Bjerknes Feedback Mechanism Failure

The Bjerknes feedback describes a process linking sea surface temperature (SST) anomalies and wind anomalies in the tropical Pacific. It typically involves warmer SSTs in the western Pacific compared to the central Pacific.

• Mechanism: Warmer western SSTs enhance convection, leading to increased rainfall and atmospheric pressure changes. This typically strengthens the easterly trade winds.
• Feedback Loop: Stronger easterly winds push more warm surface water westward, reinforcing the SST gradient (warmer west, cooler central/east).

Role of Earth's Rotation

The existence and strength of large-scale atmospheric circulation patterns, such as the trade winds, are fundamentally dependent on the rotation of the Earth (Coriolis effect).

• The Coriolis effect deflects moving air masses, creating the characteristic zonal (east-west) flow of the trade winds in the tropics.
• These trade winds are crucial for maintaining the SST gradient central to the Bjerknes feedback.

Why Rotation is Essential

If there were no rotation of the Earth:

• The Coriolis effect would be absent.
• The characteristic large-scale trade wind patterns would not be established or sustained in the same manner.
• Without these winds, the mechanism that maintains the SST difference between the western and central tropical Pacific would fail, breaking the Bjerknes feedback loop.

Analysis of Other Options

• Uniform salinity: While salinity influences water density, temperature gradients are the primary driver for the large-scale atmospheric and oceanic circulation relevant to this feedback. Uniform salinity alone wouldn't stop the feedback.
• Cooler tropics (3°C): A temperature change would alter the absolute values but not necessarily break the relative gradient and feedback mechanism itself, unless it fundamentally changed the atmospheric dynamics.
• Absence of typhoons: Typhoons are a symptom of warm SSTs and instability, not the core driver of the large-scale wind-SST interaction that defines the Bjerknes feedback. Their absence wouldn't necessarily halt the feedback.

Therefore, the Bjerknes feedback mechanism, as described by the SST gradient between the western and central tropical Pacific maintained by wind anomalies, critically depends on the rotation of the Earth.