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Model experiments

This study presents the results from 10 years of CAM4.0 control simulations and 18 forced experiments investigating the impact of idealized heating and cooling signals on precipitation patterns. Each forced experiment lasted 135 days and included different seasonal initial conditions. The findings indicate that seasonal variations in precipitation during JJAS and DJFM are influenced by the oscillations, with the JJAS season showing superior capture quality. The study highlights the effectiveness of the 45-day period oscillation in improving anomaly structures in precipitation.

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Model experiments

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  1. Model experiments • CAM4.0 was run for 10 years without any forcing at 1deg resolution - the control run (data ocean). • Each of the forced experiments were run for 135 days. • 18 forced experiments with eastward moving heating and cooling signals were run - each for 10 different initial conditions : • the 31 May of each year from the control run - 10 JJAS I.C. • the 30 Nov of each year from the control run - 10 DJFM I.C. • 2 forced experiments with northward moving forcing were run - each for 10 different initial conditions, 1 for each season’s I.C. • 2 forced experiments with stationary forcing over the equatorial Indian Ocean were run - each for 10 different initial conditions, 1 for each season’s I.C. • 6 forced experiments each with varying latitudinal extent of observed Diabatic Heating were run - each for 10 different initial conditions, 3 for each season’s I.C.

  2. The forced experiments with idealized signals have heating and cooling cells based on idealized MJO-like oscillations: • ellipses with Gaussian distribution (cell size 60deg lon, 10deg lat) • with middle heavy and bottom heavy vertical profiles • alternate heating and cooling signals • maxima is 1.5K/day for both the profiles reducing to almost zero at the top and bottom of the atmosphere • They cover the equatorial Indo-Pacific region Vertical Profile: bottom heavy, middle heavy,

  3. Forced Signals (Idealized) Multichannel singular spectrum (MSSA) has been used to identify the temporal variability and to determine the coherent intraseasonal space-time patterns for different variables. The 45 day period oscillation is studied, which also captures the MJO.

  4. JJAS: Precipitation (mm/day) Observation Control_runf_rs3(45dp)

  5. DJFM: Precipitation (mm/day) Observation Control_run f_rw3(45dp)

  6. The JJAS season is better captured than the DJFM season by CAM4.0 as seen in the control run. • The best results are seen for the 45 day period (dp) oscillation with middle heavy vertical profile, for both the JJAS and DJFM seasons. • For JJAS, the 45dp forcing signal improves the anomaly band tilts. • For DJFM, the 45dp forcing signal improves the eastward propagation of the anomalies and reduces the northern hemispheric anomalies. • It is interesting to note that an eastward propagating forcing improves the latitudinal structure of the anomalies.

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