The mean kinetic energy of the atoms of an ideal gas is directly proportional to the absolute temperature, according to the kinetic theory of gases:
\[
E \propto T
\]
where \( E \) is the mean kinetic energy and \( T \) is the absolute temperature in Kelvin.
The temperature in Kelvin can be calculated as:
\[
T_1 = 27^\circ C + 273 = 300 \, \text{K}, \quad T_2 = 327^\circ C + 273 = 600 \, \text{K}
\]
Now, the ratio of the mean kinetic energies at temperatures \( T_1 \) and \( T_2 \) is:
\[
\frac{E_2}{E_1} = \frac{T_2}{T_1} = \frac{600}{300} = 2
\]
Therefore, the new mean kinetic energy \( E_2 \) is:
\[
E_2 = 2E_1
\]
Thus, the correct option is:
\[
2E_1
\]