With reference to Ocean Mean Temperature (OMT), which of the following statements is/are correct? 1) OMT is measured up to a depth of 26°C isotherm which is 129 meters in the south-western Indian Ocean during January- March. 2) OMT collected during January – March be used in assessing whether the amount of rainfall in monsoon will be less or more than a certain long-term mean. Select the correct answer using the code given below:

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CollectorBabu · Accepted Answer

Correct Answer: 2 only. Ocean Mean Temperature: Ocean Temperature is a measure of the energy due to the motion of molecules in the ocean. Sea surface temperature (SST) is routinely used for predicting whether the total amount of rainfall that India receives during the monsoon season will be less or more than the long-term mean of 887.5 mm. Now, scientists from Pune’s Indian Institute of Tropical Meteorology (IITM) find that ocean mean temperature (OMT) that has better ability to predict this than the sea surface temperature. Compared with SST which has 60% success rate of predicting the Indian summer monsoon, OMT has 80% success rate. This is because OMT is analysed by measuring the ocean thermal energy during the period from January to March. Hence, Statement 2 is correct. The SST is restricted to a few millimetres of the top ocean layer and is largely influenced by strong winds, evaporation, or thick clouds. In contrast, OMT, which is measured up to a depth of 26 degree C isotherm, is more stable and consistent, and the spatial spread is also less. The 26 degree C isotherm is seen at depths varying from 50–100 metres. During January–March, the mean 26 degree C isotherm depth in the Southwestern Indian Ocean is 59 metres. Statement 1 is NOT correct. “Using OMT data collected during January-March 2018, we were able to predict with 80% probability that this year’s monsoon will be below average during June–September,”. OMT showed better success in predicting above or below-average rainfall years compared with SST. OMT predicted successfully 13 out of 16 below average rainfall years and seven out of nine above average rainfall years during the period 1993-2017. Hence the answer is Option B.

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