austral winter. Also evident are large variations of the offset between the observed temperatures and the MSIS model, with individual nightly offsets between ±200 K. Averaging these offsets over all nights for any 1 year and for all 5 years reduces the offset to a value of ∼20 K. The observed time for the occurrence of the MTM peak amplitude exhibits a seasonal variation; during winter solstice the peak typically occurs between 0500 and 0700 UT, later than during the fall and spring equinoxes, when the peak occurs between 0300 and 0500 UT. The variation of the MTM amplitude with day number shows a weak semiannual oscillation with peak values of 150–200 K near equinoxes and a small secondary maximum of 50 to 70 K near the winter solstice. Examination of the variation of the yearly-averaged MTM amplitude between solar minimum and solar maximum show a slight trend featuring a ∼20 K reduction.