The role of inertial instability in cross-hemispheric coupling

View More View Less
  • 1 NASA Goddard Space Flight Center, Greenbelt, MD
  • 2 GATS Inc., Boulder, CO
  • 3 Northwest Research Associates, Inc., Redmond, WA
  • 4 U. S. Naval Research Laboratory, Washington, D. C.
© Get Permissions
Restricted access

Abstract

Recent studies suggest linkages between anomalously warm temperatures in the winter stratosphere, and the high-latitude summer mesopause. The summer temperature anomaly is manifested in the decline of polar mesospheric clouds. The two-day wave is a strong-amplitude and transient summer feature that interacts with the background state so as to warm the high-latitude summer mesopause. This wave has been linked to a low-latitude phenomenon called inertial instability, that is organized by breaking planetary waves in the winter stratosphere. Hence, inertial instability has been identified as a possible nexus between the disturbed winter stratosphere, and summer mesopause warming. We investigate a sustained occurrence of inertial instability during July 19-August 8, 2014. During this period, stratospheric winter temperatures warmed by about 10 K, while a steep decline in polar mesospheric clouds was reported between July 26–August 6. We present, for the first time, wave driving associated with observed inertial instability. The effect of inertial instability is to export eastward momentum from the winter hemisphere across the equator into the summer hemisphere. Using a primitive equation model, we demonstrate that the wave stresses destabilize the stratopause summer easterly jet. The reconfigured wind profile excites the wavenumber 4 component of the two-day wave, leading to enhanced warming of the summer mesopause. This work supports previous numerical investigations that identified planetary wave-driven inertial instability as a source of the two-day wave.

Corresponding author: R. S. Lieberman, ruth.s.lieberman@nasa.gov

Abstract

Recent studies suggest linkages between anomalously warm temperatures in the winter stratosphere, and the high-latitude summer mesopause. The summer temperature anomaly is manifested in the decline of polar mesospheric clouds. The two-day wave is a strong-amplitude and transient summer feature that interacts with the background state so as to warm the high-latitude summer mesopause. This wave has been linked to a low-latitude phenomenon called inertial instability, that is organized by breaking planetary waves in the winter stratosphere. Hence, inertial instability has been identified as a possible nexus between the disturbed winter stratosphere, and summer mesopause warming. We investigate a sustained occurrence of inertial instability during July 19-August 8, 2014. During this period, stratospheric winter temperatures warmed by about 10 K, while a steep decline in polar mesospheric clouds was reported between July 26–August 6. We present, for the first time, wave driving associated with observed inertial instability. The effect of inertial instability is to export eastward momentum from the winter hemisphere across the equator into the summer hemisphere. Using a primitive equation model, we demonstrate that the wave stresses destabilize the stratopause summer easterly jet. The reconfigured wind profile excites the wavenumber 4 component of the two-day wave, leading to enhanced warming of the summer mesopause. This work supports previous numerical investigations that identified planetary wave-driven inertial instability as a source of the two-day wave.

Corresponding author: R. S. Lieberman, ruth.s.lieberman@nasa.gov
Save