Find in Library

<p>The literature presents different views on how the stratosphere influences variability in surface nitrous oxide (N<span class="inline-formula">₂</span>O) and on whether that influence is outweighed by surface emission changes driven by the El Niño–Southern Oscillation (ENSO). These questions are investigated using a chemistry–climate model with a stratospheric N<span class="inline-formula">₂</span>O tracer; surface and aircraft-based N<span class="inline-formula">₂</span>O measurements; and indices for ENSO, polar lower stratospheric temperature (PLST), and the stratospheric quasi-biennial oscillation (QBO). The model simulates well-defined seasonal cycles in tropospheric N<span class="inline-formula">₂</span>O that are caused mainly by the seasonal descent of N<span class="inline-formula">₂</span>O-poor stratospheric air in polar regions with subsequent cross-tropopause transport and mixing. Similar seasonal cycles are identified in recently available N<span class="inline-formula">₂</span>O data from aircraft. A correlation analysis between the N<span class="inline-formula">₂</span>O atmospheric growth rate (AGR) anomaly in long-term surface monitoring data and the ENSO, PLST, and QBO indices reveals hemispheric differences. In the Northern Hemisphere, the surface N<span class="inline-formula">₂</span>O AGR is negatively correlated with winter (January–March) PLST. This correlation is consistent with an influence from the Brewer–Dobson circulation, which brings N<span class="inline-formula">₂</span>O-poor air from the middle and upper stratosphere into the lower stratosphere with associated warming due to diabatic descent. In the Southern Hemisphere, the N<span class="inline-formula">₂</span>O AGR is better correlated to QBO and ENSO indices. These different hemispheric influences on the N<span class="inline-formula">₂</span>O AGR are consistent with known atmospheric dynamics and the complex interaction of the QBO with the Brewer-Dobson circulation. More airborne surveys extending to the tropopause would help elucidate the stratospheric influence on tropospheric N<span class="inline-formula">₂</span>O, allowing for better understanding of surface sources.</p>