James Russell

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Papers by James Russell

Ozone quasi-biennial oscillations (QBO), semiannual oscillations (SAO), and correlations with temperature in the mesosphere, lower thermosphere, and stratosphere, based on measurements from SABER on TIMED and MLS on UARS

Journal of Geophysical Research, 2008

The ozone and temperature measurements from Sounding of the Atmosphere using Broadband Emission R... more The ozone and temperature measurements from Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) on the Thermosphere-Ionosphere-Mesosphere-Energetics and Dynamics (TIMED) satellite form a unique set. They provide global information over the range of local solar times, from the lower stratosphere into the lower thermosphere, going back to 2002, by one instrument. On the basis of zonal means of these

Stratospheric and mesospheric temperature variations for the quasi-biennial and semiannual (QBO and SAO) oscillations based on measurements from SABER (TIMED) and MLS (UARS)

Annales Geophysicae, 2006

We present the zonal mean temperature variations for the quasi-biennial oscillation (QBO) and the... more We present the zonal mean temperature variations for the quasi-biennial oscillation (QBO) and the semiannual oscillation (SAO) based on data from SABER on the TIMED spacecraft (years 2002 to 2004) and from MLS on the UARS mission (1992 to 1994). The SABER measurements provide the rare opportunity to analyze data from one instrument over a wide altitude range (15 to

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The use of solid phase extraction columns in fatty acid purification

Organic Geochemistry, 2007

Solid phase extraction (SPE) columns with an aminopropyl bonded stationary phase are commonly use... more Solid phase extraction (SPE) columns with an aminopropyl bonded stationary phase are commonly used to isolate fatty acids. We tested SPE columns with tubes composed of three different materials, high density polyethylene (HDPE), HDPE coated with a fluorinated polymer similar to Teflon Ò (FP-HDPE) and glass, to assess the effects of these products on the purity of fatty acid extracts derived from the different SPE columns. Products made of HDPE released significant levels of short chain (mainly C 16 and C 18 ) fatty acids during elution, while glass and FP-HDPE yielded little contamination. These results urge caution in the use of HDPE products during analysis of short chain fatty acids, especially in applications involving the use of stable isotope ratio values that could be significantly altered by small amounts of contaminants.

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Rwenzori Mountains (Mountains of the Moon): Headwaters of the White Nile

Monographiae Biologicae, 2009

The Rwenzori Mountains, Ptolemy's legendary Mountains of the Moon, were created in the late Plioc... more The Rwenzori Mountains, Ptolemy's legendary Mountains of the Moon, were created in the late Pliocene (less than 5 Ma bp) and stretch along the border between western Uganda and Democratic Republic of Congo. The landscape has been sculptured by repeated growth of glaciers, resulting in numerous lakes and six separate mountains rising over 4,500 m asl. Apart from being considered the (highest) source of the White Nile, the range is also renowned for its high level of endemicity, especially with regard to the terrestrial biota. In this chapter, we sketch the history of exploration, and summarize the main characteristics of Rwenzori's terrestrial and aquatic ecosystems. We also point out some highlights in the paleoclimatic history of the range.

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High-Latitude Gravity Wave Measurements in Noctilucent Clouds and Polar Mesospheric Clouds

Aeronomy of the Earth's Atmosphere and Ionosphere, 2011

Distinct wave forms traditionally observed in Noctilucent Cloud (NLC) photographs and most recent... more Distinct wave forms traditionally observed in Noctilucent Cloud (NLC) photographs and most recently captured in high-resolution panoramic images of Polar Mesospheric Clouds (PMC) provide an exceptionally rich resource for quantifying gravity wave activity and properties in the high-latitude summer mesopause region. Using extensive image data on PMC structures obtained by the Cloud Imaging and Particle Size (CIPS) ultraviolet instrument onboard

TIMED/SABER Observations of the Storm-Time E-Region: Morphology, Chemistry, and Energetics

A new data product derived from TIMED/SABER measurements of 4.3 um limb emission is the NO+(v) vo... more A new data product derived from TIMED/SABER measurements of 4.3 um limb emission is the NO+(v) volume emission rate (VER). We have found NO+(v) VER to be versatile analysis tool for studying the E-region response to solar-geomagnetic storms. Enhancements in nighttime 4.3 um emission during storm periods are due to vibrational excitation of NO+ (i.e., NO+(v)), caused by auroral dosing and subsequent ion-neutral chemical reactions, followed by radiative emission at 4.3 um. The NO+(v) VER is derived by (1) removing the background CO2 infrared emission using SABER observations and non-LTE radiation transfer models, and (2) by performing a standard Abel inversion on the residual radiance. Since NO+ is the terminal E-region ion, the NO+(v) VER is an excellent proxy for characterizing the morphology of the E-region response to magnetic disturbances. Analysis of the April 2002 and Halloween 2003 storm periods reveal spatial structure in the NO+(v) VER that is difficult to understand: large ...

Spatial complexity of 'Little Ice Age' climate in East Africa: sedimentary records from two crater lake basins in western Uganda

The Holocene, 2007

... Palaeolimnological investigations of Lake Naivasha, Kenya (Verschuren et al., 2000), and Lake... more

A Reevaluation of the Ozone Budget with HALOE UARS Data: No Evidence for the Ozone Deficit

Science, 1995

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Climate-Driven Ecosystem Succession in the Sahara: The Past 6000 Years

by James Russell, Dirk Verschuren, and C. Cocquyt

Science, 2008

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Environmental change over the last millennium recorded in two contrasting crater lakes in western Uganda, eastern Africa (Lakes Kasenda and Wandakara)

by James Russell and Angela Lamb

Quaternary Science Reviews, 2011

The last millennium is a key period for understanding environmental change in eastern Africa, as ... more The last millennium is a key period for understanding environmental change in eastern Africa, as there is clear evidence of marked fluctuations in climate (effective moisture) that place modern concern with future climate change in a proper context, both in terms of environmental and societal impacts and responses. Here, we compare sediment records from two small, nearby, closed crater lakes

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The water vapour budget of the stratosphere studied using LIMS and SAMS satellite data

Quarterly Journal of the Royal Meteorological Society, 1986

... A well-known feature of tropical convective systems is the appearance on short time scales (5... more

Troposphere to stratosphere transport at low latitudes as studied using HALOE observations of water vapour 1992-1997

Quarterly Journal of the Royal Meteorological Society, 1998

... A more recent hypoth-esis proposed by Potter and Holton (1995) using model simulations, sugge... more

Glacial forcing of central Indonesian hydroclimate since 60,000 y B.P

by James Russell and Nigel Wattrus

Proceedings of the National Academy of Sciences, 2014

The Indo-Pacific warm pool houses the largest zone of deep atmospheric convection on Earth and pl... more The Indo-Pacific warm pool houses the largest zone of deep atmospheric convection on Earth and plays a critical role in global climate variations. Despite the region&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s importance, changes in Indo-Pacific hydroclimate on orbital timescales remain poorly constrained. Here we present high-resolution geochemical records of surface runoff and vegetation from sediment cores from Lake Towuti, on the island of Sulawesi in central Indonesia, that continuously span the past 60,000 y. We show that wet conditions and rainforest ecosystems on Sulawesi present during marine isotope stage 3 (MIS3) and the Holocene were interrupted by severe drying between ∼33,000 and 16,000 y B.P. when Northern Hemisphere ice sheets expanded and global temperatures cooled. Our record reveals little direct influence of precessional orbital forcing on regional climate, and the similarity between MIS3 and Holocene climates observed in Lake Towuti suggests that exposure of the Sunda Shelf has a weaker influence on regional hydroclimate and terrestrial ecosystems than suggested previously. We infer that hydrological variability in this part of Indonesia varies strongly in response to high-latitude climate forcing, likely through reorganizations of the monsoons and the position of the intertropical convergence zone. These findings suggest an important role for the tropical western Pacific in amplifying glacial-interglacial climate variability.

Palaeolimnological evidence for widespread late 18th century drought across equatorial East Africa

by James Russell and Dirk Verschuren

Palaeogeography, Palaeoclimatology, Palaeoecology, 2008

The sediment records of three shallow climate-sensitive lakes in equatorial East Africa (Chibwera... more The sediment records of three shallow climate-sensitive lakes in equatorial East Africa (Chibwera and Kanyamukali in western Uganda, and Baringo in central Kenya) contain clear lithological evidence of an episode of complete desiccation in the relatively recent past. Quantitative stratigraphic analyses of bulk sediment composition, texture (% sand and coarse organic detritus), the C/N ratio of bulk organic matter, and magnetic susceptibility allowed us to define a common succession of sedimentary units in all three lakes. This common stratigraphy includes a basal unit of dry and stiff low-organic clays capped by a horizon of peaty mud or peat, overlain by organic lake sediment. We interpret this stratigraphy to represent an episode of (nearly) complete desiccation of these lake basins. This was followed first by an early phase of modest lake refilling, during which time extensive littoral and submerged vegetation developed, producing peaty lake deposits. Mostly higher lake levels later on resulted in deposition of fine-grained lake muds. Using 210 Pb and 137 Cs activity profiles combined with four AMS 14 C dates on single terrestrial plant macrofossils or multiple charred grass particles indicate that in all three lakes the episode of most recent complete desiccation occurred in the late 18th and early 19th century. These results add to an accumulating body of palaeoenvironmental data revealing a prolonged period of extreme drought in equatorial East Africa about 200 years ago, also documented in the cultural history of the African Great Lakes region. Given the geographical spread of the study lakes across the East African plateau, these results indicate that the climatic anomaly of reduced rainfall responsible for this drought was at least sub-continental in scale.

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Half-precessional dynamics of monsoon rainfall near the East African Equator

by Raymond Bradley and James Russell

Nature, 2009

External climate forcings-such as long-term changes in solar insolation-generate different climat... more External climate forcings-such as long-term changes in solar insolation-generate different climate responses in tropical and high latitude regions 1 . Documenting the spatial and temporal variability of past climates is therefore critical for understanding how such forcings are translated into regional climate variability. In contrast to the data-rich middle and high latitudes, high-quality climate-proxy records from equatorial regions are relatively few 2-4 , especially from regions experiencing the bimodal seasonal rainfall distribution associated with twice-annual passage of the Intertropical Convergence Zone. Here we present a continuous and well-resolved climate-proxy record of hydrological variability during the past 25,000 years from equatorial East Africa. Our results, based on complementary evidence from seismic-reflection stratigraphy and organic biomarker molecules in the sediment record of Lake Challa near Mount Kilimanjaro, reveal that monsoon rainfall in this region varied at half-precessional ( 11,500-year) intervals in phase with orbitally controlled insolation forcing. The southeasterly and northeasterly monsoons that advect moisture from the western Indian Ocean were strengthened in alternation when the inter-hemispheric insolation gradient was at a maximum; dry conditions prevailed when neither monsoon was intensifiedand modestlocalMarch orSeptemberinsolation weakened the rain season that followed. On sub-millennial timescales, the temporal pattern of hydrological change on the East African Equator bears clear high-northern-latitude signatures, but on the orbital timescale it mainly responded to low-latitude insolation forcing. Predominance of low-latitude climate processes in this monsoon region can be attributedtothelow-latitudepositionofitscontinentalregionsofsurfaceair flow convergence, and its relative isolation from the Atlantic Ocean, where prominent meridional overturning circulation more tightly couples low-latitude climate regimes to high-latitude boundary conditions.

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Satellite confirmation of the dominance of chlorofluorocarbons in the global stratospheric chlorine budget

Nature, 1996

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Seasonal Cycles and QBO Variations in Stratospheric CH 4 and H 2 O Observed in UARS HALOE Data

Journal of the Atmospheric Sciences, 1998

Measurements of stratospheric methane (CH 4 ) and water vapor (H 2 O) are used to investigate sea... more Measurements of stratospheric methane (CH 4 ) and water vapor (H 2 O) are used to investigate seasonal and interannual variability in stratospheric transport. Data are from the Halogen Occultation Experiment (HALOE) on the Upper Atmosphere Research Satellite (UARS) spanning 1991-97. Profile measurements are binned according to analyzed potential vorticity fields (equivalent latitude mapping), and seasonal cycles are fit using harmonic regression analysis. Methane data from the UARS Cryogenic Limb Array Etalon Spectrometer and water vapor from the Microwave Limb Sounder are also used to fill in winter polar latitudes (where HALOE measurements are unavailable), yielding complete global seasonal cycles. These data reveal well-known seasonal variations with novel detail, including 1) the presence of enhanced latitudinal gradients (mixing barriers) in the subtropics and across the polar vortices, 2) strong descent inside the polar vortices during winter and spring, and 3) vigorous seasonality in the tropical upper stratosphere, related to seasonal upwelling and the semiannual oscillation. The observed variations are in agreement with aspects of the mean meridional circulation derived from stratospheric meteorological analyses. Interannual variations are also investigated, and a majority of the variance is found to be coherent with the equatorial quasibiennial oscillation (QBO). Strong QBO influence is found in the tropical upper stratosphere: the double-peaked ''rabbit ears'' structure occurs primarily during QBO westerlies. The QBO also modulates the latitudinal position of the tropical ''reservoir'' in the middle stratosphere.

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Spring Dehydration in the Antarctic Stratospheric Vortex Observed by HALOE

Journal of the Atmospheric Sciences, 1994

The distribution of dehydrated air in the middle and lower stratosphere during the 1992 Southern ... more The distribution of dehydrated air in the middle and lower stratosphere during the 1992 Southern Hemisphere spring is investigated using Halogen Occultation Experiment (HALOE) observations and trajectory techniques. Comparisons between previously published Version 9 and the improved Version 16 retrievals on the 700-K isentropic surface show very slight (0.05 ppmv) increases in Version 16 CH4 relative to Version 9 within

Paleolimnological records of recent glacier recession in the Rwenzori Mountains, Uganda-D. R. Congo

Journal of Paleolimnology, 2009

The status of tropical glaciers is enormously important to our understanding of past, present, an... more The status of tropical glaciers is enormously important to our understanding of past, present, and future climate change, yet lack of continuous quantitative records of alpine glacier extent on the highest mountains of tropical East Africa prior to the 20th century has left the timing and drivers of recent glacier recession in the region equivocal. Here we investigate recent changes (the last 150-700 years) in lacustrine sedimentation, glacier extent, and biogeochemical processes in the Rwenzori Mountains (Uganda-Democratic Republic of Congo) by comparing sedimentological (organic and siliciclastic component determined by loss-onignition; LOI) and organic geochemical profiles (carbon and nitrogen abundance, ratio, and isotopic composition of sedimentary organic matter) from lakes occupying presently glaciated catchments against similar profiles from lakes located in catchments lacking glaciers. The siliciclastic content of sediments in the 'glacial lakes' significantly decreases towards the present, whereas 'non-glacial lakes' generally show weak trends in their siliciclastic content over time, demonstrating that changes in the siliciclastic content of glacial lake sediments primarily record fluctuations in glacier extent. Radiometric dating of our sediment cores indicates that prior to their late 19th-century recession Rwenzori glaciers stood at expanded 'Little Ice Age' positions for several centuries under a regionally dry climate regime, and that recession was underway by 1870 AD, during a regionally wet episode. These findings suggest that the influence of late 19th century reductions in precipitation in triggering Rwenzori glacier recession is weaker than previously thought. Our organic geochemical data indicate that glacier retreat has significantly affected carbon cycling in Afroalpine lakes, but trends in aquatic ecosystem functioning are variable among lakes and require more detailed analysis.

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Paleotemperature reconstruction in tropical Africa using fossil Chironomidae (Insecta: Diptera)

by James Russell and Dirk Verschuren

Journal of Paleolimnology, 2010

Fossil assemblages of chironomid larvae (non-biting midges) preserved in lake sediments are well-... more Fossil assemblages of chironomid larvae (non-biting midges) preserved in lake sediments are well-established paleothermometers in north-temperate and boreal regions, but their potential for temperature reconstruction in tropical regions has never before been assessed. In this study, we surveyed sub-fossil chironomid assemblages in the surface sediments of 65 lakes and permanent pools in southwestern Uganda (including the Rwenzori Mountains) and central

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