Detection of multi-decadal time-scale variability in temperature anomalies (deg. Cent.) over land+marine regions for the Southern Hemisphere for the period 1867 to 1996 i.e. 130 years

Detection of multi-decadal time-scale variability in temperature anomalies (?C) over land + ocean regions for the Southern Hemisphere for the period 1867 to 1996 i.e. 130 years

C. P. Kulkarni

Indian Institute of Tropical Meteorology, Pashan Road, Pune - 411 008, India e-mail : cpk@tropmet.ernet.in

ABSTRACT

The study of Earth’s climate and its variability is enormously complex. This complexity arises from our inadequate knowledge of the various components of the climate systems viz.oceans, atmosphere, cryosphere and land surface. Each of these components undergoes complex interactions with other over time. In order to monitor the effect of increasing greenhouse gases in the Earth’s atmosphere and climate trends, important parameters like ocean and land surface temperatures are essential. To study the multi-decadal variability in the southern hemisphere temperature anomalies, the long-term dataset for the monthly average temperature anomalies (?C) over land + ocean regions for the period 1867 to 1996 i.e. 130 years has been used from the published work of Dr. P.D. Jones.

A statistical technique i.e. harmonic analysis has been applied for the above dataset to detect the predominant waves, their periodicities, percentage variance to the total variance, amplitudes and phases. After doing wave analysis, it is noticed that wave number one is predominant with 47% variance, 0.20 amplitude and 290 degree phase. The said wave number one is plotted and shown in the figure. From the figure, it is observed that the entire period can be split up to into two climate conditions. The first half being below mean (cold climate) during the period 1867 to 1939 and the second half being above mean (warm climate) during the period 1940 to 1996.

It would be a good exercise to examine the position of year of maxima and minima of wave number one in relation to severmost flood and drought year appeared in the southern hemispheric continental regions vis. South America, South Africa, Australia and Southeast Asia. This is because, similar type of analysis was carried out for the northern hemisphere temperature anomalies for the same period and it was found very interesting to note that the minima of wave number one was coinciding with severmost drought year in India (-20%) and maxima was coinciding with height rainfall year in India (+19.4%) during the century.