The Walker circulation is the result of a difference in surface pressure and temperature over the western and eastern tropical Pacific Ocean. A pressure gradient from east to west and causes surface air to from high pressure in the eastern Pacific to low pressure in the western Pacific. Higher up in the atmosphere, west-to-east winds complete the circulation.
Surface temperatures vary more than air temperatures during the day, but they both are fairly similar at night. The dip and spike in surface temperatures over the pond show how water maintains a fairly constant temperature day and night, due to its high heat capacity. The temperatures displayed do not represent absolute temperature values.