The radar tropopause above Svalbard 2008–2012: Characteristics at various timescales

Abstract

[1] Determinations of the tropopause altitude over Adventdalen, Svalbard (78 N, 16 E) have been assembled for the period 2008-2012. These reveal characteristics at various timescales: interannual, seasonal, and stochastic. First, it is established that the inclusion of considerably more data does not alter earlier findings of good temporal agreement with radiosonde measurements, that the radar tropopause is located at a fairly constant altitude above the meteorological tropopause, and that the seasonal variation lags the surface temperature variation by approximately 1 month, indicating a degree of top-down control from the stratosphere. Over the longest timescale available, i.e., 5 years, we find an increase in tropopause altitude and identify this with increasing solar flux during the growth phase of solar cycle 24, and contrary to the seasonal variation, there is evidence that this is controlled by troposphere warming. At stochastic timescales, the scaling characteristics of the signal are examined, and in an exploratory investigation, the Hurst exponent is found to be~0.82, which is in excellent agreement with independent findings for high latitude surface temperature data and therefore supportive of a complexity matching approach to identification of causal relationships between atmospheric metrics.

Change in turbopause altitude at 52 and 70° N

“…If such effects were capable of, for example, triggering the springtime breakdown of the polar vortex, associated horizontal transport of stratospheric ozone would contribute to determination of the tropopause altitude (e.g. Hall, 2013) and, again, gravity wave propagation. Overall change in the stratosphere is proposed as the origin of the observed strengthening of the Brewer-Dobson circulation during the last 35 years at least (Fu et al, 2015).…”

Change in turbopause altitude at 52 and 70° N

“…If such effects were capable of, for example, triggering the springtime breakdown of the polar vortex, associated horizontal transport of stratospheric ozone would contribute to determination of the tropopause altitude (e.g. Hall, 2013) and, again, gravity wave propagation. Overall change in the stratosphere is proposed as the origin of the observed strengthening of the Brewer-Dobson circulation during the last 35 years at least (Fu et al, 2015).…”

“…The generation of turbulence and its height distribution vary with season and similarly affect the turbopause altitude (e.g. Hall et al, 1997). Turbulence is somewhat distributed through the high-latitude win-2300 C. M. Hall et al: Change in turbopause altitude at 52 and 70 • N ter mesosphere, whereas in summer the gravity waves "save their energy" more until reaching the "steep beach" (a visualisation attributable to M. E. McIntyre, personal communication, 1988) of the summer mesopause near 85 km.…”

The radar tropopause at 78°N, 16°E: Characteristics of diurnal variation

“…Somewhat exhaustive comparisons have been made between the radar results which will be presented here and the tropopause determinations from radiosonde soundings nearby (Ny‐Ålesund, 79°N, 12°E), showing a high degree of agreement in temporal behavior and that the altitude difference between the two determinations is almost invariant—1.8 ± 0.3 km—with a slight seasonal variation [ Hall et al . ; Hall , ] contained within the standard deviation. It has been demonstrated that it is viable to convert between radar and cold‐point tropopause altitudes at least for the SOUSY radar and radiosonde measurements currently available on Svalbard.…”

“…At both intra‐annual and interannual scales, the agreement in temporal variation between the climatology and the 78°N, 16°E observations is good. Although not a topic of this study, there is a suggestion of convergence of the observations on the climatology, indicative of a systematic increase in tropopause height over the 5 years of measurements [ Hall , ]. Subsequently in this study, underlying 1 h resolution values will be used, and the term “tropopause” will be used to refer to the radar (height of peak echo) tropopause hereafter.…”