Recent observations by Hinode during the solar activity minimum
revealed that quiet regions and coronal holes are not really quiet.
X-ray bright points are found all over the Sun,
and they occasionally undergo impulsive brightenings or microflares.
Improved resolution of Hinode EIS and XRT allows us to follow
a temporal evolution of the microflares.
It is interesting to note that microflares in bright points and
large flares in active regions share some common characteristics.
shows lightcurves of different temperature emission lines
as a microflare occurred in a quiet region.
Hot emission lines (greater than 1 MK) exhibit primary peaks
coincident with an X-ray peak.
A noticeable increase in Fe XV emission, which is normally
weak in quiet regions, indicates heating in the microflare.
An electron density derived from the ratio of Fe XII emission lines
indicates a density increase at the primary peak,
which suggests chromospheric evaporation.
Twelve minutes later, cool emission lines showed
a delayed peak.
Assuming a tiny loop with a diameter of the bright point, the estimated
cooling time of the coronal loop agrees with the delayed cool emission.
This kind of delayed cool emission is frequently observed in flare loops
in active region.
The properties of microflares nicely fit that of flares in active regions,
though their scales are quite different.
The lightcurves of microflares in coronal holes and in quiet regions
are basically the same, but there exists a difference in their surroundings.
displays running difference of X-ray images in the course of
two distinct microflares in a coronal hole (left panel) and in
a quiet region (right panel).
A microflare in the coronal hole produces a jet above the bright point,
indicating an ejection of hot material along open magnetic field lines.
In contrast, the microflare exhibits coronal dimming in the quiet region,
which is interpreted as rearrangement of closed magnetic fields
triggered by the microflare, analogous to a large scale coronal dimming
in active regions.
The behavior of the surroundings reflects different magnetic field
configurations in coronal holes and quiet regions.