In Newman and Nash (2005, hereafter NN2005), the evolution of the unusual Southern Hemisphere (SH) 2002 stratospheric winter was discussed. This SH winter had a very large planetary wave-2 event in late September that resulted in an SH major stratospheric sudden warming. In particular, we stated that “This large wave event resulted in the first ever observed major stratospheric warming in the SH and split the Antarctic ozone hole.”

Sehra (2014) has asked for an explanation as to why Sehra (1975, hereafter S1975) was not referenced in NN2005. Specifically, S1975 was not cited because a major stratospheric sudden warming is not evident in those results or in the discussion. S1975 documented temperature fluctuations over Molodezhnaya station (68°S, 46°E) in the 30–80-km altitude range using 60 rocketsondes during 1972 (16 observations of winds using falling chaff, 55–90-km altitude range). The S1975 observations provide an early documentation of in situ upper-stratospheric and mesospheric temperatures and winds.

For our NN2005 paper, there are two issues with respect to S1975:

1. Did a major stratospheric sudden warming occur in 1972?

2. Are the results of S1975 germane to NN2005?

Our assertion of the 2002 major stratospheric sudden warming is based upon the World Meteorological Organization (WMO)’s Commission for Atmospheric Sciences definition (McInturff 1978):

1. If at 10 hPa or below the latitudinal mean temperature increases poleward from 60°S, and

2. An associated circulation reversal is observed (i.e., mean westerly winds poleward of 60°S are succeeded by mean easterlies in the same area).

As was shown in NN2005, the SH Antarctic temperatures at 10 hPa (~30 km) rapidly warmed (see NN2005, their Fig. 1), and as shown in NN2005 and Allen et al. (2003), the 10-hPa, 60°S zonal-mean zonal wind reversed from westerlies to easterlies in late September 2002. Hence, the major stratospheric warming conditions 1 and 2 are met in 2002.

While NN2005 and Allen et al. (2003) only considered analyses from 1979 to 2002 (the modern satellite era), Roscoe et al. (2005) examined radiosonde observations from the 1957–2002 period and found no evidence for a rapid warming comparable to 2002 at the 100- or 50-hPa level. Naujokat and Roscoe (2005) further examined historic observations to determine if dramatic temperature warmings comparable to 2002 had occurred in the pre–International Geophysical Year (IGY) period and concluded that 1972 was not a unique year in the climatological record.

Barnett (1975) showed evidence of an SH stratospheric sudden warming that occurred in July 1974 from Nimbus-4 satellite observations and a weaker warming in July 1972. However, as Schoeberl (1978) pointed out, neither of these Nimbus-4 observed events was a major stratospheric sudden warming. Hence, the satellite data from the 1972 (and other years from the 1970s) records do not show evidence of SH major stratospheric sudden warmings.

The British Antarctic Survey’s Halley radiosonde temperature record at 30 hPa shows no evidence of a 1972 major stratospheric sudden warming (Roscoe et al. 2005). The 1972 Halley observations (Fig. 1, red line) generally follow the climatology (gray shading and white line) with a rather small warming that develops in late July. In contrast, the late September 2002 major stratospheric sudden warming (blue line) has a sharp rise of more than 50 K. Halley station is located in the core of the polar vortex and therefore provides an ideal location for observing warmings and the Antarctic ozone hole.

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Halley station 30-hPa ozonesonde temperatures for 1972 (red line) and 2002 (blue line). The thin black lines, the gray areas, and the white line show the daily distributions of the 46-yr Halley data record (1957–2002). Data have been smoothed with a running 7-day boxcar filter.

Citation: Journal of the Atmospheric Sciences 71, 12; 10.1175/JAS-D-14-0227.1

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The S1975 Molodezhnaya rocketsonde temperature observations show temperature swings in the upper stratosphere and mesosphere. However, it is unclear if these temperature fluctuations reflect temperature changes over the entire Antarctic region, as would happen in a major warming, or whether they represent transient Rossby wave propagation. Figure 2 displays S1975 1972 Molodezhnaya 30-km rocketsonde observations (from Fig. 2 of S1975). There are 60 observations (approximately once per week) for characterizing the SH temperature evolution over the year—modest resolution for analyzing a major stratospheric sudden warming. For comparison, we have added the 1972 National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) Reanalysis-1 (REAN) (Kalnay et al. 1996) observations along with an REAN climatology. The REAN observations are largely based upon radiosondes for late winter and spring of 1972. The REAN data show large temperature swings over the course of the winter, as would be expected from typical Rossby wave events. Time–longitude plots of the REAN data at 30 hPa (not shown) indicate that these temperature swings are largely the result of transient eastward-propagating Rossby waves. A single station sampling once per week cannot be used to diagnose these Rossby wave effects. In particular, the rocketsondes fail to show the very large temperature fluctuations associated with a major stratospheric sudden warming. Reanalysis data from these early years have problems (e.g., Santer et al. 1999; Marshall 2002; Bromwich and Fogt 2004; Yu et al. 2010) but they also have sufficient spatial and temporal resolution to resolve major stratospheric sudden warmings.

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Molodezhnaya S1975 30-km rocketsonde temperatures for 1972 (thick black line) and REAN 10-hPa temperatures for 1972 (red line) and 2002 (blue line) interpolated to the position of Molodezhnaya. The gray areas and white line show the daily distributions of the 56-yr REAN data record. Data have been smoothed with a running 7-day boxcar filter.

Citation: Journal of the Atmospheric Sciences 71, 12; 10.1175/JAS-D-14-0227.1

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The rocketsonde data in Fig. 2 also show about a 10-K RMS difference with the REAN data. The source of this problem is not known, but Finger et al. (1975) report 1–2-K differences between rocketsondes at 30 km. S1975 provides no information on the quality of the rocketsonde observations. The temperature variations in Fig. 2 are unremarkable and modest in comparison to the variations observed during the 2002 winter with the major stratospheric warming.

The REAN data do not show evidence of a 1972 major warming. Figure 3a shows the 1972 zonal-mean 60°–90°S temperature gradient, and at 10 hPa there is no temperature gradient reversal, except for the reversal associated with the winter-to-summer transition of the final warming (red arrows). However, there are temperature variations that modify the thermal gradient at these altitudes, confirming the presence of minor warmings. Figure 3b shows the zonal-mean zonal wind, and there is no 10-hPa wind reversal until the final warming. In contrast to 1972, the 2002 REAN observations show both a reversal of the zonal-mean temperature gradient (Fig. 3c, black arrow) and a reversal of the zonal winds to easterlies (Fig. 3d, black arrow). Hence, the 1972 REAN data do not provide evidence of a major warming, while the 2002 data directly show a major stratospheric sudden warming.

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The REAN zonal-mean temperature difference between 60° and 90°S for (a) 1972 and (c) 2002, and the REAN zonal-mean 60°S zonal wind for (b) 1972 and (d) 2002. The thick black arrows indicate the appearance of the major stratospheric sudden warming in 2002. The thick red arrows indicate the stratospheric final warmings (a),(b) in late November 1972 and (c),(d) on 1 November 2002.

Citation: Journal of the Atmospheric Sciences 71, 12; 10.1175/JAS-D-14-0227.1

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In summary, station data provide only a limited ability to assess major stratospheric sudden warmings. Temperature fluctuations at specific locations are a result of both wave propagation effects and warming effects. The 1972 Molodezhnaya observations were of small value for understanding the strength of the mid- to lower-stratospheric jet and cannot be used to establish whether the midstratospheric flow reversed from westerlies to easterlies. Halley station is located in the core of the polar vortex and thereby provides direct evidence of a broad warming of the polar cap region (as is clear from the 2002 observations).

1. A major stratospheric warming is not apparent in 1972, as shown by Halley station data, an analysis of REAN data, and previously cited literature on SH major stratospheric sudden warmings (i.e., Barnett 1975).

2. The S1975 observations were not relevant to NN2005. The observations only had a slight temperature overlap at 30 km (the relevant region under the WMO definition of a major warming), they did not have the temporal and spatial resolution for observing a major stratospheric sudden warming, and they showed no reversal of the zonal-mean flow.

The S1975 and related papers were not cited in NN05 because they do not show evidence of a major stratospheric sudden warming. The S1975 data show temperature variations, but the source of these variations cannot be established.