25 research outputs found
Is it feasible to estimate radiosonde biases from interlaced measurements?
Upper-air measurements of essential climate variables (ECVs), such as temperature, are crucial for climate monitoring and climate change detection. Because of the internal variability of the climate system, many decades of measurements are typically required to robustly detect any trend in the climate data record. It is imperative for the records to be temporally homogeneous over many decades to confidently estimate any trend. Historically, records of upper-air measurements were primarily made for short-term weather forecasts and as such are seldom suitable for studying long-term climate change as they lack the required continuity and homogeneity. Recognizing this, the Global Climate Observing System (GCOS) Reference Upper-Air Network (GRUAN) has been established to provide reference-quality measurements of climate variables, such as temperature, pressure, and humidity, together with well-characterized and traceable estimates of the measurement uncertainty. To ensure that GRUAN data products are suitable to detect climate change, a scientifically robust instrument replacement strategy must always be adopted whenever there is a change in instrumentation. By fully characterizing any systematic differences between the old and new measurement system a temporally homogeneous data series can be created. One strategy is to operate both the old and new instruments in tandem for some overlap period to characterize any inter-instrument biases. However, this strategy can be prohibitively expensive at measurement sites operated by national weather services or research institutes. An alternative strategy that has been proposed is to alternate between the old and new instruments, so-called interlacing, and then statistically derive the systematic biases between the two instruments. Here we investigate the feasibility of such an approach specifically for radiosondes, i.e. flying the old and new instruments on alternating days. Synthetic data sets are used to explore the applicability of this statistical approach to radiosonde change management
Recommended from our members
Evaluating stratospheric ozone and water vapour changes in CMIP6 models from 1850 to 2100
Stratospheric ozone and water vapour are key components of the Earth system, and past and future changes to both have important impacts on global and regional climate. Here, we evaluate long-term changes in these species from the pre-industrial period (1850) to the end of the 21st century in Coupled Model Intercomparison Project phase 6 (CMIP6) models under a range of future emissions scenarios. There is good agreement between the CMIP multi-model mean and observations for total column ozone (TCO), although there is substantial variation between the individual CMIP6 models. For the CMIP6 multi-model mean, global mean TCO has increased from ∼300 DU in 1850 to ∼ 305 DU in 1960, before rapidly declining in the 1970s and 1980s following the use and emission of halogenated ozone-depleting substances (ODSs). TCO is projected to return to 1960s values by the middle of the 21st century under the SSP2-4.5, SSP3-7.0, SSP4-3.4, SSP4-6.0, and SSP5-8.5 scenarios, and under the SSP3-7.0 and SSP5-8.5 scenarios TCO values are projected to be ∼ 10 DU higher than the 1960s values by 2100. However, under the SSP1-1.9 and SSP1-1.6 scenarios, TCO is not projected to return to the 1960s values despite reductions in halogenated ODSs due to decreases in tropospheric ozone mixing ratios. This global pattern is similar to regional patterns, except in the tropics where TCO under most scenarios is not projected to return to 1960s values, either through reductions in tropospheric ozone under SSP1-1.9 and SSP1-2.6, or through reductions in lower stratospheric ozone resulting from an acceleration of the Brewer-Dobson circulation under other Shared Socioeconomic Pathways (SSPs). In contrast to TCO, there is poorer agreement between the CMIP6 multi-model mean and observed lower stratospheric water vapour mixing ratios, with the CMIP6 multi-model mean underestimating observed water vapour mixing ratios by ∼ 0.5 ppmv at 70 hPa. CMIP6 multi-model mean stratospheric water vapour mixing ratios in the tropical lower stratosphere have increased by ∼ 0.5 ppmv from the pre-industrial to the present-day period and are projected to increase further by the end of the 21st century. The largest increases (∼ 2 ppmv) are simulated under the future scenarios with the highest assumed forcing pathway (e.g. SSP5-8.5). Tropical lower stratospheric water vapour, and to a lesser extent TCO, shows large variations following explosive volcanic eruptions. © Author(s) 2021
Evaluating stratospheric ozone and water vapour changes in CMIP6 models from 1850 to 2100
Stratospheric ozone and water vapour are key components of the Earth system, and past and future changes to both have important impacts on global and regional climate. Here, we evaluate long-term changes in these species from the pre-industrial period (1850) to the end of the 21st century in Coupled Model Intercomparison Project phase 6 (CMIP6) models under a range of future emissions scenarios. There is good agreement between the CMIP multi-model mean and observations for total column ozone (TCO), although there is substantial variation between the individual CMIP6 models. For the CMIP6 multi-model mean, global mean TCO has increased from ∼300 DU in 1850 to ∼ 305 DU in 1960, before rapidly declining in the 1970s and 1980s following the use and emission of halogenated ozone-depleting substances (ODSs). TCO is projected to return to 1960s values by the middle of the 21st century under the SSP2-4.5, SSP3-7.0, SSP4-3.4, SSP4-6.0, and SSP5-8.5 scenarios, and under the SSP3-7.0 and SSP5-8.5 scenarios TCO values are projected to be ∼ 10 DU higher than the 1960s values by 2100. However, under the SSP1-1.9 and SSP1-1.6 scenarios, TCO is not projected to return to the 1960s values despite reductions in halogenated ODSs due to decreases in tropospheric ozone mixing ratios. This global pattern is similar to regional patterns, except in the tropics where TCO under most scenarios is not projected to return to 1960s values, either through reductions in tropospheric ozone under SSP1-1.9 and SSP1-2.6, or through reductions in lower stratospheric ozone resulting from an acceleration of the Brewer-Dobson circulation under other Shared Socioeconomic Pathways (SSPs). In contrast to TCO, there is poorer agreement between the CMIP6 multi-model mean and observed lower stratospheric water vapour mixing ratios, with the CMIP6 multi-model mean underestimating observed water vapour mixing ratios by ∼ 0.5 ppmv at 70 hPa. CMIP6 multi-model mean stratospheric water vapour mixing ratios in the tropical lower stratosphere have increased by ∼ 0.5 ppmv from the pre-industrial to the present-day period and are projected to increase further by the end of the 21st century. The largest increases (∼ 2 ppmv) are simulated under the future scenarios with the highest assumed forcing pathway (e.g. SSP5-8.5). Tropical lower stratospheric water vapour, and to a lesser extent TCO, shows large variations following explosive volcanic eruptions
The 1985 Southern Hemisphere mid-latitude total column ozone anomaly
One of the most significant events in the evolution
of the ozone layer over southern mid-latitudes since the
late 1970s was the large decrease observed in 1985. This
event remains unexplained and a detailed investigation of
the mechanisms responsible for the event has not previously
been undertaken. In this study, the 1985 Southern Hemisphere
mid-latitude total column ozone anomaly is analyzed
in detail based on observed daily total column ozone fields,
stratospheric dynamical fields, and calculated diagnostics of
stratospheric mixing. The 1985 anomaly appears to result
from a combination of (i) an anomaly in the meridional circulation
resulting from the westerly phase of the equatorial
quasi-biennial oscillation (QBO), (ii) weaker transport
of ozone from its tropical mid-stratosphere source across the
sub-tropical barrier to mid-latitudes related to the particular
phasing of the QBO with respect to the annual cycle,
and (iii) a solar cycle induced reduction in ozone. Similar
QBO and solar cycle influences prevailed in 1997 and 2006
when again total column ozone was found to be suppressed
over southern mid-latitudes. The results based on observations
are compared and contrasted with analyses of ozone
and dynamical fields from the ECHAM4.L39(DLR)/CHEM
coupled chemistry-climate model (hereafter referred to as
E39C). Equatorial winds in the E39C model are nudged towards
observed winds between 10o S and 10o N and the ability
of this model to produce an ozone anomaly in 1985, similar
to that observed, confirms the role of the QBO in effecting
the anomaly
Effects of ozone cooling in the tropical lower stratosphere and upper troposphere
In this paper, we examine the tropical lower stratosphere and upper troposphere and elucidate the key role of ozone changes in driving temperature trends in this region. We use a radiative fixed dynamical heating model to show that the effects of tropical ozone decreases at 70 hPa and lower pressures can lead to significant cooling not only at stratospheric levels, but also in the ''sub-stratosphere/ upper tropospheric'' region around 150-70 hPa. The impact of stratospheric ozone depletion on upper tropospheric temperatures stems from reduced longwave emission from above. The results provide a possible explanation for the long-standing discrepancy between modeled and measured temperature trends in the uppermost tropical troposphere and can explain the latitudinal near-homogeneity of recent stratospheric temperature trends
Simple measures of ozone depletion in the polar stratosphere
We investigate the extent to which quantities that
are based on total column ozone are applicable as measures
of ozone loss in the polar vortices. Such quantities have been
used frequently in ozone assessments by the World Meteorological
Organization (WMO) and also to assess the performance
of chemistry-climate models. The most commonly
considered quantities are March and October mean column
ozone poleward of geometric latitude 63° and the spring minimum
of daily total ozone minima poleward of a given latitude.
Particularly in the Arctic, the former measure is affected
by vortex variability and vortex break-up in spring.
The minimum of daily total ozone minima poleward of a\ud
particular latitude is debatable, insofar as it relies on one
single measurement or model grid point. We find that, for
Arctic conditions, this minimum value often occurs in air
outside the polar vortex, both in the observations and in a
chemistry-climate model. Neither of the two measures shows
a good correlation with chemical ozone loss in the vortex deduced
from observations. We recommend that the minimum
of daily minima should no longer be used when comparing
polar ozone loss in observations and models. As an alternative
to the March and October mean column polar ozone
we suggest considering the minimum of daily average total
ozone poleward of 63° equivalent latitude in spring (except
for winters with an early vortex break-up). Such a definition
both obviates relying on one single data point and reduces the
impact of year-to-year variability in the Arctic vortex breakup
on ozone loss measures. Further, this measure shows a
reasonable correlation (r= − 0.75) with observed chemical
ozone loss. Nonetheless, simple measures of polar ozone loss
must be used with caution; if possible, it is preferable to use
more sophisticated measures that include additional information
to disentangle the impact of transport and chemistry on
ozone