Mean Seasonal Variation Research Articles

Air–sea CO<sub>2</sub> flux in the Pacific Ocean for the period 1990–2009

Abstract. Air–sea CO2 fluxes over the Pacific Ocean are known to be characterized by coherent large-scale structures that reflect not only ocean subduction and upwelling patterns, but also the combined effects of wind-driven gas exchange and biology. On the largest scales, a large net CO2 influx into the extratropics is associated with a robust seasonal cycle, and a large net CO2 efflux from the tropics is associated with substantial interannual variability. In this work, we have synthesized estimates of the net air–sea CO2 flux from a variety of products, drawing upon a variety of approaches in three sub-basins of the Pacific Ocean, i.e., the North Pacific extratropics (18–66° N), the tropical Pacific (18° S–18° N), and the South Pacific extratropics (44.5–18° S). These approaches include those based on the measurements of CO2 partial pressure in surface seawater (pCO2sw), inversions of ocean-interior CO2 data, forward ocean biogeochemistry models embedded in the ocean general circulation models (OBGCMs), a model with assimilation of pCO2sw data, and inversions of atmospheric CO2 measurements. Long-term means, interannual variations and mean seasonal variations of the regionally integrated fluxes were compared in each of the sub-basins over the last two decades, spanning the period from 1990 through 2009. A simple average of the long-term mean fluxes obtained with surface water pCO2 diagnostics and those obtained with ocean-interior CO2 inversions are −0.47 ± 0.13 Pg C yr−1 in the North Pacific extratropics, +0.44 ± 0.14 Pg C yr−1 in the tropical Pacific, and −0.37 ± 0.08 Pg C yr−1 in the South Pacific extratropics, where positive fluxes are into the atmosphere. This suggests that approximately half of the CO2 taken up over the North and South Pacific extratropics is released back to the atmosphere from the tropical Pacific. These estimates of the regional fluxes are also supported by the estimates from OBGCMs after adding the riverine CO2 flux, i.e., −0.49 ± 0.02 Pg C yr−1 in the North Pacific extratropics, +0.41 ± 0.05 Pg C yr−1 in the tropical Pacific, and −0.39 ± 0.11 Pg C yr−1 in the South Pacific extratropics. The estimates from the atmospheric CO2 inversions show large variations amongst different inversion systems, but their median fluxes are consistent with the estimates from climatological pCO2sw data and pCO2sw diagnostics. In the South Pacific extratropics, where CO2 variations in the surface and ocean interior are severely undersampled, the difference in the air–sea CO2 flux estimates between the diagnostic models and ocean-interior CO2 inversions is larger (0.18 Pg C yr−1). The range of estimates from forward OBGCMs is also large (−0.19 to −0.72 Pg C yr−1). Regarding interannual variability of air–sea CO2 fluxes, positive and negative anomalies are evident in the tropical Pacific during the cold and warm events of the El Niño–Southern Oscillation in the estimates from pCO2sw diagnostic models and from OBGCMs. They are consistent in phase with the Southern Oscillation Index, but the peak-to-peak amplitudes tend to be higher in OBGCMs (0.40 ± 0.09 Pg C yr−1) than in the diagnostic models (0.27 ± 0.07 Pg C yr−1).

Alaska tidewater glacier terminus positions, 1948–2012

A significant portion of the world's glacier ice drains through tidewater outlets, though much remains unknown about the response to recent climate change of tidewater glaciers. We present a 64 year record of length change for 50 Alaska tidewater glaciers. We use U.S. Geological Survey topographic maps to provide a base length for glaciers before 1970. Using all available cloud‐free Landsat images, we manually digitize calving front outlines for each glacier between 1972 and 2012, resulting in a total of more than 10,000 outlines. Tidewater glacier lengths vary seasonally; focusing on the 36 glaciers terminating in tidewater throughout the study period, we find a mean (± standard deviation) seasonal variation of 60± 85 m a−1. We use these oscillations to determine the significance of interannual changes in glacier length. All 36 glaciers underwent at least one period (≥1 year) of significant advance or retreat; 28 glaciers underwent at least one period of both significant advance and retreat. Over the entire period 1948–2012, 24 of these glaciers retreated a total (± uncertainty) of 107.95±0.29 km, 11 advanced a total of 7.71±0.20, and one (Chenega Glacier) did not change significantly. Retreats and advances are highly variable in time; several glaciers underwent rapid, short‐term retreats of a few years duration. These retreats occurred after large changes in summer sea surface temperature anomalies; further study is needed to determine what triggered these retreats. No coherent regional behavior signal is apparent in the length record, although two subregions show a coherence similar to recent observations in Greenland.

Impact of quasi-biennial oscillation on the inter-annual variability of the tropopause height and temperature in the tropics: A study using COSMIC/FORMOSAT-3 observations

The effect of quasi-biennial oscillation (QBO) on the temperature of cold point tropopause (T-CPT) and its height (H-CPT) is being investigated using radio occultation measurements by COSMIC/FORMOSAT-3. Observations comprising of 935,863 numbers of occultations have been used to study the zonal mean seasonal variability in T-CPT and H-CPT from January 2007 to December 2011. Results are shown over 30°N–30°S geographic latitudes. In general, T-CPT is found to be the coldest in February and the warmest in August. H-CPT attains maximum height during December–February and minimum during July–August. Interestingly, H-CPT shows maxima at off-equator region (around 20°N or 20°S) during all the seasons in both hemispheres. H-CPT at off-equatorial region, in reference to the equatorial region, is slightly higher (~1.0km) during winter as compared to monsoon season (~0.5km) in Northern Hemisphere (NH). Inter-annual variation in T-CPT and H-CPT found to be clearly influenced by the QBO. Westerly (easterly) phase generates warm (cold) T-CPT, which consequently results a decrease (increase) in H-CPT. It is concluded that QBO induces the changes in T-CPT by as much as 2°C and in H-CPT by 0.5km.

Sea level variation from a remote river in the Gulf of Paria, Trinidad

Short-term sea level variability is investigated by analytical methods to ascertain whether there is a link between peak tidal residuals in the Gulf of Paria (GoP), Trinidad, and peak river outflow from the Orinoco on the Venezuelan mainland. Analysis of tidal data suggests that although the Orinoco delta fronts the Atlantic ocean, significant volumes of this river runoff enter into the GoP and play a role in seasonal sea level variation on the western coastline of the southernmost Caribbean island of Trinidad. The indications from various statistical analyses including harmonic, spectral and time series analyses of tide gauge data are that mean seasonal variations in water level in the north of the GoP exhibit a positive temporal correlation between the tidal residuals and the peak river discharge associated with the Orinoco's seasonal cycle. The maximal de-tided residuals are strongly correlated with maximal values of the river runoff, as well as the discharge trend, with the residual values at initial average estimates of about 12–15 cm/year.

Analysis of the variability of temperature gradient in the ocean frontal zones based on satellite data

AVHRR MCSST data for the periods 1982–2000 (mean weekly data) were used to calculate mean gradient fields in the ocean for different periods of time. Three-month averaged sea surface temperature gradients (SSTG) and their mean seasonal variations have been studied for 25 points in the large-scale oceanic fronts zones. Major oceanic fronts in the Atlantic and Pacific have been identified and compared in literature. In the North Atlantic and Pacific, the areas under study were the North Polar Front and Subpolar Fronts. In the South Atlantic and Pacific we studied the region of the Antarctic Circumpolar Current (ACC) and the fronts formed by this current, known as the South Polar Front, and the Subantarctic Front. SSTG were also calculated for El Niño (Southeast Pacific) and Benguela Current (Southeast Atlantic).In warm periods seasonal SSTG in the North Atlantic markedly increased and exhibit some interannual cycles. The correlation between the North Atlantic Oscillation index and seasonal SSTG for a single point in the Gulf Stream zone can be the key point for evaluation of heat transfer by the currents to the coast of East Europe.In the Southern Atlantic, the SSTG values are low during the cold period (summer in the southern hemisphere) in the ACC zone and increase in the warm season (winter in the southern hemisphere). It also exhibits interannual cycles.In the Northwest Pacific for some points in the Subpolar Front the SSTG values are high in the cold period (winter). Here at seven points in the spring of 1993 and 2000 the calculations disclosed significant increase of the gradient. In these years, the anomalous SSTG in Subpolar Front and South Polar Front were found to vary synchronously in both hemispheres, with maximum intensity in spring (North Pacific) and in summer (South Pacific).Mean annual SSTG in the El Niño zone and south oscillation index have been found to exhibit some correlation.Major jet currents periodically form high-gradient temperature fields and from the temperature satellite data we can derive information about variation in the large-scale fronts in the Global Ocean.

Characterization of GPS total electron content (GPS-TEC) in Antarctica from 2004 to 2011

<p>The vertical total electron content (VTEC) obtained from 2004 to 2011 at Comandante Ferraz Brazilian Antarctic Station (62.1°S, 58.4°W) is analyzed to study the mean diurnal, seasonal and annual variations. The maximum daytime VTEC had an annual variation that decreased from 2004 to 2008, and then starting to increase in 2009, which followed the variation of the solar activity. The daily VTEC shows good linear correlation with solar radiation intensity, which is also dependent on the solar zenithal angle. The mean diurnal VTEC shows a semiannual variation, with larger peaks in equinoxes for all years; no winter anomaly was observed, and in summer, there was no clear diurnal variation. The semiannual variation of the VTEC is also modulated by solar activity, with larger VTEC peaks when the solar activity was higher.</p>

Ozone variations over the northern subtropical region revealed by ozonesonde observations in Hanoi

Seasonal and subseasonal variations in the ozone mixing ratio (OMR) are investigated by using continuous 7 year ozonesonde data from Hanoi (21°N, 106°E), Vietnam. The mean seasonal variations for the 7 years show large amplitude at the upper troposphere and lower stratosphere (UTLS) region (10–18 km) and at the lower troposphere (around 3 km) with standard deviations normalized by the annual mean value of about 30% for both regions. In the UTLS region, the seasonal variation in the OMR shows a minimum in winter and a maximum in spring to summer. The variation seems to be caused by the seasonal change in horizontal transport. Low OMR air masses are transported from the equatorial troposphere in winter by the anticyclonic flow associated with the equatorial convections, and high OMR air masses are transported from the midlatitude stratosphere in summer possibly due to Rossby wave breakings in the UT region and anticyclonic circulation associated with the Tibetan High in the LS region. In the lower troposphere, a spring maximum is found at 3 km height. Biomass burning and tropopause foldings are suggested as possible causes of this maximum. Subseasonal variations in the OMR show large amplitude in the UTLS region (at around 15 km) and in the boundary layer (below 1 km) with the standard deviations normalized by the annual mean larger than 40%. The OMR variations in the winter UTLS region have a negative correlation with the meridional wind. This relation indicates that the low OMRs observed at Hanoi has been transported from the equatorial region.

Investigating the Use of a Genesis Potential Index for Tropical Cyclones in the North Atlantic Basin

AbstractLarge-scale environmental variables known to be linked to the formation of tropical cyclones have previously been used to develop empirical indices as proxies for assessing cyclone frequency from large-scale analyses or model simulations. Here the authors examine the ability of two recent indices, the genesis potential (GP) and the genesis potential index, to reproduce observed North Atlantic cyclone annual frequency variations and trends. These skillfully estimate the mean seasonal variation of observed cyclones, but they struggle with reproducing interannual frequency variability and change. Examination of the independent contributions by the four terms that make up the indices finds that potential intensity and shear have significant skill, while moisture and vorticity either do not contribute to or degrade the indices’ capacity to reproduce observed interannual variability. It is also found that for assessing basinwide cyclone frequency, averaging indices over the whole basin is less skillful than its application to the general area off the coast of Africa broadly covering the main development region (MDR).These results point to a revised index, the cyclone genesis index (CGI), which comprises only potential intensity and vertical shear. Application of the CGI averaged over the MDR demonstrates high and significant skill at reproducing interannual variations and trends in all-basin cyclones across both reanalyses. The CGI also provides a more accurate reproduction of seasonal variations than the original GP. Future work applying the CGI to other tropical cyclone basins and to the downscaling of relatively course climate simulations is briefly addressed.

Exploring the physical controls of regional patterns of flow duration curves – Part 2: Role of seasonality, the regime curve, and associated process controls

Abstract. The goal of this paper is to explore the process controls underpinning regional patterns of variations of streamflow regime behavior, i.e., the mean seasonal variation of streamflow within the year, across the continental United States. The ultimate motivation is to use the resulting process understanding to generate insights into the physical controls of another signature of streamflow variability, namely the flow duration curve (FDC). The construction of the FDC removes the time dependence of flows. Thus in order to better understand the physical controls in regions that exhibit strong seasonal dependence, the regime curve (RC), which is closely connected to the FDC, is studied in this paper and later linked back to the FDC. To achieve these aims a top-down modeling approach is adopted; we start with a simple two-stage bucket model, which is systematically enhanced through addition of new processes on the basis of model performance assessment in relation to observations, using rainfall-runoff data from 197 United States catchments belonging to the MOPEX dataset. Exploration of dominant processes and the determination of required model complexity are carried out through model-based sensitivity analyses, guided by a performance metric. Results indicated systematic regional trends in dominant processes: snowmelt was a key process control in cold mountainous catchments in the north and north-west, whereas snowmelt and vegetation cover dynamics were key controls in the north-east; seasonal vegetation cover dynamics (phenology and interception) were important along the Appalachian mountain range in the east. A simple two-bucket model (with no other additions) was found to be adequate in warm humid catchments along the west coast and in the south-east, with both regions exhibiting strong seasonality, whereas much more complex models are needed in the dry south and south-west. Agricultural catchments in the mid-west were found to be difficult to predict with the use of simple lumped models, due to the strong influence of human activities. Overall, these process controls arose from general east-west (seasonality) and north-south (aridity, temperature) trends in climate (with some exceptions), compounded by complex dynamics of vegetation cover and to a less extent by landscape factors (soils, geology and topography).

The cause of the seasonal variation in the oxygen isotopic composition of precipitation along the western U.S. coast

This study seeks to find the primary influence on the seasonal cycle of the oxygen isotopic composition of precipitation (δ18Op) along the western U.S. coast. Observed long‐term mean seasonal variations ofδ18Op from 16 different stations along the west coast are presented. The most robust features in the observations are high values in the summer and a drop in δ18Opduring the winter. The Isotope‐incorporated Global Spectral Model (IsoGSM) also simulates this wintertime drop inδ18Op along the west coast of the U.S. Sensitivity experiments are performed with IsoGSM where individual oxygen isotope fractionation processes are turned off. These simulations reveal that the primary control on the seasonal variations is equilibrium oxygen isotopic fractionation during vapor condensation. There is almost no influence of the temperature dependence of equilibrium fractionation on the seasonal δ18Op cycle for both evaporation and condensation. Additional experiments (including tagging simulations) are performed to better understand why Rayleigh distillation causes the seasonal variation in δ18Op. The tagging simulations and budget calculations reveal that vertical oxygen isotope gradients and variations in condensation height cause the seasonal cycle in δ18Op. This results from seasonal changes in the polar jet, and subsequent changes to divergence and vertical velocities, which affects the uplift of moisture. These findings suggest that δ18Op in the western U.S. is a tracer of condensation height on seasonal timescales. The large influence of condensation height on δ18Op seasonality complicates interpretations of interannual climate proxy records based on isotopes in precipitation as the seasonality is likely not static.

Flowering and Fruiting Patterns in a Subtropical Rain Forest, Taiwan

AbstractReproductive patterns of tropical and temperate plants are usually associated with climatic seasonality, such as rainfall or temperature, and with their phylogeny. It is still unclear, however, whether plant reproductive phenology is influenced by climatic factors and/or phylogeny in aseasonal subtropical regions. The plant reproductive phenology of a subtropical rain forest in northern Taiwan (24°45′ N, 121°35′ E) was monitored at weekly intervals during a 7‐yr period (2002–2009). The flowering patterns of 46 taxa and fruiting patterns of 26 taxa were examined and evaluated in relation to climatic seasonality, phylogenetic constraints, and different phenophases. Our results indicated that most of the studied species reproduced annually. Additionally, both community‐wide flowering and fruiting patterns exhibited distinct annual rhythms and varied little among years. The community flowering peak matched seasonal changes in day length, temperature, and irradiance; while the community fruiting peak coincided with an increase in bird richness and the diet‐switching of resident omnivorous birds. In addition, phylogenetically closely related species tended to reproduce during the same periods of a year. Neither the mean flowering dates nor seasonal variation in solar radiation, however, was related to the fruit development times. Our results indicate the importance of abiotic, biotic, and evolutionary factors in determining the reproductive phenology in this subtropical forest.

Sea levels around Barbados from tide gauges and satellite altimetry

Like many of the small island states of the Caribbean, mean sea level on Barbados was initially established using a short term data set, and this served the purpose of marine navigation. In the 70 years since sea levels were first observed, a number of other measurement series have been made for different purposes. Sea level is now a concern for coastal vulnerability. Data that have been acquired over the years is now brought together with some recent observations to investigate the trend. Discrepancies in the datum that have been used are identified, and further work is undertaken to investigate the cause of variations in sea level that are seen to occur beyond normal tidal and meteorological influence. Satellite altimetry is used with recently acquired data from a tide gauge to show that eddies formed in the Atlantic Ocean can change sea levels around Barbados by up to 0·3 m. Comparative results obtained using tide gauge data and satellite altimetry confirm mean sea level and seasonal variation. Results suggest that integration of these techniques is ideally suited to determining variations in sea level around small island states.

Characterization of ionospheric GPS Total Electron Content (GPS–TEC) in low latitude zone over the Kenyan region during a very low solar activity phase

The ionosphere Total Electron Content (TEC), derived by analyzing dual frequency signals from the Global Positioning System (GPS) recorded from two stations in the Kenyan region is studied. We present the mean diurnal, monthly, seasonal, and annual variation in the ionospheric TEC during the lowest solar activity phase for the periods of 2009–2010. Seasonal variations in daytime TEC show a semiannual periodicity, with minimum in June solstice and maxima in March equinox and December solstice. Using mean hourly monthly TEC, we found semiannual variation with two maxima occurring in months of April–March, and September–October. Seasonal variations in the nighttime TEC reveal semiannual periodicity with high background levels observed in the equinoctial months and low background levels in solstice. Results of seasonal variations and month-to-month variations in TEC have been compared with the TEC derived from the IRI-2007 model using the NeQuick option for the topside electron density. The IRI–TEC is too high for all the seasons except for the March equinox where there seems to be good agreement between observation and model. The model is in good agreement with the monthly variation but overestimates for the months of May, June, July, August and September for all the years studied. The minimum monthly mean is lowest in the model for all the months by about 3–5 TECU in comparison to the GPS–TEC. We attribute this to the fact that the model excludes TEC from the plasmasphere while the overestimation of TEC has been associated to overestimation of the equatorial ion fountain effect and also the inability of the model to predict localized (regional) ionospheric effects arising from electromagnetic forcing at the low latitude.

Sea surface salinity variability during the Indian Ocean Dipole and ENSO events in the tropical Indian Ocean

An ocean reanalysis that covers the period from 1871 to 2008 is used to analyze the interannual variability of sea surface salinity (SSS) in the tropical Indian Ocean. The reanalysis SSS and the SSS anomaly patterns during Indian Ocean Dipole (IOD) and El Niño–Southern Oscillation (ENSO) events are compared with patterns from Argo SSS data. The mean seasonal SSS variation is large in the northern Bay of Bengal compared with variations in the Arabian Sea and equatorial Indian Ocean. During a positive IOD event, positive SSS anomalies are found along the Sumatra coast that are due to the combination of wind‐driven upwelling of subsurface high‐salinity waters, enhanced evaporation, and anomalous surface circulation. The opposite is true, to a lesser extent, during negative IOD events. A dipole mode index for salinity (DMIS) based on SSS data and a new index based on the average of salinity in a region off the coast of Sumatra are introduced to monitor SSS variability during IOD and ENSO events. The impact of concomitant El Niño events on a positive IOD event is large with freshening (a negative SSS anomaly) in the equatorial Indian Ocean and salting (positive SSS anomaly) off the southern Sumatra coast. The (impact of) intense freshening reaches into the southwestern tropical Indian Ocean. The impact of concomitant La Niña with negative IOD is also large with an intense freshening in the southeastern Arabian Sea and salting off the northern Sumatra coast.

Late Pleistocene climatic change in the French Jura (Gigny) recorded in the δ 18O of phosphate from ungulate tooth enamel

Oxygen isotope compositions of phosphate in tooth enamel from large mammals (i.e. horse and red deer) were measured to quantify past mean annual air temperatures and seasonal variations between 145 ka and 33 ka in eastern France. The method is based on interdependent relationships between the δ 18O of apatite phosphate, environmental waters and air temperatures. Horse ( Equus caballus germanicus) and red deer ( Cervus elaphus) remains have δ 18O values that range from 14.2‰ to 17.2‰, indicating mean air temperatures between 7°C and 13°C. Oxygen isotope time series obtained from two of the six horse teeth show a sinusoidal-like signal that could have been forced by temperature variations of seasonal origin. Intra-tooth oxygen isotope variations reveal that at 145 ka, winters were colder (− 7 ± 2°C) than at present (3 ± 1°C) while summer temperatures were similar. Winter temperatures mark a well-developed West–East thermal gradient in France of about − 9°C, much stronger than the −4°C difference recorded presently. Negative winter temperatures were likely responsible for the extent and duration of the snow cover, thus limiting the food resources available for large ungulates with repercussions for Neanderthal predators.

Exploration of the determinants of seasonal Vitamin D

A fundamental assumption when undertaking studies into Vitamin D and populations is that the relative “ranking” of an individual remains constant with respect to time. That is, an individual with the lowest percentile of Vitamin D status in summer will also have the lowest percentile)= of Vitamin D in summer, even though the Vitamin D status may have increased from summer to winter. This work investigates if such relative ranking exists in populations. Most individual‐level epidemiological studies examining vitamin D status in relation to disease risk measure serum 25(OH)D levels at a single time point, statistically “adjusting” for seasonal effects based on the mean seasonal variation in 25(OH)D levels. In longitudinal studies, more than one pre‐existing blood sample may be used, but in comparing either intra‐individually or inter‐individually, adjustment for season is still usually required. The 25(OH)D levels of 60 healthy ambulatory adults (42 female) aged 18 to 87 (median 49) years, in southeast Queensland, Australia (27°S) were tracked from winter to summer. After informed consent, participants were administered a questionnaire surveying past (previous 30 days) sun exposure, timing of sun exposure, sun protection used and dietary Vitamin D intakes. From this collected data, exploration of the determinants of seasonal Vitamin D status was undertaken.

Real-time remote sensing driven river basin modeling using radar altimetry

Abstract. Many river basins have a weak in-situ hydrometeorological monitoring infrastructure. However, water resources practitioners depend on reliable hydrological models for management purposes. Remote sensing (RS) data have been recognized as an alternative to in-situ hydrometeorological data in remote and poorly monitored areas and are increasingly used to force, calibrate, and update hydrological models. In this study, we evaluate the potential of informing a river basin model with real-time radar altimetry measurements over reservoirs. We present a lumped, conceptual, river basin water balance modeling approach based entirely on RS and reanalysis data: precipitation was obtained from the Tropical Rainfall Measuring Mission (TRMM) Multisatellite Precipitation Analysis (TMPA), temperature from the European Centre for Medium-Range Weather Forecast's (ECMWF) Operational Surface Analysis dataset and reference evapotranspiration was derived from temperature data. The Ensemble Kalman Filter was used to assimilate radar altimetry (ERS2 and Envisat) measurements of reservoir water levels. The modeling approach was applied to the Syr Darya River Basin, a snowmelt-dominated basin with large topographical variability, several large reservoirs and scarce hydrometeorological data that is located in Central Asia and shared between 4 countries with conflicting water management interests. The modeling approach was tested over a historical period for which in-situ reservoir water levels were available. Assimilation of radar altimetry data significantly improved the performance of the hydrological model. Without assimilation of radar altimetry data, model performance was limited, probably because of the size and complexity of the model domain, simplifications inherent in model design, and the uncertainty of RS and reanalysis data. Altimetry data assimilation reduced the mean absolute error of the simulated reservoir water levels from 4.7 to 1.9 m, and overall model RMSE from 10.3 m to 6.7 m. Model performance was variable for the different reservoirs in the system. The RMSE ranged from 10% to 76% of the mean seasonal reservoir level variation. Because of its easy accessibility and immediate availability, radar altimetry lends itself to being used in real-time hydrological applications. As an impartial source of information about the hydrological system that can be updated in real time, the modeling approach described here can provide useful medium-term hydrological forecasts to be used in water resources management.

A three-dimensional synthesis inversion of the molecular hydrogen cycle: Sources and sinks budget and implications for the soil uptake

[1] Our understanding of the global budget of atmospheric hydrogen (H2) contains large uncertainties. An atmospheric Bayesian inversion of H2 sources and sinks is presented for the period 1991–2004, based on a two networks of flask measurement stations. The types of fluxes and the spatial scales potentially resolvable by the inversion are first estimated from an analysis of the correlations of errors between the different processes and regions emitting or absorbing H2. Then, the estimated budget of H2 and its uncertainties is presented and discussed, for five groups of fluxes and three groups of large regions, in terms of mean fluxes, seasonal and interannual variations, and long-term trends. One main focus of the study is the improvement of the estimate of H2 soil uptake, which is the largest sink of H2. Various sensitivity tests are performed defining an ensemble of more than 20 inversions. We show that inferring a robust estimate of the H2 soil uptake requires to prescribe the prior magnitude of some other sources and sinks with a small uncertainty. Doing so an estimate of the H2 soil uptake of −62 ± 3 Tg y−1 is inferred for the period 1991–2004 (the uncertainty is the residual error after inversion). The inferred soil H2 sink presents a negative long-term trend that is qualitatively consistent with a bottom-up process-based model.

Solar Activity and Svalbard Temperatures

The long temperature series at Svalbard (Longyearbyen) show large variations and a positive trend since its start in 1912. During this period solar activity has increased, as indicated by shorter solar cycles. The temperature at Svalbard is negatively correlated with the length of the solar cycle. The strongest negative correlation is found with lags 10–12 years. The relations between the length of a solar cycle and the mean temperature in the following cycle are used to model Svalbard annual mean temperature and seasonal temperature variations. Residuals from the annual and winter models show no autocorrelations on the 5 per cent level, which indicates that no additional parameters are needed to explain the temperature variations with 95 per cent significance. These models show that 60 per cent of the annual and winter temperature variations are explained by solar activity. For the spring, summer, and fall temperatures autocorrelations in the residuals exist, and additional variables may contribute to the variations. These models can be applied as forecasting models. We predict an annual mean temperature decrease for Svalbard of °C from solar cycle 23 to solar cycle 24 (2009–20) and a decrease in the winter temperature of °C.

Terdiurnal tide in the extended Canadian Middle Atmospheric Model (CMAM)

We use the extended Canadian Middle Atmosphere Model (CMAM), a general circulation model (GCM), to investigate the nature of the terdiurnal tide. Temperature and horizontal winds from a model run are analyzed to delineate the character of this tide for zonal wave numbers s = −5 to +5. Descriptions of the annual mean amplitudes, seasonal variations, and total tide superposed from the migrating and 10 nonmigrating components are provided. The amplitudes and vertical wavelengths of the various components and the total terdiurnal tide are found to depend strongly on season, latitude, and altitude. The migrating terdiurnal component maximizes at mid and high latitudes with significant amplitudes (annual mean amplitude in wind (temperature) >10 m/s (K)) in the upper mesosphere and lower thermosphere (MLT) region. Between 80 and 100 km, maximum amplitudes occur in winter in both hemispheres, whereas above 100 km, maximum amplitudes occur during solstices. For the zonal wind field, the nonmigrating terdiurnal components Te5, Te3, Te4, Tw4, and Tw5 tend to peak at >50°N/S with amplitudes between 2 and 8 m/s. The other nonmigrating components maximize in the polar regions with amplitudes of 2–10 m/s. Possible generation mechanisms (solar heating and nonlinear interactions) for the migrating terdiurnal tide in the MLT region are also examined. Correlation analysis indicates that nonlinear interactions between the migrating diurnal and semidiurnal tides are unlikely to be the source of the migrating terdiurnal tide.