bluuebunny/crossref_metadata_2025 huggingface dataset:
Parallel Phosphatidylinositol-3 Kinase and p42/44 Mitogen-Activated Protein Kinase Signaling Pathways Subserve the Mitogenic and Antiapoptotic Actions of Insulin-Like Growth Factor I in Osteoblastic Cells
Authors: Grey Andrew , Chen Qi , Xu Xin , Callon Karen , Cornish Jill
Published: July 2003

IGF-I is an endocrine and paracrine regulator of skeletal homeostasis, principally by virtue of its anabolic effects on osteoblastic cells. In the current study, we examined the intracellular signaling pathways by which IGF-I promotes proliferation and survival in SaOS-2 human osteoblastic cells. Inhibition of each of the phosphatidylinositol-3 kinase (PI-3 kinase), p42/44 MAPK, and p70s6 kinase pathways partially inhibited the ability of IGF-I to stimulate osteoblast proliferation and survival. Because activation of p70s6 kinase is downstream of both PI-3 kinase and p42/44 MAPK activation in osteoblasts treated with IGF-I, this ribosomal kinase represents a convergence point for IGF-I-induced PI-3 kinase and p42/44 MAPK signaling in osteoblastic cells. In addition, abrogation of PI-3 kinase-dependent Akt signaling, which does not inhibit IGF-I-induced p70s6 kinase phosphorylation, also inhibited the antiapoptotic effects of IGF-I in osteoblasts. Finally, interruption of Gβγ signaling partially abrogated the ability of IGF-I to promote osteoblast survival, without inhibiting signaling through PI-3 kinase/Akt, p42/44 MAPKs, or p70s6 kinase. These data suggest that IGF-I signals osteoblast mitogenesis and survival through parallel, partly overlapping intracellular pathways involving PI-3 kinase, p42/44 MAPKs, and Gβγ subunits.
Inhibition of Oxytocin Receptor and Estrogen Receptor-α Expression, But Not Relaxin Receptors (LGR7), in the Myometrium of Late Pregnant Relaxin Gene Knockout Mice
Authors: Siebel Andrew L. , Gehring Helen M. , Reytomas Irna Grace T. , Parry Laura J.
Published: July 2003

This study used relaxin (RLX) gene knockout mice (Rlx−/−) to investigate the effects of RLX on myometrial oxytocin receptor (OTR) and estrogen receptor (ER)-α gene expression in late gestation. We also characterized the temporal expression of the RLX receptor (LGR7) and demonstrated gene transcripts in the myometrium of Rlx+/+ and Rlx−/− mice. There was a significant (P < 0.05) decrease in myometrial LGR7 gene expression on d 17.5 and 18.5 post coitum (pc) compared with earlier stages of gestation, but no differences between Rlx+/+ and Rlx−/− mice. Myometrial OTR mRNA levels increased at the end of gestation in Rlx+/+ but not Rlx−/− mice. ERα gene expression was up-regulated on d 14.5 pc in Rlx+/+ mice, with mRNA levels remaining high throughout late gestation. In contrast, ERα mRNA levels were significantly lower in Rlx−/− mice on d 14.5 and 18.5 pc. These data show that the increases in myometrial OTR and ERα expression in late pregnant Rlx+/+ mice were attenuated in Rlx−/− mice. The effects of RLX on OTRs are probably mediated via activation of ERα. Finally, RLX receptor expression in the myometrium of Rlx−/− mice did not differ from wild-type mice, implying that RLX does not influence expression of its receptor.
Dual Regulation of Proliferation and Growth Arrest in Prostatic Stromal Cells by Transforming Growth Factor-β1
Authors: Zhou Wei , Park Irwin , Pins Michael , Kozlowski James M. , Jovanovic Borko , Zhang Ju , Lee Chung , Ilio Kenneth
Published: July 2003

In a preliminary study, we observed that TGF-β1 induced both proliferation and growth arrest in prostatic stromal cells, depending on the concentration of TGF-β1 used in the culture medium. In this study, we explored possible mechanisms of this dual effect of TGF-β. Primary cultures of prostatic stromal cells, established from clinical surgical specimens and treated with low doses of TGF-β1 (0.001–0.01 ng/ml), resulted in an increase in cell proliferation. The addition of neutralizing antibody against platelet-derived growth factor (PDGF)-BB, but not anti-PDGF-AA, abrogated this stimulatory effect of TGF-β1. TGF-β1 treatment resulted in a dose-related increase in PDGF-BB production as measured by ELISA. Cells underwent growth arrest at high concentrations of TGF-β1 (1.0 and 10 ng/ml). An inhibitor of cyclin-dependent kinase (cdk), p15INK4b, was up-regulated at both transcript and protein levels in these cultures by TGF-β1 in a dose-related manner as determined by RT-PCR and Western blot analysis. The transcript, but not the protein, for another cdk inhibitor, p21Cip1, was up-regulated with treatment of TGF-β1 to these cells. Levels of other cdk inhibitors, such as p16INK4a and p27Kip1, were constitutively expressed in prostatic stromal cells and were not significantly affected by TGF-β1 treatment. Finally, the growth arrest effect of TGF-β1 was abrogated when antisense oligonucleotides to p15INH4b, but not p21Cip1, were added to the culture medium. These data indicate that the dual effect of TGF-β1 is mediated, at least, by up-regulation of PDGF-BB and p15INK4b, respectively.
Na+/H+ Exchanger-Regulatory Factor 1 Mediates Inhibition of Phosphate Transport by Parathyroid Hormone and Second Messengers by Acting at Multiple Sites in Opossum Kidney Cells
Authors: Mahon Matthew J. , Cole Judith A. , Lederer Eleanor D. , Segre Gino V.
Published: July 2003

The opossum kidney (OK) line displays PTH-mediated activation of adenylyl cyclase and phospholipase C and inhibition of phosphate (Pi) uptake via regulation of the type IIa sodium-phosphate cotransporter, consistent with effects in vivo. OKH cells, a subclone of the OK cell line, robustly activates PTH-mediated activation of adenylyl cyclase, but is defective in PTH-mediated inhibition of sodium-phosphate cotransport and signaling via phospholipase C. Compared with wild-type OK cells, OKH cells express low levels of the Na+/H+ exchanger regulatory factor 1 (NHERF-1). Stable expression of NHERF-1 in OKH cells (OKH-N1) rescues the PTH-mediated inhibition of sodium-phosphate cotransport. NHERF-1 also restores the capacity of 8-bromo-cAMP and forskolin to inhibit Pi uptake, but the PTH dose-response for cAMP accumulation and inhibition of Pi uptake differ by 2 orders of magnitude. NHERF-1, in addition, modestly restores phorbol ester-mediated inhibition of Pi uptake, which is much weaker than that elicited by PTH. A poor correlation exists between the inhibition of Pi uptake mediated by PTH (∼60%) and the inhibition mediated by phorbol 12-myristate 13-acetate (∼30%) and the ability of these molecules to activate the protein kinase C-responsive reporter gene. Furthermore, we show that NHERF-1 directly interacts with type IIa cotransporter in OK cells. Although, PTH-mediated inhibition of Pi uptake in OK cells is largely NHERF-1 dependent, the signaling pathway(s) by which this occurs is still unclear. These pathways may involve cooperativity between cAMP- and protein kinase C-dependent pathways or activation/inhibition of an unrecognized NHERF-1-dependent pathway(s).
Sphingosine Kinase Transmits Estrogen Signaling in Human Breast Cancer Cells
Authors: Sukocheva Olga A. , Wang Lijun , Albanese Nathaniel , Pitson Stuart M. , Vadas Mathew A. , Xia Pu
Published: July 2003

Current understanding of cytoplasmic signaling pathways that mediate estrogen action in human breast cancer is incomplete. Here we report that treatment with 17β-estradiol (E2) activates a novel signaling pathway via activation of sphingosine kinase (SphK) in MCF-7 breast cancer cells. We found that E2 has dual actions to stimulate SphK activity, i.e. a rapid and transient activation mediated by putative membrane G protein-coupled estrogen receptors (ER) and a delayed but prolonged activation relying on the transcriptional activity of ER. The E2-induced SphK activity consequently activates downstream signal cascades including intracellular Ca2+ mobilization and Erk1/2 activation. Enforced expression of human SphK type 1 gene in MCF-7 cells resulted in increases in SphK activity and cell growth. Moreover, the E2-dependent mitogenesis were highly promoted by SphK overexpression as determined by colony growth in soft agar and solid focus formation. In contrast, expression of SphKG82D, a dominant-negative mutant SphK, profoundly inhibited the E2-mediated Ca2+ mobilization, Erk1/2 activity and neoplastic cell growth. Thus, our data suggest that SphK activation is an important cytoplasmic signaling to transduce estrogen-dependent mitogenic and carcinogenic action in human breast cancer cells.
Transcriptional Profiling of the Chick Pineal Gland, a Photoreceptive Circadian Oscillator and Pacemaker
Authors: Bailey Michael J. , Beremand Phillip D. , Hammer Rick , Bell-Pedersen Deborah , Thomas Terry L. , Cassone Vincent M.
Published: July 2003

The avian pineal gland contains both circadian oscillators and photoreceptors to produce rhythms in biosynthesis of the hormone melatonin in vivo and in vitro. The molecular mechanisms for melatonin biosynthesis are largely understood, but the mechanisms driving the rhythm itself or the photoreceptive processes that entrain the rhythm are unknown. We have produced cDNA microarrays of pineal gland transcripts under light-dark and constant darkness conditions. Rhythmic transcripts were classified according to function, representing diverse functional groups, including phototransduction pathways, transcription/translation factors, ion channel proteins, cell signaling molecules, and immune function genes. These were also organized relative to time of day mRNA abundance in light-dark and constant darkness. The transcriptional profile of the chick pineal gland reveals a more complex form of gene regulation than one might expect from a gland whose sole apparent function is the rhythmic biosynthesis of melatonin. The mRNAs encoding melatonin biosynthesis are rhythmic as are many orthologs of mammalian “clock genes.” However, the oscillation of phototransductive, immune, stress response, hormone binding, and other important processes in the transcriptome of the pineal gland, raises new questions regarding the role of the pineal gland in circadian rhythm generation, organization, and avian physiology.
The Spectrum and Term System of S VII
Authors: Christer Jupén  , Lars Engström
Published: July 2003

The spectrum of six times ionized sulphur, S VII, has been investigated in the wavelength region 200–4000 Å by means of the beam-foil and laser-produced plasma techniques. The analysis comprises 219 lines of which 105 are newly identified. The present work establishes 123 2s22p5nlenergy levels of which 66 are new. The level energies are determined with an internal consistency of better than 20 cm-1. The observed level structure has been investigated by means of parametric calculations. The center-of-gravity ionization energy of the 2s22p52P limit has been determined to 2 269 410±60 cm-1. Of the identified 3s-3p and 3p-3d lines 27 are present in the solar coronal spectrum recorded by the SUMER instrument onboard the SOHO satellite. The present work adds 2 new solar identifications and improved wavelengths of some other solar coronal lines.
Rat aorta-derived mural precursor cells express the Tie2 receptor and respond directly to stimulation by angiopoietins
Authors: Iurlaro Monica , Scatena Marta , Zhu Wen-Hui , Fogel Eric , Wieting Susan L. , Nicosia Roberto F.
Published: July 2003

Recent studies have implicated the Tie2 tyrosine-kinase receptor and its main ligands - angiopoietin-1 (Ang-1) and angiopoietin-2 (Ang-2) - as crucial regulators of mural cell recruitment during angiogenesis. Angiopoietin-mediated activation of Tie2 promotes perivascular mural cell assembly, but the mechanisms regulating this process are poorly understood because differentiated mural cells do not have the Tie2 receptor, which is reportedly expressed only in endothelial cells. There is also no direct evidence that Tie2 activation results in production of mural cell chemoattractants by the endothelium. In the rat aorta model of angiogenesis,developing microvessels recruit mural cells from the intimal/subintimal layers of the aortic wall. Ang-1 and Ang-2 promote angiogenesis in this system,stimulating branching morphogenesis and mural cell assembly. Mural precursor cells (MPCs) isolated with a nonenzymatic method from the intimal aspect of the rat aorta were positive for smooth muscle cell markers (α-smooth muscle actin and calponin) and negative for endothelial markers(factor-VIII-related antigen and CD31). These cells responded chemotactically to Ang-1 and Ang-2, and secreted MMP-2 when treated with these factors. Western-blot analysis, immunocytochemistry and RT-PCR demonstrated that MPCs express the Tie2 receptor. Immunoprecipitation showed phosphorylation of MPC Tie2 on tyrosine residues upon stimulation with Ang-1 or Ang-2. Surface expression of Tie2 was further demonstrated by isolating Tie2+/α-smooth muscle actin+ MPCs from primary aortic outgrowths with anti-Tie2-IgG-coated magnetic beads. Immunostaining of the rat aorta confirmed expression of Tie2 not only in endothelial cells but also in nonendothelial mesenchymal cells located in the aortic intimal/subintimal layers, which are the source of MPCs. These data indicate that the aortic wall contains Tie2+ nonendothelial mesenchymal cells and suggest that Tie2-related recruitment of mural cells during angiogenesis may occur through angiopoietin-mediated direct stimulation of these cells.
Endothelial inflammation: the role of differential expression of N-deacetylase/N-sulphotransferase enzymes in alteration of the immunological properties of heparan sulphate
Authors: Carter Noel M. , Ali Simi , Kirby John A.
Published: July 2003

Heparan sulphate N-deacetylase/N-sulphotransferase (NDST) enzymes catalyse the reaction that initiates sulphation and subsequent modification of the oligosaccharide, heparan sulphate (HS). The extent and distribution of sulphate substitution on HS plays a vital role in regulation of the binding of a range of proteins, including IFN-γ, several interleukins and most chemokines. In this study, the expression of NDST transcripts was found to be non-uniform between a range of cell types, suggesting that different cells produce characteristic HS species. It was found that stimulation of the HMEC-1 microvascular endothelial cell line with the pro-inflammatory cytokines IFN-γ and TNF-α caused a transient decrease in the level of NDST-1 and -2 transcripts after 4 hours (P<0.05 and P<0.01 respectively), but the expression of NDST-1 increased above control levels after 16 hours (P<0.01). The change in NDST expression was concurrent with an increase in the abundance of sulphated HS epitopes on the cell surface; this was not caused by variation in the expression of proteoglycans or by changes in the rate of GAG turnover. Cytokine-stimulated endothelial cells also showed an increase in their potential to bind RANTES(CCL5); this was abrogated by chlorate blockade of sulphotransferase activity or by heparitinase cleavage of cell surface HS. Monolayers of cytokine-stimulated HMEC-1 also supported an enhanced leukocyte chemotactic response towards RANTES. This study demonstrated that pro-inflammatory cytokines can increase NDST expression leading to increased sulphation of HS and a corresponding increase in sequestration of functional RANTES at the apical surface of endothelial cells. This may enhance leukocyte extravasation at sites of inflammation.
Inhibition of GTP-dependent vesicle trafficking impairs internalization of plasmalemmal eNOS and cellular nitric oxide production
Authors: Chatterjee Suvro , Cao Sheng , Peterson Timothy E. , Simari Robert D. , Shah Vijay
Published: July 2003

The Ca2+ mobilizing peptide, bradykinin (BK), stimulates endothelial nitric oxide synthase (eNOS)-derived cellular nitric oxide (NO)production in association with altering the subcellular distribution of the enzyme. In the present study we examine the influence of cellular GTPases,particularly the large GTPase dynamin, on BK-mediated eNOS localization and cellular NO production. BK stimulation of ECV cells, which were stably transfected with eNOS-GFP (eNOS-GFP ECV304), increased NO production. This was associated with the mobilization of eNOS-GFP protein into Triton X-100-insoluble fractions of cell lysates, and an internalization of plasmalemmal eNOS-GFP in live and fixed ECV 304 cells. Incubation of digitonin-permeabilized ECV304 cells with the non-hydrolyzed GTP analog,GTP-γ-S, abrogated the BK-mediated internalization of eNOS-GFP as assessed by confocal microscopy. Conversely, inhibition of clathrin-dependent endocytosis, via overexpression of AP 180 or pretreatment of cells with chlorpromazine, did not influence BK-mediated eNOS redistribution. Furthermore, specific inhibition of dynamin-2 GTPase function by overexpression of a dominant negative construct, K44A, prevented the BK-mediated enrichment of eNOS-GFP within low buoyant density,caveolin-enriched fractions of eNOS-GFP ECV304 cell lysates. Dynamin-2 K44A overexpression also markedly impaired BK-dependent, L-NAME-inhibited NO production as did incubation of permeabilized cells with GTP-γ-s. These studies demonstrate that disruption of dynamin- and GTP-dependent, but clathrin-independent, vesicle trafficking pathways impairs BK-dependent cellular NO production, via inhibition of the internalization of eNOS-containing plasmalemmal vesicles.
Novel PI 3-kinase-dependent mechanisms of trypanosome invasion and vacuole maturation
Authors: Woolsey Aaron M. , Sunwoo Lisa , Petersen Christine A. , Brachmann Saskia M. , Cantley Lewis C. , Burleigh Barbara A.
Published: July 2003

Mammalian cell invasion by the protozoan parasite, Trypanosoma cruzi, is facilitated by the activation of host cell phosphatidylinositol 3 (PI 3)-kinases. We demonstrate that the well-characterized Ca2+-regulated lysosome-mediated parasite entry pathway is abolished by wortmannin pretreatment. In addition, we have characterized a novel route of T. cruzi invasion unexpectedly revealed in the course of this study. For over a decade, targeted exocytosis of lysosomes at the host cell plasma membrane was considered as the primary mechanism for T. cruzi entry into non-professional phagocytic cells. We now provide evidence that a significant fraction (50% or greater) of invading T. cruzi trypomastigotes exploit an alternate actin-independent entry pathway that involves formation of a tightly associated host cell plasma membrane-derived vacuole enriched in the lipid products of class I PI 3-kinases, PtdInsP3/PtdIns(3,4)P2. Initially devoid of lysosomal markers, the resultant parasite-containing vacuoles gradually acquire lysosome associated membrane protein 1 (lamp-1) and fluid phase endocytic tracer from the lysosomal compartment. In striking contrast to latex bead phagosomes, few T. cruzi vacuoles associate with the early endosomal marker, EEA1 and the 'maturation' process becomes refractory to PI 3-kinase inhibition immediately following parasite internalization. Jointly, these data provide a new paradigm for T. cruzi invasion of non-professional phagocytic cells and reveal a novel vacuole maturation process that appears to bypass the requirement for EEA1.
Activity, phosphorylation state and subcellular distribution of GLUT4-targeted Akt2 in rat adipose cells
Authors: Chen Xiaoli , Al-Hasani Hadi , Olausson Torbjorn , Wenthzel Ann-Marie , Smith Ulf , Cushman Samuel W.
Published: July 2003

In this study, fusion of the kinase domain of Akt2 to the cytosolic C terminus of exofacially-HA-tagged GLUT4 is used to investigate the activity,phosphorylation state and subcellular localization of Akt2 specifically targeted to the GLUT4-trafficking pathway in rat adipose cells. Fusion of wild-type (wt) Akt2, but not a kinase-dead (KD) mutant results in constitutive targeting of the HA-GLUT4 fusion protein to the cell surface to a level similar to that of HA-GLUT4 itself in the insulin-stimulated state. Insulin does not further enhance the cell-surface level of HA-GLUT4-Akt2-wt, but does stimulate the translocation of HA-GLUT4-Akt2-KD. Cell-surface HA-GLUT4-Akt2-wt is found to be phosphorylated on Ser474 in both the absence and presence of insulin, and mutation of Ser474 to Ala reduces the increased basal cell-surface localization of the fusion protein. While Ser474 phosphorylation of HA-GLUT4-Akt2-KD is detected only in the insulin-stimulated state, trapping this fusion protein on the cell surface by coexpression of a dominant negative mutant dynamin does not induce Ser474 phosphorylation. Phosphorylation on Thr309 is not detectable in either HA-GLUT4-Akt2-wt or HA-GLUT4-Akt2-KD, in either the basal or insulin-stimulated state, and mutation of Thr309 to Ala does not influence the insulin-independent increases in cell-surface localization and Ser474 phosphorylation. Expression of HA-GLUT4-Akt2-wt stimulates the translocation of cotransfected myc-GLUT4 to a level similar to that in the insulin-stimulated state; this increase is moderately reduced by mutation of Ser474 to Ala and absent with the kinase-dead mutant. These results demonstrate that targeting Akt2 to the GLUT4-trafficking pathway induces Akt2 activation and GLUT4 translocation. Ser474 phosphorylation is an autocatalytic reaction requiring an active kinase, and kinase activity is associated with a plasma membrane localization. Fusion of Akt2 to the C terminus of GLUT4 appears to substitute for Thr309 phosphorylation in activating the autocatalytic process.
An essential role of Rab5 in uniformity of synaptic vesicle size
Authors: Shimizu Hideyuki , Kawamura Satoru , Ozaki Koichi
Published: July 2003

Rab5 small GTPase is a famous regulator of endocytic vesicular transport from plasma membrane to early endosomes. In neurons, Rab5 is found not only on endocytic vesicles in cell bodies but also on synaptic vesicles in nerve terminals. However, the function of Rab5 on synaptic vesicles remains unclear. Here, we elucidate the function of Rab5 on synaptic vesicles with in vivo and in vitro experiments using Drosophila photoreceptor cells. Functional inhibition of Rab5 with Rab5N142I, a dominant negative version of Drosophila Rab5, induced enlargement of synaptic vesicles. This enlargement was, however, suppressed by enhancing synaptic vesicle recycling under light illumination. In addition, synaptic vesicles prepared from Rab5N142I-expressing flies exhibited homotypic fusion in vitro. These results indicate that Rab5 functions to keep the size of synaptic vesicles uniform by preventing their homotypic fusion. By contrast, Rab5 was not involved in the endocytic reformation of synaptic vesicles, contrary to expectation from its conventional function. Furthermore, we electrophysiologically and behaviourally showed that the function of Rab5 is essential for efficient signal transmission across synapses.
Pex10p links the ubiquitin conjugating enzyme Pex4p to the protein import machinery of the peroxisome
Authors: Eckert Jörg H. , Johnsson Nils
Published: July 2003

The protein import machinery of the peroxisome consists of many proteins,collectively called the peroxins. By applying the split-ubiquitin technique we systematically tested the pair-wise interactions between the Nub-and Cub-labeled peroxins for the first time in the living cells of the yeast Saccharomyces cerevisiae. We found that Pex10p plays a central role in the protein interaction network by connecting the ubiquitin conjugation enzyme Pex4p to the other members of the protein import machinery. A yeast strain harboring a deletion of PEX3 enabled us to estimate the influence of the peroxisomal membrane on the formation of a subset of the investigated protein-protein interactions.
VE-cadherin simultaneously stimulates and inhibits cell proliferation by altering cytoskeletal structure and tension
Authors: Nelson Celeste M. , Chen Christopher S.
Published: July 2003

Engagement of vascular endothelial (VE)-cadherin leads to the cessation of proliferation commonly known as 'contact inhibition'. We show that VE-cadherin inhibits growth by mediating changes in cell adhesion to the extracellular matrix. Increasing cell-cell contact decreased cell spreading and proliferation, which was reversed by blocking engagement of VE-cadherin. Using a new system to prevent the cadherin-induced changes in cell spreading, we revealed that VE-cadherin paradoxically increased proliferation. Treating cells with inhibitors of PKC and MEK abrogated the stimulatory signal at concentrations that disrupted the formation of actin fibers across the cell-cell contact. Directly disrupting actin fibers, blocking actin-myosin-generated tension, or inhibiting signaling through Rho specifically inhibited the cadherin-induced proliferative signal. By progressively altering the degree to which cell-cell contact inhibited cell spreading, we show that cell-cell contact ultimately increased or decreased the overall proliferation rate of the population by differentially shifting the balance between the two opposing proliferative cues. The existence of opposing growth signals induced by VE-cadherin that are both mediated through crosstalk with cytoskeletal structure highlights the complex interplay of mechanical and chemical signals with which cells navigate in their physical microenvironment.
Tropospheric–stratospheric coupling: Extratropical synoptic systems in the lower stratosphere
Authors: Canziani Pablo O. , Legnani Walter E.
Published: July 2003

Synoptic‐scale disturbances, existing in the lower stratosphere of middle to high southern latitudes and linked to tropospheric synoptic systems, are reviewed. Geopotential and wind fields show that synoptic‐scale perturbations exist in the re‐analysis products of the US National Center for Environmental Prediction, at least up to the 50 hPa level. A spatial spectral approach is used to demonstrate the existence of sizeable, episodic synoptic‐scale perturbations throughout the lower stratosphere. The extension of synoptic systems from the troposphere into the lower stratosphere at high and mid latitudes, during early spring is discussed, using two case‐studies. The background conditions given by the mean zonal flow, modulated by planetary‐scale waves, appear to provide the limiting conditions for such penetration, which would have been theoretically impossible if the zonal mean flow alone were considered. The results are discussed under a simple generalization of the Charney–Drazin limits to wave propagation. Copyright © 2003 Royal Meteorological Society.
A probabilistic description of convective mass fluxes and its relationship to extreme‐value theory
Authors: Naveau P. , Moncrieff M. W.
Published: July 2003

The vertical flux of mass by atmospheric convection, and convective cloud systems in particular, is a key quantity used in parametrization schemes for numerical weather‐prediction models and climate models. The concept of formulating mass fluxes in terms of statistical quantities is discussed and a probabilistic description of the upward mass fluxes, based on extreme‐value theory, is presented. This approach is illustrated by a statistical analysis of two‐dimensional, numerical realizations of two regimes of tropical convection, namely squall lines and non‐squall clusters. Our statistical model allows these distinct cloud systems, which play a key role in determining the shape of the mass‐flux profile, to be efficiently integrated. Also taken into account is the distinction between mesoscale and convective components of the mass flux. Copyright © 2003 Royal Meteorological Society.
Nonlinear singular spectrum analysis of the tropical stratospheric wind
Authors: Hsieh William W. , Hamilton Kevin
Published: July 2003

The neural‐network‐based nonlinear singular spectrum analysis (NLSSA) is applied to the zonal winds in the 70–10 hPa region (roughly 20–30 km altitude) measured at near‐equatorial stations during 1956–2000. The data are pre‐filtered by the linear singular spectrum analysis (SSA), with the leading eight SSA principal components (PCs) used as inputs for the NLSSA. The NLSSA fits a curve to the data in the eight‐dimensional PC space. This NLSSA curve, when projected onto the two‐dimensional plane spanned by any two PCs, shows the relation between the two SSA PCs. As different SSA modes are associated with different time‐scales, the relations found by the NLSSA reveal the time‐scales between which there are interactions—interactions between the dominant quasi‐biennial oscillation (QBO) time‐scale of about 28 months and the first harmonic at 14 months, and between 28 months and 12 months are found. The anharmonic nature of the QBO is well represented by the NLSSA mode 1, but not by individual SSA modes. The NLSSA is also applied to the time series of the zonal‐wind acceleration. Copyright © 2003 Royal Meteorological Society.
A feedback mechanism between soil‐moisture distribution and storm tracks
Authors: Pal Jeremy S. , Eltahir Elfatih A. B.
Published: July 2003

How the distribution of soil moisture impacts the location and persistence of the storm track and the resulting distribution of precipitation is investigated. Particular attention is given to North America where an extensive series of numerical experiments using a regional climate model are performed to investigate these issues. The findings suggest that soil‐moisture distribution has a pronounced impact on the large‐scale dynamics via a meridional displacement of the storm track. The displacement tends to enhance the local soil moisture–rainfall feedback over the region of the anomaly. The initial feedback is induced by the local effects of soil moisture on the boundary‐layer energy budget and then propagated to the large‐scale through modifications to the geopotential heights. Because of soil moisture's impact on the large‐scale dynamics, a local soil‐moisture anomaly can induce both flood‐ and drought‐like conditions in surrounding regions. Experiments with a dry anomaly applied either over the upper Midwest or Great Plains display a northward shift in the storm track. This shift tends to result in drought‐like conditions in the region of the anomaly and both flood‐ and drought‐like conditions in surrounding regions. Anomalous wetting in the Southwest impacts the distribution of precipitation not only locally, but also over most of the United States; drought‐like conditions are simulated to the north and east of the anomaly region while flood‐like conditions are simulated locally and eastward. Overall, the impacts of soil‐moisture distribution on the large‐scale dynamics and the location and intensity of the storm track play a significant role in determining summer rainfall distribution. Soil‐moisture anomalies over relatively small regions can induce floods and droughts not only locally, but also over remote regions. Copyright © 2003 Royal Meteorological Society.
Characteristics of mixed‐phase clouds. II: A climatology from ground‐based lidar
Authors: Hogan R. J. , Illingworth A. J. , O'connor E. J. , Baptista J. P. V. Poiares
Published: July 2003

In part I it was demonstrated that supercooled liquid‐water clouds can occur in the form of thin but radiatively significant layers that are distinctive in lidar imagery due to their high backscatter coefficient. In this paper, 18 months of near‐continuous lidar data from two midlatitude locations are analysed to estimate the frequency of occurrence of such clouds as a function of temperature. An algorithm is developed that uses the integrated backscatter to identify liquid‐water clouds with a visible optical depth of greater than 0.7 (i.e. those that scatter more than half of the incident radiation), and is found to compare favourably with microwave‐radiometer measurements of liquid‐water path. From data taken with a lidar pointing at 5° from zenith, the frequency of supercooled liquid‐water layers over Chilbolton in southern England is found to fall steadily with temperature; 27% of clouds between −5°C and −10°C are found to contain significant liquid water, falling to only 6% of clouds observed between −25°C and −30°C. The horizontal extent of the layers typically ranges between 20 and 70 km. When the lidar is pointed directly at zenith, specular reflection by horizontally aligned plate crystals is found to bias the statistics between −10°C and −20°C. The importance of supercooled liquid‐water clouds in the radiation budget is reduced when thick ice clouds are present above them, so we then use simultaneous cloud radar data to estimate the optical depth of any cloud above. It is found that around 30% of supercooled liquid‐water clouds with temperatures between 0°C and −20°C have ice above with a visible optical depth in excess of 0.5, falling to 10% between −20°C and −30°C. Given the substantial optical depth of the supercooled water itself, we conclude that in the majority of cases when supercooled water is present, it will dominate the radiative properties of the cloud profile. Finally, we compare the occurrence of supercooled‐liquid clouds with the amounts found in the models of the UK Met Office and the European Centre for Medium‐Range Weather Forecasts (ECMWF). Both models are found to produce too much supercooled liquid at warmer temperatures and too little at colder temperatures (with virtually none being simulated below −20°C), although the occurrence of supercooled cloud is far higher in the ECMWF model than the Met Office model. The observations in this paper are limited to one climatic zone but the forthcoming spaceborne lidars will be able to extend these comparisons to the whole globe. Copyright © 2003 Royal Meteorological Society.
Predictability study of the observed and simulated European climate using linear regression
Authors: Blender Richard , Luksch Ute , Fraedrich Klaus , Raible Christoph C.
Published: July 2003

Monthly mean temperature anomalies in the regions England, Germany and Scandinavia are predicted by linear regression. Two predictors are selected from monthly mean teleconnection indices, North Atlantic sea surface temperatures (SSTs) projected on the first three empirical orthogonal functions (EOFs), and European climate variables (temperature, sea level pressure, and precipitation) averaged in the three predictand regions. The predictors are chosen separately for each month according to their correlation with the predictand. Observations from 1870–1999 and data from a 600‐year integration with the coupled atmosphere– ocean general‐circulation model ECHAM/HOPE are used to assess and compare the forecast skill. The skill is measured by the anomaly correlation coefficient (ACC) and the explained variance (EV).

For a one‐month lead time the ACC for observations is up to 0:6 (EV≈35%) for February–March and August–September in the three regions. The skill for the simulated data is lower (maximum values at ACC≈0:5,EV≈25%) and its seasonal dependence differs from that of the observations. Main predictors are the preceding temperatures in the predictand region. Using segments of the simulated data the spread of skill is estimated as 0.1 in ACC (10% in EV).

For lead times up to one year there is a small ACC (0.3–0.4) in the observations for England (spring and late summer), and Scandinavia (August–September), but none in Germany. The observed two‐month mean England temperature in spring and late summer can be predicted with six months' lead time for 1971–96 with 1870–1969 as a training set, selecting the first two North Atlantic SST EOF coefficients as predictors. A leave‐two‐out cross‐validation in 1870–1999 shows a distinct reduction of skill. In simulated data, the skill beyond one month is negligible compared with the observations. Copyright © 2003 Royal Meteorological Society.
Comparing mass‐consistent atmospheric moisture budgets on an irregular grid: An Arctic example
Authors: Göber M. , Hagenbrock R. , Ament F. , Hense A.
Published: July 2003

We present a method to minimize the effects of different resolution and mass imbalance when comparing atmospheric energy and water budgets from different datasets. Sizeable differences between re‐analysis‐ and radiosonde‐based atmospheric budgets had been found in earlier studies and it had been suspected that the different resolutions of the datasets strongly contributes to these discrepancies. Furthermore, most studies so far had used mass‐imbalanced wind fields, which can lead to serious errors. We balance the wind field by using a variational modification algorithm combined with a finite‐element discretization which allows the use of data on a grid defined by the radiosonde network. This method permits the computation of flux divergences in integral form and gives a consistent numerical method to get a mass‐balanced wind field with minimum modifications.

Applying this method to Arctic radiosonde and re‐analysis data on the same grid leads to a better agreement with respect to the horizontal distribution and the mean annual cycle of the moisture flux convergence. The constraint of mass balance on the wind field leads to a greatly reduced and more realistic variability in space and time. However, a systematic difference of about 20% remains between the estimate based on a re‐analysis dataset sampled only on the coarse grid of the radiosonde network and an estimate based on the use of the full, fine grid of the re‐analysis. These systematic differences can be significantly reduced by creating a simulated radiosonde dataset from the re‐analysis with doubled resolution. We undertake an extensive analysis of the uncertainty of the estimates originating from the choices made in the specification of the algorithm. Based solely on radiosonde data, which are likely to result in a low bias, we estimate the net water gain of the Arctic atmosphere as 164 ± 10 mm yr−1 (0.45 ± 0.03 mm d−1) for 1979–93. Copyright © 2003 Royal Meteorological Society.
Forcing singular vectors and other sensitive model structures
Authors: Barkmeijer J. , Iversen T. , Palmer T. N.
Published: July 2003

Model tendency perturbations can, like analysis perturbations, be an effective way to influence forecasts. In this paper, optimal model tendency perturbations, or forcing singular vectors, are computed with diabatic linear and adjoint T42L40 versions of the European Centre for Medium‐Range Weather Forecasts' forecast model. During the forecast time, the spatial pattern of the tendency perturbation does not vary and the response at optimization time (48 hours) is measured in terms of total energy. Their properties are compared with those of initial singular vectors, and differences, such as larger horizontal scale and location, are discussed. Sensitivity calculations are also performed, whereby a cost function measuring the 2‐day forecast error is minimized by only allowing tendency perturbations. For a given number of minimization steps, this approach yields larger cost‐function reductions than the sensitivity calculation using only analysis perturbations. Nonlinear forecasts using only one type of perturbation confirm an improved performance in the case of tendency perturbations. For a summer experiment a substantial reduction of the systematic error is shown in the case of forcing sensitivity. Copyright © 2003 Royal Meteorological Society.
Linking boundary‐layer variability with convection: A case‐study from JET2000
Authors: Taylor C. M. , Ellis R. J. , Parker D. J. , Burton R. R. , Thorncroft C. D.
Published: July 2003

The properties of the planetary boundary layer (PBL) are crucial for understanding convection and dynamics in the tropical atmosphere. In semi‐arid regions, there are strong links between the PBL and soil moisture. This study demonstrates the link between PBL characteristics and antecedent rainfall via soil moisture variability on length‐scales from 10 to 100 km. Spatial variability of the PBL in the west African Sahel is explored using observations from an aircraft for one day in the wet season, as part of the JET2000 experiment. Meteosat and surface station data provide information about rainfall patterns during the previous days.

The aircraft transect crossed several well‐defined bands of low surface temperature and albedo, as determined by the satellite imagery. These bands indicate high soil moisture beneath the paths of recent storms. Observed atmospheric properties are closely linked to the surface gradients. Above moist soils, the PBL tends to be shallower, cooler, moister and less turbulent than in adjacent dry areas. The study shows that the characteristic large‐scale gradients of temperature and humidity across the Sahel are concentrated in zones defined by recent rainfall.

Evidence is presented which is consistent with a positive feedback at the storm‐scale between deep convection and soil moisture. Atmospheric profiles indicate that soil moisture plays an important role in determining the stability of the atmosphere to subsequent convection. It was found that in a region of low surface moisture covering 80000 km2, cold‐cloud systems did not occur in the 48 hours following the flight. By contrast, mesoscale convective systems were observed in adjacent regions with wetter soils. Copyright © 2003 Royal Meteorological Society.
Horizontal and temporal variability of mountain waves over Mont Blanc
Authors: Smith S. A. , Broad A. S.
Published: July 2003

Aircraft observations of mountain waves over Mont Blanc during the 2 November 1999 Mesoscale Alpine Programme (MAP) case‐study are analysed. The present paper focuses on the horizontal and temporal variability of the wave field and its momentum fluxes. Results from the first Met Office Unified Model new‐dynamics simulation of a real mountain‐wave case are presented. The wave field and its fluxes are reproduced reasonably well considering the complexity of the problem.

The wave momentum fluxes are observed to be extremely variable, which is surprising considering the stationarity of the wave field, although some variation is observed in the vertical‐velocity magnitude. The flux variability may result from the increasing midtropospheric wind shear with time. The simulated wind fields are used to investigate the horizontal variability in the wave field. The along‐track wave momentum flux is affected only slightly by a 2 km change in the position of the transect relative to Mont Blanc due to its displacement from the centre of the wave. More important in this particular case is the effect of the averaging length on the flux profile due to the limited downstream extent of the wave field, with large fluxes observed immediately over Mont Blanc. However, the position of the transect affects the apparent extent of the wave field and the magnitude of the variation in the cross‐wind component. © Crown copyright 2003.
Solar radiative transfer for stratiform clouds with horizontal variations in liquid‐water path and droplet effective radius
Authors: Räisänen Petri , Isaac George A. , Barker Howard W. , Gultepe Ismail
Published: July 2003

Effects of horizontal variations in liquid‐water path (LWP) and droplet effective radius (re) on solar radiative‐transfer properties of stratiform clouds are addressed. To this end, a broadband Monte Carlo solar radiation code and in situ aircraft observations of cloud properties collected in the Radiation, Aerosol and Cloud Experiment are used. The experiments confirm that the radiative impact of cloud horizontal inhomogeneity is dominated by variations in LWP, which make cloud short‐wave albedo smaller than that for a corresponding plane‐parallel horizontally homogeneous cloud. When horizontal variations in re are accounted for, however, the impact due to horizontal variations in LWP is usually reduced. When re and LWP are highly correlated, as is typically the case, the impact on albedo due to LWP variations alone can be reduced easily by 30% when variations in re are included. Uncertainty factors involved in the calculations are also discussed. Copyright © 2003 Royal Meteorological Society.
Impact of temperature and humidity variability on cloud cover assessed using aircraft data
Authors: Tompkins A. M.
Published: July 2003

Aircraft thermodynamic measurements taken in liquid‐water clouds over the North American Great Plains are analysed to assess the relative importance of temperature and humidity fluctuations for cloud cover. It is found that the effect of temperature variability is roughly half that of humidity. Thus, although the representation of humidity variability in models is the primary task, the parametrization of temperature perturbations is also desirable. This aim would be easier if temperature and humidity fluctuations were correlated, since a diagnostic parametrization may then be possible. Examination of the data reveals that the majority of events show a negative correlation, in agreement with previous observations. Moreover, the cloud cover error is significantly smaller in the cases where temperature and humidity perturbations are uncorrelated for two reasons. Firstly, the de‐correlation is likely to be the result of a faster dissipation time‐scale for temperature fluctuations, which also reduces their magnitude and thus importance. Secondly, it is shown that there is a significant cancellation of cloud cover errors when no correlation between temperature and humidity exists. A simple estimate of the temperature/humidity correlation is made assuming vertical adiabatic motion is the only source of horizontal fluctuations, and it is found to produce a close fit to the data in some instances, mostly when the magnitude of the temperature fluctuations is larger, as predicted. In summary, the analysis implies that a simple diagnostic parametrization for temperature fluctuations may be helpful and indeed possible. Copyright © 2003 Royal Meteorological Society.
Evaluation of the AIRS near‐real‐time channel selection for application to numerical weather prediction
Authors: Fourri'e Nadia , Thépaut Jean‐noël
Published: July 2003

The Atmospheric Infrared Sounder (AIRS) on board the National Aeronautics and Space Administration (NASA) Earth Observing System (EOS) Aqua satellite provides 2378 channels for each field of view of the instrument. As it is neither feasible nor efficient to assimilate all the channels in a numerical weather‐prediction system, a policy of channel selection has to be designed in this context. This paper attempts to assess the optimality of the selection of the AIRS radiance channels that are made available to the scientific community in near real time (hereafter called AIRS NRT) by the National Oceanic and Atmospheric Administration (NOAA) National Environmental Satellite Data and Information Service. This assessment is done by comparing this channel selection with a method preserving the information content of the instrument, the so‐called ‘global’ method. It turns out that although the selected channels are different and the information content as measured by the entropy reduction (ER) and the degrees of freedom for signal (DFS) is slightly smaller for the AIRS NRT channel set than for the ‘global’ set, both channel selections give similar results in terms of analysis error for temperature, humidity and ozone. The robustness of the results is then evaluated by varying the range of input parameters to the channel‐selection scheme, in particular the atmospheric training dataset on which the channel selection is based, and the background‐error covariance matrix. It is found that the performance of the ‘global’ channel selection is sensitive to the training dataset, while the AIRS NRT channel selection remains robust, even, to some extent, for the retrieval of key analysis‐error structures. Altogether, the ‘manually selected’ AIRS NRT channels provide a good compromise between robustness and quality. Copyright © 2003 Royal Meteorological Society.