I want extend the scope of Oxyplot plotmodel for event handlers

I want that my plotview replies to more than one event handler, so I declared the plotmodel outside the event handler bloc, and the result was that it is out of scope of the event handler.

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Windows.Forms;

// for plotting///////
using OxyPlot;
using OxyPlot.Series;

namespace test
{

public partial class MainForm : Form

{
public MainForm()
{
InitializeComponent();
var myModel = new PlotModel { Title = "Example 1" };
plot1.Invalidate(true);
myModel.InvalidatePlot(true);
}


void HScrollBar1Scroll(object sender, ScrollEventArgs e)

{

int hScrollBar1_Value = this.hScrollBar1.Value;
Func<double,double> func1 = (x) => Math.Cos(x)/(1+hScrollBar1_Value);
myModel.Series.Add(new FunctionSeries(func1, 0, 5, 0.1, "cos(x)"));
plot1.Model = myModel;
}
}
}

this way the vent handler has no effect and an error is generated. Is there any other way to make the event handlers access the plotmodel?