Northern Middle Latitudes Research Articles

The dynamically driven long‐term trend in stratospheric ozone over northern middle latitudes

AbstractThe cause of the observed mid‐latitude decline in ozone in a 20‐year integration of a stratospheric chemical transport model forced by European Centre for Medium‐Range Weather Forecasts analyses for the years 1979 to 1998 is investigated. A very simple chemical scheme for ozone is used which includes no interannual variation so that any modelled interannual variability, or trend, must arise from changes in the meteorology. The integration from 1979 to 1998 does show a downward trend in mid‐latitude ozone in which many of the observed features are reproduced, especially between the middle 1980s and the early 1990s. A detailed statistical trend analysis shows that the quantitative comparison between modelled and observed trend is very sensitive to the choice of period considered. However, there is good qualitative agreement in terms of the latitudinal variation of the trend. For the different periods considered, the dynamically driven model trend accounts for at least half of the observed northern mid‐latitude trend averaged over December to February. The vertical variation of the modelled and observed trends agree qualitatively. The modelled total ozone correlates well with the vertical winter EP‐flux at 100 hPa and the North Atlantic Oscillation index, suggesting that long‐term changes in stratospheric circulation are intimately connected to the observed mid‐latitude ozone trend. Copyright © 2002 Royal Meteorological Society.

The dynamically driven long-term trend in stratospheric ozone over northern middle latitudes

The dynamically driven long-term trend in stratospheric ozone over northern middle latitudes

Global behaviour of the ionosphere electron density using GPS observations

A large number of permanent GPS tracking stations have been established during the past years, most of them under the administration of the International GPS Service (IGS) (Beutler et al., 1999). On April 3, 1995, the MicroLab I (MLI) (Melbourne et al., 1994) satellite with a GPS receiver on board, was launched into a circular orbit of about 775 km of altitude and 60° of inclination. This experiment is named GPS-MET. Apart of other specific applications, the data of the terrestrial and spatial stations can also be used to study the ionosphere. The main goal of this kind of ionosphere research is to exploit the capability of these observations to continuously and routinely monitor the ionosphere at global scale. In particular, we will focus on the estimation of parameters describing the distribution of free electrons in the ionosphere. The electron density profiles introduced in this work are a new input to the ionosphere analysis with GPS observations. The possibility of having a space receiver that gives us information about the total electron content at different heights allows us to bring forward a model for the variation of the electron density with height. This model reflects the average and global behaviour of the ionosphere during the measured interval. We compare our profile with the IRI ones and find that there is better agreement at middle northern latitudes than low and middle southern latitudes.

Simulations of Permian Climate and Comparisons with Climate‐Sensitive Sediments

Abstract We use a climate model to simulate two intervals of Permian climate: the Sakmarian (ca. 280 Ma), at the end of the major Permo‐Carboniferous glaciation, and the Wordian (ca. 265 Ma). We explore the climate sensitivity to various levels of atmospheric CO2 concentration and to changes in geography and topography between the two periods. The model simulates large seasonality and high aridity in the continental interiors of both hemispheres for both periods. The northern summer monsoon weakens and the southern monsoon strengthens between the Sakmarian and the Wordian, owing to changes in geography and topography. The northern middle and high latitudes cool in winter, between the Sakmarian and Wordian, associated with northward shift of the continents. This high‐latitude cooling strengthens the winter westerlies and shifts the maximum storm‐track precipitation south. In the Southern Hemisphere, the winter westerlies weaken from the Sakmarian to the Wordian. Starting the simulations with no permanent i...

Impact of interannual meteorological variability on total ozone in northern middle latitudes: A statistical approach

The midwinter (January‐February) and summer (June‐July‐August) means of the total O3 derived from ground‐based measurements taken at northern midlatitudes are analyzed for the period 1963–1999. We use a simple, multiple, linear regression model to examine the ozone changes related to interannual meteorological variability. The explanatory variables of the model are selected from many variables characterizing the atmospheric circulation in the troposphere, the lowermost stratosphere, and the stratospheric overworld. The modeled time series of the midwinter and summer total ozone over Europe and North America show significant year‐to‐year variations corresponding to observed variations. Moreover, the model reproduces correlation between the summer (June‐July‐August) midlatitudinal ozone and its preceding midwinter (January‐February) value. The model calculates its lowest ozone amount during winter 1993. This follows the Mount Pinatubo eruption, but the ozone behavior can be explained as a result of dynamical variations only. The model‐observation agreement provides support for the hypothesis that the long‐term variations in total ozone over northern midlatitudes are strongly modulated by transport processes. It is estimated that interannual changes in the dynamical processes account for ∼70–80% of the long‐term ozone decline over the northern midlatitudes for the 1970–1997 period.

Characteristics of episodes with extremely low ozone values in the northern middle latitudes 1957−2000

Abstract. A number of episodes are observed when the total ozone for 2 to 3 days has fallen below 220 matm-cm in the northern mid- and polar latitudes in autumn. The occurrences of such episodes represent ozone deviations of about one-third from the pre-1976 Oct-Nov-Dec monthly mean! By using primarily quality checked Dobson data, a clear identification was made of more than three dozen short spells with extremely low ozone in the 1957–1978 period. In the following twenty-two years (1979–2000), using mainly TOMS data, one can identify ~ 46 cases with ozone values falling below 220 matm-cm for longer than 1 day, with each time over an area greater than 500,000 km2 . The Ozone Mass Deficiency (O3MD) from the pre-1976 average ozone values over the affected area was ~2.8 Mt per day, i.e. four to seven times greater than it would be, assuming only a long-term trend in the Oct-Nov-Dec period. The Extremely Low Ozone (ELO3) events on the day of their appearance over the N. Atlantic/European region contribute to the O3MD by representing 16% of the deficiency due to the Oct-Nov trend in the entire 40–65° N latitudinal belt. The O3MD of the greater pool with low ozone (here taken as <260 matm-cm) surrounding the area of the lowest events could contribute on the day of their appearance in Oct-Nov up to 60% and in December, ~30% to the deficiency due to the trend over the entire 40–65° N belt. Analysis of synoptic charts, supported by a backward trajectory on the isentropic surfaces 350 and 380 K, shows that in most of the events, subtropical air masses with low ozone content were transported from the Atlantic toward the UK, Scandinavia, and in many cases, further to the western sub-polar regions of Russia. This transport was sometimes combined with upward motions above a tropospheric anticyclone which lifted low ozone mixing ratios to higher altitudes. The ELO3 events cause a significant deficiency above the tropopause where, in general, the subtropical air is injected. In fact, the overall amount of ozone is not depleted, but redistributed on the hemispheric scale. Review of low ozone events, defined as days with negative deviations from the pre-1976 averages greater than 25% show, in general, similar origin. The seasonally averaged area with ELO3 and the associated O3MD, as well as for the cases with deviations > –25%, has increased during the 1990s, which could be an indication of stronger and/or more frequent subtropical air intrusions. Their occurrences could contribute noticeably to the ozone deficiency of the middle latitude ozone during the days of ELO3 appearances; however, their contribution to the long-term trend of the ozone seasonal decline is of the order of ~10%.Key words. Atmospheric composition and structure (middle atmosphere - composition and chemistry) Meteorology and atmospheric dynamics (middle atmosphere dynamics)

Latitudinal distribution of atmospheric CO2 sources and sinks inferred by δ13C measurements from 1985 to 1991

Net CO2 fluxes between the atmosphere and the ocean, and between the atmosphere and the terrestrial biosphere, were estimated by constraining a two‐dimensional atmospheric transport model with the CO2 concentration and its δ13C data obtained from our shipboard measurements in the western Pacific region during the period April 1984 to December 1991. The results obtained for the non‐El Niño and Southern Oscillation (ENSO) years during this time period showed that the ocean acted as a CO2 sink in middle latitudes of both hemispheres and a CO2 source around the equator. The results also suggested that during the 1984–1991 period there were biospheric CO2 sources in southern low and northern middle latitudes, and significant biospheric sinks in northern high latitudes. By comparing the latitudinal distributions of CO2 source/sink for ENSO years with those for non‐ENSO years, it was found that a considerable amount of CO2 was released from the terrestrial biosphere in low latitudes in association with the 1986–1987 ENSO event. While the oceanic region from the equator to 30°N acted as an excess CO2 sink of about 1.0 Gt C y−1r during 1987 and 1988, the oceanic contributions to the CO2 anomaly in the atmosphere were less pronounced in the northern high latitudes and in the southern hemisphere. Also, compared with the estimated interannual fluctuations in the atmosphere‐biosphere CO2 flux, the net CO2 flux between the atmosphere and the ocean showed relatively less interannual variability.

Calculation of daily tropospheric ozone residuals using TOMS and empirically improved SBUV measurements: Application to an ozone pollution episode over the eastern United States

A new technique for determining the integrated amount of ozone in the troposphere using concurrent observations from solar backscattered ultraviolet (SBUV) and Total Ozone Mapping Spectrometer (TOMS) data has been developed and is compared with various data sets. The technique makes use of the SBUV observations in the lowest three levels (1013‐63 mbar) of archived SBUV data to construct a climatology that is consistent with ozonesonde measurements. In the lowest layer (1013‐253 mbar), where ozone is almost always tropospheric, the SBUV measurements do not recreate the seasonality found in the ozonesonde data and consistently underestimate the amount of ozone at northern middle latitudes, the latitudes of interest for a later regional application. On the other hand, the key finding in this analysis shows that the integrated ozone amounts between 1013 and 63 mbar determined from SBUV are in good agreement with both the seasonality and the absolute ozone amount determined from the ozonesonde profiles. This result can then be used for determining a more accurate quantification of how much ozone is in both the troposphere and the stratosphere from any specific SBUV measurement. When used in conjunction with concurrent total ozone measurements from TOMS, we obtain better information about the distribution of ozone in the troposphere using the tropospheric ozone residual (TOR) technique. The TOR are then computed for the eastern United States during 1988 and compared to the ozonesonde measurements from Wallops Island during that year. The resultant comparison between the TOR and the Wallops Island measurements is considerably better using this technique when compared to calculated TOR values when the SBUV data are not corrected. The methodology is then applied to determine the large‐scale daily distribution of tropospheric ozone during times when surface concentrations of ozone were unusually high over vast regions on the eastern United States. These regional TOR patterns are analyzed in conjunction with various meteorological data sets and satellite imagery. Using such analyses, the relationship between the TOR distribution, meteorological processes in the lower troposphere, and the distribution of ozone at the surface during the 1988 episode is examined. This regional distribution of the TOR can be shown to be associated with the distribution of air masses that have evolved from the prevailing meteorological synoptic situation. The highest amounts of TOR are generally found off the coast of North Carolina and are consistent with the accumulation of ozone that had its origins over the northeastern United States and was subsequently advected southward off the North Carolina coast. The high TOR over the ocean is then caught in the persistent anticyclonic circulation where it becomes a source of ozone for the southeastern United States at a time when that region experiences numerous instances of surface ozone concentrations in violation of the Environmental Protection Agency hourly standards. When, over a period of several days, the dominating high‐pressure system over the eastern United States breaks down, TOR values decline, consistent with the fact that cleaner air of tropical origin is transported into the region.

Modelling climate response to historical land cover change

SummaryIn order to estimate the effect of historical land cover change (deforestation) on climate, we perform a set of experiments with a climate system model of intermediate complexity – CLIMBER‐2. We focus on the biophysical effect of the land cover change on climate and do not explicitly account for the biogeochemical effect. A dynamic scenario of deforestation during the last millennium is formulated based on the rates of land conversion to agriculture. The deforestation scenario causes a global cooling of 0.35 °C with a more notable cooling of the northern hemisphere (0.5 °C). The cooling is most pronounced in the northern middle and high latitudes, especially during the spring season. To compare the effect of deforestation on climate with other forcings, climate responses to the changing atmospheric CO2 concentration and solar irradiance are also analysed. When all three factors are taken into account, dynamics of northern hemisphere temperature during the last 300 years within the model are generally in agreement with the observed (reconstructed) temperature trend. We conclude that the impact of historical land cover changes on climate is comparable with the impact of the other climate forcings and that land cover forcing is important for reproducing historical climate change.

Atmospheric processes influencing measured carbon monoxide in the NASA Measurement of Air Pollution From Satellites (MAPS) experiment

The Measurement of Air Pollution From Satellites (MAPS) experiment measured global distributions of carbon monoxide (CO) while on board the space shuttle during April 9–19 and September 30 to October 11, 1994. This paper examines selected examples of the meteorological processes that contributed to the observed signals. We first examine and relate the mean distribution of MAPS‐measured CO, surface station‐measured CO, streamlines, and divergent winds averaged over the two missions. Tropical high CO values were associated with boundary layer convergence regions, particularly in October, that enable CO associated with biomass burning to reach the free troposphere where it can be detected by the nadir viewing gas filter 4.7 μm radiometer. CO values over northern middle latitudes show evidence of fossil fuel pollution especially in April. Southern middle and high latitudes in April suggest photochemical control, while in October these regions are strongly influenced by the tropical biomass burning. Next, we consider events on 1 day near the center of each mission and show that in one of these cases, low CO measurements are associated with high potential vorticity, which suggests that the air samples originated from the stratosphere. Finally, we modify the two mean patterns, both within 23 days of the equinox, to illustrate the possible separation of the natural photochemical CO pattern from the CO pollution patterns. This procedure brings out the intercontinental and transcontinental transport of pollution in April northern hemisphere middle and high latitudes as well as, less markedly, in the October maps. It also accentuates the biomass burning contribution in October and shows pollution to extend southeastward from South America into the South Atlantic and also from Australia into the South Pacific. The separation is made possible by having CO measurements with global coverage.

Ionospheric measurements during the CRISTA/MAHRSI campaign: their implications and comparison with previous campaigns

Abstract. The CRISTA/MAHRSI experiment on board a space shuttle was accompanied by a broad campaign of rocket, balloon and ground-based measurements. Supporting lower ionospheric ground-based measurements were run in Europe and Eastern Asia between 1 October-30 November, 1994. Results of comparisons with long ionospheric data series together with short-term comparisons inside the interval October-November, 1994, showed that the upper middle atmosphere (h = 80-100 km) at middle latitudes of the Northern Hemisphere in the interval of the CRISTA/MAHRSI experiment (4-12 November, 1994) was very close to its expected climatological state. In other words, the average results of the experiment can be used as climatological data, at least for the given area/altitudes. The role of solar/geomagnetic and "meteorological" control of the lower ionosphere is investigated and compared with the results of MAP/WINE, MAC/SINE and DYANA campaigns. The effects of both solar/geomagnetic and global meteorological factors on the lower ionosphere are found to be weak during autumn 1994 compared to those in MAP/WINE and DYANA winters, and they are even slightly weaker than those in MAP/SINE summer. The comparison of the four campaigns suggests the following overall pattern: in winter the lower ionosphere at northern middle latitudes appears to be fairly well "meteorologically" controlled with a very weak solar influence. In summer, solar influence is somewhat stronger and dominates the weak "meteorological" influence, but the overall solar/meteorological control is weaker than in winter. In autumn we find the weakest overall solar/meteorological control, local effects evidently dominate.Key words. Ionosphere (ionosphere · atmosphere interactions; mid-latitude ionosphere)

An analysis of ozonesonde data for the troposphere: Recommendations for testing 3‐D models and development of a gridded climatology for tropospheric ozone

I present an analysis of ozonesonde data, synthesizing what is known about the distribution of tropospheric ozone. Major features of the distribution are highlighted, and recommendations are given for testing three‐dimensional models of tropospheric chemistry and transport with these data. The data are analyzed on pressure surfaces and relative to the height of the thermal tropopause. A minimum of 20 soundings are required for 95% confidence intervals of the ozone monthly means to be less than ±30% near the extratropical tropopause. Twenty soundings also ensures means reliable to better than ±15% for 800–500 hPa for the extratropics and for 800–100 hPa in the tropics. Ozone variability is higher in the upper troposphere for subtropical locations than for tropical locations, and 35 soundings are required for 400–100 hPa for the means to be defined to better than ±15%. For northern middle and high latitudes, the broad summer maximum in ozone in the middle troposphere extends all the way up to the tropopause. Median concentrations at the tropopause are highest in June and July, typically 125–200 ppb, and are a factor of 2 smaller in winter. Highest values of ozone are in spring 2 km above the tropopause. The change in the phase of the annual cycle of ozone between the tropopause and the region immediately above it, and the steep concentration gradients across the tropopause, suggest that high vertical resolution (∼1 km) will be required in models to simulate this behavior. Mean ozone values in the middle troposphere are approximately constant from 30° to 75° in the winter in both hemispheres, while there is a maximum from 35° to 50°N in summer. In the northern subtropics, there is a summer minimum in middle tropospheric ozone over the Pacific and a summer maximum over the Atlantic which appear to be related to differences in circulation. Mean ozone values over Samoa are similar to those measured 20–30 years ago over Panama. Ozone is higher over the tropical South Atlantic (Natal) than over the western Pacific (Samoa) all year from about 800 hPa to the tropopause; ozone is most similar in May and June over the Atlantic and Pacific, the months with minimum burning in the tropics. The ozone maximum at Samoa in the middle and upper troposphere in October is caused by long‐range transport of ozone and its precursors from biomass burning, with the peak lagging that at Natal by about a month. The secondary peak in ozone in January and December at South Atlantic sites reflects transport of biomass burning effluents from the Northern Hemisphere. The sonde data were used in combination with surface and satellite data to derive a gridded climatology for tropospheric ozone.

Atmospheric chloroform

Chloroform is one of several chlorine-containing gases in the atmosphere that by themselves are unimportant in the chlorine budget of the Earth’s atmosphere, but may be significant if taken together. We present a nine-year time series of concentrations at the surface of the polar, middle, and tropical latitudes of both hemisphere. These and related data establish its seasonal, latitudinal, and altitudinal concentrations. The average concentration observed at the surface is 18.5 pptv, but at some continental locations annual averages can reach 40 pptv. The atmospheric lifetime of chloroform is short at about 0.5 yr due to reactions with OH and may be shorter if other removal processes exist. No significant trends were observed during the last decade. Using these data we calculate that the global emission rate must be about 470 (350–600) Gg yr -1 with about 70% emitted in the northern middle and tropical latitudes.

Transient climate change and net ecosystem production of the terrestrial biosphere

In this sensitivity study, we have applied the Terrestrial Ecosystem Model ((TEM) version 4.1) to examine the responses of terrestrial ecosystems to transient changes in atmospheric CO2 concentration and climate in the 21st century at the scales of the globe, biomes, latitudinal gradient, and economic regions. Three predictions of transient change in climate and atmospheric CO2 concentration in the 21st century from the Integrated Global System Model developed at Massachusetts Institute of Technology were used. The TEM estimates a global annual net ecosystem production (NEP) of about 0.8 Pg C yr−1 in 1990. Global annual NEP in 2100 increases by about 2.6 Pg C yr−1 for the HHL (higher CO2 emissions and temperature increases), 1.8 Pg C yr−1 for the RRR (reference CO2 emissions and temperature increases), and 0.5 Pg C yr−1 for the LLH (lower CO2 emissions and temperature increases) climate change predictions. The boreal and tropical evergreen forests account for a large portion of the increased global annual NEP. Latitudinal distribution of total annual NEP along 0.5°‐resolution latitudinal bands shifts significantly from the tropics to the northern middle and high latitudes over time. The potential CO2 uptake over the period of 1990–2100 differs substantially among the 12 economic regions of the world. As we used potential mature natural vegetation in the global extrapolation of TEM, these NEP estimates represent the potential CO2 uptake or the upper bound for long‐term carbon sequestration by the terrestrial biosphere. This sensitivity study shows that the temporal dynamics and spatial distribution of carbon, nitrogen, and water fluxes of terrestrial ecosystems are very sensitive to the magnitudes and paths of transient changes in atmospheric CO2 concentration and climate in the 21st century.

First observation of quasi-2-day oscillations in ionospheric plasma frequency at fixed heights

Abstract. The existence and development of the quasi-2-day oscillations in the plasma frequency variations of the F region at northern middle latitudes are investigated. A new approach to study the quasi-2-day oscillations is presented, using a methodology that allows us to do such a study at fixed heights. The hourly values of plasma frequency at fixed heights, from 170 km to 220 km at 10 km step, obtained at the Observatori de l'Ebre station (40.8°N, 0.5°E) during 1995 are used for analysis. It is found that quasi-2-day oscillations exist and persisted in the ionospheric plasma frequency variations over the entire year 1995 for all altitudes investigated. The dominant period of oscillation ranges from 42 to 56 h. The amplitude of oscillation is from 0.1 MHz to 1 MHz. The activity of the quasi-2-day oscillation is better expressed during the summer half year when several enhancements, about 15–30 days in duration, were observed. The largest enhancements of the oscillation occurred during early June, July and early August; i. e., near and after the summer solstice when the 2-day wave in the middle neutral atmosphere typically displays its largest activity in the Northern Hemisphere. The results obtained may help us understand better the possible influencing mechanisms between the 2-day wave in the middle neutral atmosphere and the ionospheric quasi-2-day oscillations.Key words. Ionosphere (Ionosphere - atmosphere interactions; Mid-latitude ionosphere; Plasma waves and instabilities)

Spectral energy contributions of quasi-periodic oscillations (2-35 days) to the variability of the f<sub>o</sub>F2

Abstract. The relative contributions of quasi-periodic oscillations from 2 to 35 days to the variability of foF2 at middle northern latitudes between 42°N and 60°N are investigated. The foF2 hourly data for the whole solar cycle 21 (1976–1986) for four European ionospheric stations Rome (41.9°N, 12.5°E), Poitiers (46.5°N, 0.3°E), Kaliningrad (54.7°N, 20.6°E) and Uppsala (59.8°N, 17.6°E) are used for analysis. The relative contributions of different periodic bands due to planetary wave activity and solar flux variations are evaluated by integrated percent contributions of spectral energy for these bands. The observations suggest that a clearly expressed seasonal variation of percent contributions exists with maximum at summer solstice and minimum at winter solstice for all periodic bands. The contributions for summer increase when the latitude increases. The contributions are modulated by the solar cycle and simultaneously influenced by the long-term geomagnetic activity variations. The greater percentage of spectral energy between 2 to 35 days is contributed by the periodic bands related to the middle atmosphere planetary wave activity.Key words. Ionosphere · Ionosphere-atmosphere interactions · Mid-latitude ionosphere · Plasma waves and instabilities

First observation of quasi-2-day oscillations in ionospheric plasma frequency at fixed heights

The existence and development of the quasi-2-day oscillations in the plasma frequency variations of the F region at northern middle latitudes are investigated. A new approach to study the quasi-2-day oscillations is presented, using a methodology that allows us to do such a study at fixed heights. The hourly values of plasma frequency at fixed heights, from 170 km to 220 km at 10 km step, obtained at the Observatori de l'Ebre station (40.8°N, 0.5°E) during 1995 are used for analysis. It is found that quasi-2-day oscillations exist and persisted in the ionospheric plasma frequency variations over the entire year 1995 for all altitudes investigated. The dominant period of oscillation ranges from 42 to 56 h. The amplitude of oscillation is from 0.1 MHz to 1 MHz. The activity of the quasi-2-day oscillation is better expressed during the summer half year when several enhancements, about 15–30 days in duration, were observed. The largest enhancements of the oscillation occurred during early June, July and early August; i. e., near and after the summer solstice when the 2-day wave in the middle neutral atmosphere typically displays its largest activity in the Northern Hemisphere. The results obtained may help us understand better the possible influencing mechanisms between the 2-day wave in the middle neutral atmosphere and the ionospheric quasi-2-day oscillations.Key words. Ionosphere (Ionosphere - atmosphere interactions; Mid-latitude ionosphere; Plasma waves and instabilities)

Characteristics of the ozone decline in the northern polar and middle latitudes during the winter-spring

The total ozone decline during the past twenty years, especially strong during the winter-spring season poleward from 50° N, is well established with known average trends of 5–7% per decade. This study presents a number of additional characteristics such as ozone-mass deficiency (O3MD) from the pre- 1976 base average, and areal extent with negative deviations greater than∼2 and∼3δ. Gridded satellite data combined with ground-based total ozone maps, permit calculations of daily and regional ozone deficiencies from the anthropogenically undisturbed average ozone levels of the 1960s and early 1970s. Then the quantity of the O3MD and the changes in surface area, with deficiencies larger than-10 and-15% are integrated for the 1 January to 15 April period for each of the last 20 years, and compared. In addition, the polar vortex extent during the last 10 years is determined using the PV at 475°K. The quantity of the O3MD within the sunlit part of the vortex is shown to contribute from∼15 to 35% of the overall ozone deficiency within the-10% contours over the area 35–90°N. The ozone deficiency, integrated for the first 105 days of each year, has increased dramatically from ∼2,800Mt in the early 1980s to∼7,800Mt in the 1990s, exceeded 12,000Mt in the winter-springs of 1993 and 1995. The latter quantity is comparable with the average O3MD over the same Southern latitudes in the last ten austral springs. During the 1990s over the 35–90° latitudes the average ozone deficiency in the Southern hemisphere belt is less than over the Northern hemisphere belt by∼40%. It is known that the main ozone decline is observed in the lower stratosphere and the ozone loss over the Arctic is very sensitive to decreasing stratospheric temperatures; negative 50hPa monthly anomalies greater than 4°C have occurred during 7 of the springs in the last decade, thus possibly facilitating doubling the area with negative ozone deviations greater than-10% in the 1990s to∼5,000.106km2 and nearly tripling the O3MD as stated above. The changes in total eddy heat fluxes as a proxy indicator of the long wave perturbations are positively correlated with the ozone deficiency in the 45–75°N. The strong anticorrelation between the ozone deficiency in the region>55° N. versus the 35–50° N belt is discussed in relation to possible transport of air masses with low ozone from the sub-tropics, which in some years are the dominant reason for the observed ozone deficiency.

Local upper tropospheric/lower stratospheric clear‐sky water vapor and tropospheric deep convection

Local upper tropospheric and stratospheric water vapor profile retrievals by Stratospheric Aerosol and Gas Experiment II for July 1986–1990 are compared with concurrent International Satellite Cloud Climatology Project deep convective clouds to investigate the possible impact of deep convection on upper level moisture distributions. Results show that at low latitudes, clear‐sky water vapor values in the upper troposphere (above 300 mbar level) decrease following the onset of convection, perhaps because of compensatory subsidence. The drying lasts for a few hours and then is interrupted by a moistening trend centered at 6 hours after the convection breaks out, perhaps because of the detrainment of cloud liquid water from the convective tower and spreading anvil clouds. From about 9 hours later the tropical lower stratosphere shows moistening occurring. Largely because of these effects, the tropical lower stratosphere has 20–30% more moisture at sunrise compared to sunset. The later stratospheric moistening has the largest correlation significance with convection as well as the largest sampling number, though the absolute variation is much less than the variation in the troposphere. At northern hemisphere summer middle latitudes, upper tropospheric drying follows moist convection events, without an obvious moistening trend in the upper troposphere and impact in the stratosphere. The results indicate that the relationship between local upper tropospheric moisture and convective events is timescale and latitude dependent. They illustrate the utility of high vertical and temporal resolution data for proper averaging and interpretation of convection and water vapor studies.

Palaeoenvironmental significance of grus weathering profiles: a review with special reference to northern and central Europe

Grus weathering profiles are common signs of bedrock alteration in northern middle and high latitudes and have frequently been used to infer climatic regimes of the past and to develop denudation chronologies. This paper shows that the actual palaeoenvironmental significance of grus weathering is limited, and its potential in such reconstructions is clearly conditioned by local situations. Textural and mineralogical features of grus weathering profiles are rather unreliable indicators of past environments, being influenced by a variety of factors, including parent rock characteristics, topography and geological and geomorphological history. Grus weathering has been operating for at least the last few million years and the known profiles are of different ages, so it is doubtful if there is any narrow range of climatic conditions to which the origin of grus may be ascribed. By contrast, the relatively neglected relationships between grus weathering and topography at different scales of inquiry may be worthy of exploration, because it may help to decipher evolutionary pathways of weathering profiles.