Model Seasonal Data 

Fit a SARMAProcess model for the hourly measurements of the temperature in August.

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X data = Select[WeatherData["Champaign", "Temperature", {2012, 8}], FreeQ[#, Missing] &];

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X DateListPlot[data, Filling -> Bottom, Joined -> True]

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Find process parameters.

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X eproc = EstimatedProcess[data[[All, 2]], SARMAProcess[{}, {}, {24, {c}, {d}}, v], ProcessEstimator -> "MethodOfMoments"]

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Check if the process is weakly stationary.

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X WeakStationarity[eproc]

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Compare correlation functions.

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X ListPlot[CorrelationFunction[#, {100}] & /@ {eproc, data[[All, 2]]}, PlotStyle -> {PointSize[Large], PointSize[Medium]}, PlotRange -> All, PlotLegends -> Placed[{"Model", "Data"}, {Right, Top}], ImageSize -> 300]

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