Abstract
The authors study the NCEP–NCAR reanalysis temperature records and find that surface daily mean temperature cools rapidly and warms gradually at the midlatitudes (around 40°N and 40°S). This “asymmetry” is partially related to the midlatitude cyclone activity, in which cold fronts are significantly faster and steeper than warm fronts, and to intrusions of cold air. The gradual warming may be attributed also to the radiative relaxation to average atmospheric conditions after the passage of cold fronts or other intrusions of cold air. At the high latitudes there is an opposite asymmetry with rapid warming and gradual cooling; this asymmetry may be attributed to the radiative relaxation to average cold atmospheric conditions after the passage of warm fronts or intrusions of warm air.
Highlights
Among the various measures that quantify past and future climate, temperature is one of the most common and important measures
As follows from Bartos and Jánosi (2005) and Gyüre et al (2007), we find here that the daily temperature asymmetry is limited to the midlatitudes; we propose that the asymmetry is partially due to the fact that cold fronts, which usually occur at these latitudes, are sharper and induce faster transitions than warm fronts
There are several features that are worth noting. (i) The asymmetry is maximal at the midlatitudes (ϳ40°N and ϳ40°S), reflecting rapid cooling and gradual warming. (ii) At the tropics the asymmetry is ϳ0.5, indicating that on average the warming and cooling rates are almost the same. (iii) Asymmetry is more pronounced over land. (iv) The high-asymmetry patterns approximately overlap the storm track. (v) High asymmetry values tend to be found at eastern part of the continents. (vi) Opposite asymmetry is observed at the high latitudes, indicating rapid warming and gradual cooling
Summary
Among the various measures that quantify past and future climate, temperature is one of the most common and important measures. One of the basic characteristics of earth climate in the past 3 million years or so is the asymmetry of the glacial–interglacial cycles in which temperature cools gradually and warms rapidly (Imbrie et al 1984; Lisiecki and Raymo 2005; Ashkenazy and Tziperman 2004). Asymmetry is of interest because it may be a basic sign for a nonlinear underlying process (Schreiber and Schmitz 2000; Bartos and Jánosi 2005, 2006; Gyüre et al 2007) and the asymmetry of different climate records may be associated with different underlying nonlinear dynamics It was found (Bartos and Jánosi 2005, 2006; Gyüre et al 2007), based on the available land temperature records, that daily mean temperature cools rapidly and warms gradually. We propose that the asymmetry of temperature time series may be used as a measure of the nonlinearity, possibly adding another point of view to this discussion
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