What causes the irregular cycle of the atmospheric tape recorder signal in HCN?

Abstract

Variations in the mixing ratio of long‐lived trace gases entering the stratosphere in the tropics are carried upward with the rising air with the signal being observable throughout the tropical lower stratosphere. This phenomenon, referred to as “atmospheric tape recorder” has previously been observed for water vapor, CO2, and CO which exhibit an annual cycle. Recently, based on Microwave Limb Sounder (MLS) and the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE‐FTS) satellite measurements, the tape recorder signal has been observed for hydrogen cyanide (HCN) but with an approximately two‐year period. Here we report on a model simulation of the HCN tape recorder for the time period 2002–2008 using the Chemical Lagrangian Model of the Stratosphere (CLaMS). The model can reproduce the observed pattern of the HCN tape recorder signal if time‐resolved emissions from fires in Indonesia are used as lower boundary condition. This finding indicates that inter‐annual variations in biomass burning in Indonesia, which are strongly influenced by El Niño events, control the HCN tape recorder signal. A longer time series of tropical HCN data will probably exhibit an irregular cycle rather than a regular biannual cycle.

Seasonal and interannual variations in HCN amounts in the upper troposphere and lower stratosphere observed by MIPAS

“…In the whole MIPAS data set, annual or semi-annual cycles prevail in the tropical upper troposphere due to overlapping signatures from the Northern and Southern Hemisphere, while variations in the lower stratosphere exhibit periodicities of 2 and 4 years. These periodicities, however, do not have a direct meteorological reason but are rather introduced by the interannual variations in biomass burning as already outlined by Pommrich et al (2010). The broad positive anomalies starting at the tropical tropopause in 2003, 2007 and 2011 are due to contributions from strong southern hemispheric and Indonesian biomass burning in boreal autumn and from northern tropical Africa and the AMA in subsequent boreal spring and summer.…”

“…On the other hand, interannual variations in the meteorology were shown to have little influence on the HCN amounts in the upper troposphere and lower stratosphere (UTLS) region. Pommrich et al (2010) were able to reproduce the observed 2-year tape recorder signal with the Chemical Lagrangian Model of the Stratosphere (CLaMS) by use of temporally resolved biomass burning emissions from Indonesia. However, they expected an irregular cycle for a longer time series, because Indonesian biomass burning is strongly influenced by El Niño events.…”

Quantifying pollution transport from the Asian monsoon anticyclone into the lower stratosphere

“…Hence, a contribution from the SH to stratospheric HCN cannot be ruled out. Furthermore, the irregular tape-recorder signal in the deseasonalized anomaly of tropical HCN during (Pumphrey et al, 2007 has been linked to irregularly occurring biomass burning in Indonesia (Pommrich et al, 2010). Compared to these studies, the focus here is on the annually repeating seasonal signal discussed by Randel et al (2010).…”

Methyl chloride from the Aura Microwave Limb Sounder: First global climatology and assessment of variability in the upper troposphere and stratosphere

“…Pumphrey et al [2008] demonstrated that a tape recorder signal is detectable in MLS measurements of hydrogen cyanide (HCN), despite their poor vertical resolution (6-8 km over the altitude range 32-20 km). The irregular periodicity in the HCN tape recorder has been shown to be controlled mainly by interannual variations in biomass burning in Indonesia (strongly influenced by El Niño events, as discussed above) [Pumphrey et al, 2008;Li et al, 2009;Pommrich et al, 2010;Randel et al, 2010]. Given that CH 3 Cl has vertical resolution comparable to that of CO and better than that of HCN (species in which a tape recorder has previously been discerned), it should also exhibit such a signature, although it must be borne in mind that the detailed vertical structure of the propagating features is inevitably attenuated by the relatively coarse MLS vertical resolution.…”