Northern Hemisphere Values Research Articles

Carbon and hydrogen isotopic ratios of atmospheric methane in the upper troposphere over the Western Pacific

Abstract. We present the mixing ratio, δ13C and δD of atmospheric CH4 using commercial aircraft in the upper troposphere (UT) over the Western Pacific for the period December 2005–September 2010. The observed results were compared with those obtained using commercial container ships in the lower troposphere (LT) over the same region. In the Northern Hemisphere (NH), the UT CH4 mixing ratio shows high values in the boreal summer–autumn, when the LT CH4 mixing ratio reaches a seasonal minimum. From tagged tracer experiments made using an atmospheric chemistry transport model, we found that such high CH4 values are due to rapid transport of air masses influenced by CH4 sources in South Asia and East Asia. The observed isotopic ratio data imply that these areas have CH4 sources with relatively low δ13C and δD signatures such as biogenic sources. Latitudinal distributions of the annual average UT and LT CH4 mixing ratio intersect each other in the tropics; the mixing ratio value is lower in the UT than in the LT in the NH and the situation is reversed in the Southern Hemisphere (SH), due mainly to the NH air intrusion into the SH through the UT. Such intersection of the latitudinal distributions is observable in δD but not in δ13C, implying an additional contribution from reaction of CH4 with active chlorine in the marine boundary layer. δ13C and δD show low values in the NH and high values in the SH both in the UT and in the LT. We also observed an increase in the CH4 mixing ratio and decreases in δ13C and δ

Size-resolved chemical composition of Australian dust aerosol during winter

Environmental contextMineral dust aerosol is both an efficient scatterer of solar radiation, potentially cooling the planet, and a moderate absorber, potentially warming it: the exact balance is both uncertain, and geographically variable. Australian desert soils are noticeably more reddish than most Northern Hemisphere deserts, most probably a result of enhanced iron mineralogy. This paper contains results from a field campaign designed to increase our understanding of the chemistry of Australian mineral dust aerosol, especially in relation to iron and salt. AbstractAustralia is the dominant source of mineral dust aerosol in the Southern Hemisphere, yet the physical, chemical and optical properties of this aerosol remain poorly understood. Four sets of size-resolved aerosol samples were collected at a site on the edge of the Lake Eyre Basin (LEB), in the south-east dust transport pathway. Back trajectory analysis shows that three samples were sourced from the LEB (one during a rare winter dust storm), and one from coastal regions to the south. All samples were subjected to both ion beam analysis and ion chromatography. A Fe/Al ratio of 0.9 was found, consistent with results from our other campaigns to sites in the LEB, significantly higher than typical Northern Hemisphere values (~0.45–0.6). This confirms the iron-rich character of central Australian soils. Clear evidence of marine advection in the fourth sample was also found, and evidence of chloride depletion by nitric acid in two samples.

The great Sydney dust event: Size-resolved chemical composition and comparison

In September 2009, a major dust storm crossed eastern Australia, blanketing Sydney on two occasions. We collected size-resolved aerosol samples on both days, and have subjected them to Ion Beam Analysis at ANSTO. In this paper we present these results, and compare them with some of the analysis of similar samples obtained in field trips to the Lake Eyre Basin of central Australia, the primary source region of the dust. In particular, the Fe/Al ratios (∼0.9) are similar to LEB values, and higher than northern hemisphere values (∼0.55). Salt entrainment indicates a source near dry lakes.

Long‐term decrease in the global atmospheric burden of tetrachloroethene (C2Cl4)

We present a 14‐year record of tropospheric tetrachloroethene (C2Cl4) mixing ratios measured each season at remote surface locations throughout the Pacific Basin (71°N–47°S). Our calculated annual mean C2Cl4 mixing ratio for the extra‐tropical northern hemisphere (NH) was 13.9 ± 0.5 pptv in 1989, but declined to less than half this value (to 6.5 ± 0.2 pptv) by 2002. Mid‐latitude southern hemisphere (SH) mixing ratios, which were much smaller than NH values, showed interannual variations comparable to measured long‐term changes, and the SH annual mean was slightly less in 2002 than in 1989. Driven by the relatively large decrease in NH values, the global C2Cl4 mixing ratio declined from 6.3 ± 0.6 pptv in 1989 to 3.5 ± 0.2 pptv in 2002. These values suggest that the global C2Cl4 burden decreased by roughly 205 Gg between 1989–2002, which is consistent with industrial estimates of declining NH emissions over a similar period.

Interhemispheric linkage of paleoclimate during the last glaciation

Combined glacial geologic and palynologic data from the southern Lake District, Seno Reloncaví, and Isla Grande de Chiloé in middle latitudes (40°35’–42°25’S) of the Southern Hemisphere Andes suggest (1) that full‐glacial or near‐full‐glacial climate conditions persisted from about 29,400 to 14,550 14C yr BP in late Llanquihue time, (2) that within this late Llanquihue interval mean summer temperature was depressed 6°–8°C compared to modern values during major glacier advances into the outer moraine belt at 29,400, 26,760, 22,295–22,570, and 14,550–14,805 14C yr BP, (3) that summer temperature depression was as great during early Llanquihue as during late Llanquihue time, (4) that climate deteriorated from warmer conditions during the early part to colder conditions during the later part of middle Llanquihue time, (5) that superimposed on long‐term climate deterioration are Gramineae peaks on Isla Grande de Chiloé that represent cooling at 44,520–47,110 14C yr BP (T‐11), 32,105–35,764 14C yr BP (T‐9), 24,895–26,019 14C yr BP (T‐7), 21,430–22,774 14C yr BP (T‐5), and 13,040–15,200 14C yr BP (T‐3), (6) that the initial phase of the glacial/interglacial transition of the last termination involved at least two major steps, one beginning at 14,600 14C yr BP and another at 12,700–13,000 14 C yr BP, and (7) that a late‐glacial climate reversal of ≥2–3° C set in close to 12,200 14C yr BP, after an interval of near‐interglacial warmth, and continued into Younger Dryas time. The late‐glacial climate signal from the southern Chilean Lake District ties into that from proglacial Lago Mascardi in the nearby Argentine Andes, which shows rapid ice recession peaking at 12,400 14C yr BP, followed by a reversal of trend that culminated in Younger‐Dryas‐age glacier readvance at 11,400–10,200 14C yr BP.Many full‐ and late‐glacial climate shifts in the southern Lake District match those from New Zealand at nearly the same Southern Hemisphere middle latitudes. At the last glacial maximum (LGM), snowline lowering relative to present‐day values was nearly the same in the Southern Alps (875 m) and the Chilean Andes (1000 m). Particularly noteworthy are the new Younger‐Dryas‐age exposure dates of the Lake Misery moraines in Arthur's Pass in the Southern Alps. Moreover, pollen records from the Waikato lowlands on North Island show that a major vegetation shift at close to 14,700 14C yr BP marked the beginning of the last glacial/interglacial transition (Newnham et al. 1989).The synchronous and nearly uniform lowering of snowlines in Southern Hemisphere middle‐latitude mountains compared with Northern Hemisphere values suggests global cooling of about the same magnitude in both hemispheres at the LGM. When compared with paleoclimate records from the North Atlantic region, the middle‐latitude Southern Hemisphere terrestrial data imply interhemispheric symmetry of the structure and timing of the last glacial/interglacial transition. In both regions atmospheric warming pulses are implicated near the beginning of Oldest Dryas time (∼14,600 14C yr BP) and near the Oldest Dryas/Bölling transition (∼12,700–13,000 14 C yr BP). The second of these warming pulses was coincident with resumption of North Atlantic thermohaline circulation similar to that of the modern mode, with strong formation of Lower North Atlantic Deep Water in the Nordic Seas. In both regions, the maximum Bölling‐age warmth was achieved at 12,200–12,500 14 C yr BP, and was followed by a reversal in climate trend. In the North Atlantic region, and possibly in middle latitudes of the Southern Hemisphere, this reversal culminated in a Younger‐Dryas‐age cold pulse.Although changes in ocean circulation can redistribute heat between the hemispheres, they cannot alone account either for the synchronous planetary cooling of the LGM or for the synchronous interhemispheric warming steps of the abrupt glacial‐to‐interglacial transition. Instead, the dominant interhemispheric climate linkage must feature a global atmospheric signal. The most likely source of this signal is a change in the greenhouse content of the atmosphere. We speculate that the Oldest Dryas warming pulse originated from an increase in atmospheric water‐vapor production by half‐precession forcing in the tropics. The major thermohaline switch near the Oldest Dryas/Bölling transition then couldhave triggered another increase in tropical water‐vapor production to near‐interglacial values.

Seasonal and universal time distribution of patches in the northern and southern polar caps

Ion density measurements from the Dynamics Explorer 2 and Defense Meteorological Satellite Program F8 and F9 satellites are used to examine hemispherical differences in the occurrence patterns of polar ionization patches as a function of season, universal time (UT), and interplanetary magnetic field (IMF). When Bz<0, the greatest frequency of patch occurrence in the northern hemisphere is in the winter in the 1000–2200 UT range. This time corresponds to the interval when the northern magnetic pole (and hence the cusp) lies the farthermost toward the dayside. This fact is often used to explain the creation of patches in terms of the entrainment of dayside plasma into the cusp by high‐latitude convection. In the southern hemisphere we see that the occurrence frequencies peak at over twice the northern hemisphere values in the same general UT region (1000–2300 UT). However, the southern hemisphere cusp is most dayward at approximately 0300 UT, a time of minimum patch formation. Examination of the relationship of the terminator to the polar cap boundaries in each hemisphere leads to a simple explanation in terms of the differing offset of the magnetic poles (and the ionospheric convection pattern) from the geographic poles.

Icelandic Low Cyclone Activity: Climatological Features, Linkages with the NAO, and Relationships with Recent Changes in the Northern Hemisphere Circulation

Abstract Output from a cyclone detection and tracking algorithm, applied to twice-daily sea level pressure (SLP) fields for the period 1966–93, is used to examine the characteristics of cyclone activity associated with the locus of the mean Icelandic low (IL), variability during extremes of the North Atlantic oscillation (NAO), and recent changes in relation to circulation over the Northern Hemisphere. Cyclone events within the climatological IL display a modest seasonal cycle with a winter maximum. However, winter systems are considerably deeper than their summer counterparts with much larger maximum deepening rates. During the cold season (October–March), IL cyclone intensities are typical of oceanic systems but exhibit lower maximum deepening rates. During the warm season (April–September), intensities are typical of Northern Hemisphere values with deepening characteristics similar to those for all extratropical oceans. Depending on the month, 10%–15% (13%–18%) of cyclone events in the IL region repres...

An Estimate of Systematic Error and Uncertainty in Surface Cyclone Analysis over the North Pacific Ocean: Some Forecasting Implications

The systematic error and uncertainty of surface analyses produced by the National Meteorological Center (NMC) over the North Pacific Ocean is estimated. Differences in cyclone position, central pressure, and 12-h deepening rate between an operational manual analysis for the Northern Hemisphere (NH) and the automated initial analysis for the aviation run (AVN) of NMC's Global Forecast Model are compared, and their statistical significance is judged. The AVN central pressures are, on average, 2.2 mb higher than the NH values. The AVN initial maps underestimate cyclone intensity at all central pressures values, but the error is biggest (3.9 mb) for deep systems (central pressures ≤980 mb). The absolute displacement error averages 210 km with standard deviation of 200 km. Position errors are largest for weak systems (central pressures ≥1000 mb), averaging 300 km and being more than double the 140 km value for deep lows. The aggregate mean vector displacement of 10 km is negligible. Cyclone positions for the AVN initial maps agree to within 130 km of the NH locations for rapid deepening lows (12 h pressure change ≤ −12 mb), the smallest mean displacement error for any category examined. The life cycle of cyclones, as portrayed by the AVN initial charts, is too slow, with the AVN maps underestimating the 12-h deepening rate for rapid deepening lows by 5.4 mb, for all other deepening lows by 1.5 mb, and the 12-h filling rate for all cyclolytic lows by 2.4 millibars. Uncertainty in the central pressure and 12-h deepening rate, as measured by the width of confidence intervals, is largest for deep lows and for rapidly deepening cyclones, respectively, but the uncertainty in cyclone position is smallest for such systems. Weak lows or those undergoing little 12-h pressure change exhibit the greatest uncertainty in their position but they are more consistently defined in terms of central pressure. Implications of the uncertainty estimates on forecast verification and the generation of initial perturbations for ensemble forecasts are discussed.

Southern hemisphere tropospheric aerosol backscatter measurements—Implications for a laser wind system

Values of backscatter coefficient at 0.532 μm, 0.694 μm, and 10.6 μm were determined both by direct measurement and by Mie computation from measured aerosol microphysical properties in the eastern Australian region from 4°S to 41°S. Volume backscatter coefficients at 10.6 μm were typically in the range 1×10−11 to 3×10−11 m−1 sr−1 for both approaches, although the experimental uncertainty in both cases was quite large. Agreement between the shorter wavelength lidars and the aerosol data was typically within the combined experimental uncertainties, although direct measurements were systematically larger than values derived from the aerosol data; individual regions were observed where the disagreement was larger than the combined error. Backscatter at 10.6 μm and at visible wavelengths was found to be sensitive to essentially different regions of the aerosol size spectrum, questioning to some degree the validity of using short‐wavelength extinction and backscatter data to infer the global distribution of backscatter at wavelengths around 10.6 μm. Considerable day‐to‐day variability in backscatter was observed at all wavelengths. The implications of the very low backscatter values found, compared to northern hemisphere values, should be considered in the design of the Laser Atmospheric Wind Sounder (LAWS).

Assessing the Impact of Different Satellite Retrieval Methods on Forecast Available Potential Energy

The isentropic form for available potential energy (APE) is used to analyze the impact of the inclusion of satellite temperature retrieval data on forecasts made with the NASA Goddard Laboratory for Atmospheres (GLA) fourth order model. Two analysis datasets are used for the forecasts, one containing the NEDIS TIROSN retrievals and the other GLA retrievals using the physical inversion method. A third analysis dataset did not contain satellite data and was used as a control. Two analysis datasets, with and without satellite data, were used for verification. Northern Hemisphere values for the total APE show an increase throughout the 72 h forecast period for all three sets, mostly due to an increase in the zonal component, in contrast to the verification sets, which showed a steady level of total APE. The three forecast sets start with different values of total APE but by 36 h, the differences begin to diminish. At 72 h the total APE values for the three sets are almost identical. The magnitude of the total APE in the Southern Hemisphere does not increase in time and remains within the range of the verification sets. The vertically integrated grid point distributions of the eddy APE which provide geographical representations of baroclinic zones show little difference between the 0 h forecast fields and the analysis fields. At the end of the forecast period, however, there are moderate differences in the southern Pacific and Indian oceans. The grid point distributions of eddy APE are quite different among the three forecasts as well as the verification sets. In the Northern Hemisphere there are very pronounced differences in grid point distribution over Asia, the North Pacific Ocean and North America. These differences increase in area and magnitude as the forecast period progresses. They show coherence in their eastward progression with time across the eastern Pacific and North America. Examination of the grid point distributions indicates that the forecasts are slow, for example, in developing a low in the northern Rockies and never correctly capture its position or intensity. The differences noted above are a reflection of incorrect timing, position and/or magnitude. Isentropic cross sections for 50°N show that the lime lag exists around the entire parallel. The forecast set using the GLAS rerievals does somewhat better than the other sets in predicting intensity and position of developing lows, but all three forecasts resemble each other rather than the verification sets. This would seem to indicate that model characteristics are overwhelming any differences in the data sets.

Airborne measurements of stratospheric constituents over Antarctica in the Austral Spring, 1987: 2. Halogen and nitrogen trace gases

We have used a Fourier transform spectrometer aboard the NASA DC‐8 aircraft during the Airborne Antarctic Ozone Experiment to record infrared absorption spectra of the polar stratosphere. From these high‐resolution spectra we derived vertical column amounts above flight altitude of HCl, HF, NO, NO2, ClONO2, and HNO3 for 10 flights poleward of 60°S. Within the polar vortex, where low values of total ozone are observed during the latter part of the observation period, we observed markedly reduced columns of HCl, NO2, and HNO3. HCl values in the vortex were in the range of 3–9 × 1014 molecules cm−2, compared with values around 15–20 × 1014 molecules cm−2 in mid‐latitudes and ∼30×1014 molecules cm−2 in high northern latitudes. The ratio of HCl to HF was also abnormally low, implying that the HCl had been chemically or physically removed, rather than simply being redistributed by atmospheric motion. NO2 values within the inner vortex were near 5.0×1014 molecules cm−2, about a factor of 4 less than columns outside the vortex boundary. HNO3 values were lower by a factor of 3 within the vortex, compared with a column of approximately 15×1015 molecules cm−2 outside the vortex. HNO3 columns outside the vortex are similar to northern hemisphere values. The ClONO2 column was relatively large within the vortex, peaking at ∼30×1014 molecules cm−2 near the boundary of the vortex. An upper limit of ∼8×1014 molecules cm−2 is placed on the column amount of HOCl inside the vortex.

Latitudinal distributions of CO and CH4 over the Pacific

Measurements on Gametag (Global Atmospheric Measurements Experiment of Tropospheric Aerosols and Gases) in April and May 1978 indicate volume mixing ratios of CH4 of 1.62 ppmv south of the intertropical convergence zone and 1.72 ppmv north of 20°N. For CO south of 10°S, the CO volume mixing ratios were rather constant and equal to 57 ppbv. Poleward of 30°N in the northern hemisphere we measured average mixing ratios of 175 ppbv. Both for CO and for CH4 a gradual transition from lower southern hemispheric to higher northern hemispheric values were observed between 10°S and 20°N. The uncertainties in our measurements are 15% for CO and 3% for CH4. By comparing our observations with earlier ones (Seiler, 1974; Ehhalt, 1978), we can not detect any changes in the atmospheric abundances of CO and CH4 from 1972 to 1978 outside the uncertainty limits of the measurements.

Stratospheric CFCl3, CF2Cl2, and N2O height profile measurements at several latitudes

The mixing ratios of CFCl3, CF2Cl2, and N2O have been measured as a function of altitude from 6 to 37 km above sea level by using a balloon‐borne grab‐sampling system. The 24 flights were made during the period July 1976 to March 1979 from Wyoming, Panama, Brazil, and Antarctica. These data are reported here both numerically and graphically, the latter being examined for latitudinal and temporal trends. A mean tropopause height for each location and date was used as the reference for the height profiles. The resulting set of CF2Cl2 and N2O profiles show a discernible dependence on latitude; the lapse rate of these mixing ratios is greater for the mid‐latitudes when compared to the equatorial latitudes. The upper tropospheric portion of the CFCl3 and CF2Cl2 data show annual increases of 10.4±3.9 and 10.7±1.9%/yr, respectively, in the northern hemisphere for the middle of the measurement period (end of 1977). Furthermore, the limited number of southern hemispheric data for these constituents are about 8% lower than the northern hemispheric values but have a comparable annual increase. The corresponding N2O data show no interhemispheric differences and the possibility of only a slight increase (less than 2%/yr).

Atmospheric Halocarbons, Hydrocarbons, and Sulfur Hexafluoride: Global Distributions, Sources, and Sinks

The global distribution of fluorocarbon-12 and fluorocarbon-11 is used to establish a relatively fast interhemispheric exchange rate of 1 to 1.2 years. Atmospheric residence times of 65 to 70 years for fluorocarbon-12 and 40 to 45 years for fluorocarbon-l1 best fit the observational data. These residence times rule out the possibility of any significant missing sinks that may prevent these fluorocarbons from entering the stratosphere. Atmospheric measurements of methyl chloroform support an 8-to 10-year residence time and suggest global average hydroxyl radical (HO) concentrations of 3 x 10(5) to 4 x 10(5) molecules per cubic centimeter. These are a factor of 5 lower than predicted by models. Additionally, methyl chloroform global distribution supports Southern Hemispheric HO levels that are a factor of 1.5 or more larger than the Northern Hemispheric values. The long residence time and the rapid growth of methyl chloroform cause it to be a potentially significant depleter of stratospheric ozone. The oceanic sink for atmospheric carbon tetrachloride is about half as important as the stratospheric sink. A major source of methyl chloride (3 x 10(12)grams per year), sufficient to account for nearly all the atmospheric methyl chloride, has been identified in the ocean.

Preliminary estimation of average tropospheric HO concentrations in the northern and southern hemispheres

The global budget and hemispheric distribution of methyl chloroform (CH3CCl3) have been used to determine the average residence times of CH3CCl3, and HO radical concentrations, in the two hemispheres. It is concluded that a global average residence time (τa) of about 8 years best fits the observational data. It is further shown that the residence time of CH3CCl3 in the northern hemisphere (τn) is probably significantly longer than in the southern hemisphere (τs). While the ratio of τn/τs is quite sensitive to interhemispheric exchange rates (τe) and the north/south concentration gradients of CH3CCl3, a strong case for can nevertheless be made. Best estimates suggest that the global average HO concentration is most compatible with the observed data. The distribution of HO in the two hemispheres is, however, found to be asymmetric with southern hemispheric HO concentrations 1.6 to 3 times higher than the northern hemispheric values. It is inferred that this HO gradient is caused by atmospheric carbon monoxide, which is a principal sink for HO. The implications of these hemispheric HO asymmetries and the uncertainties involved are discussed.

Changes in atmospheric composition inferred from ionospheric production rates

Changes in the total electron content of the ionosphere near sunrise are used to determine the integrated production rate in the ionosphere ( Q) from 1965 to 1971, at latitudes of 34°S, 20°N and 34°N. The solar cycle change is given approximately by Q∝ S − 20, where S is the 10.7 cm solar flux. All stations show a regular semiannual variation in Q, through a range of 1.3:1. This is interpreted as an increase in the ratio O N 2 (the relative densities of atomic oxygen and molecular nitrogen) near the equinoxes. Northern hemisphere values of Q are nearly twice as large as southern hemisphere results, requiring an increase of about three times in the ratio O N 2 in the northern hemisphere. This ratio decreases in summer, near solar maximum, giving the well-known seasonal anomaly in the ionosphere. The seasonal change is larger at 34°N than at 20°N, and is completely absent at 34°S. Measurements of the time at which sunrise production begins confirm that the absorption of solar radiation is primarily by N 2 at all times at 34°S, but changes from N 2 in summer to atomic oxygen in winter in the northern hemisphere near solar maximum.