| 711. |
- HO, CH, et al.
(författare)
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Influence of stratospheric quasi-biennial oscillation on tropical cyclone tracks in the western North Pacific
- 2009
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Ingår i: GEOPHYSICAL RESEARCH LETTERS. - 0094-8276. ; 36
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Tidskriftsartikel (refereegranskat)abstract
- The possible influence of the stratospheric quasi-biennial oscillation (QBO) on tropical cyclone (TC) passages in the western North Pacific (WNP) is examined using TC data recorded by the Tokyo Typhoon Center and the QBO index derived from reanalysis data. The influence is observed to be significant. The number of TCs approaching the East China Sea is large during the westerly phase of the QBO; however, during the easterly phase, the number of TCs approaching the eastern offshore of Japan is large. This difference in the TC tracks is found to be related to the background flow change associated with the QBO. However, the total number of TC events over the WNP and the sum of the number of TCs approaching the aforementioned two regions appear to be unrelated to the QBO phases. Citation: Ho, C.-H., H.- S. Kim, J.- H. Jeong, and S.-W. Son (2009), Influence of stratospheric quasi-biennial oscillation on tropical cyclone tracks in the western North Pacific, Geophys. Res. Lett., 36, L06702, doi:10.1029/2009GL037163.
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| 712. |
- Ito, A., et al.
(författare)
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Cold-Season Methane Fluxes Simulated by GCP-CH4 Models
- 2023
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Ingår i: Geophysical Research Letters. - 0094-8276. ; 50:14
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Tidskriftsartikel (refereegranskat)abstract
- Cold-season methane (CH4) emissions may be poorly constrained in wetland models. We examined cold-season CH4 emissions simulated by 16 models participating in the Global Carbon Project model intercomparison and analyzed temporal and spatial patterns in simulation results using prescribed inundation data for 2000–2020. Estimated annual CH4 emissions from northern (>60°N) wetlands averaged 10.0 ± 5.5 Tg CH4 yr−1. While summer CH4 emissions were well simulated compared to in-situ flux measurement observations, the models underestimated CH4 during September to May relative to annual total (27 ± 9%, compared to 45% in observations) and substantially in the months with subzero air temperatures (5 ± 5%, compared to 27% in observations). Because of winter warming, nevertheless, the contribution of cold-season emissions was simulated to increase at 0.4 ± 0.8% decade−1. Different parameterizations of processes, for example, freezing–thawing and snow insulation, caused conspicuous variability among models, implying the necessity of model refinement.
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| 713. |
- Janhunen, P, et al.
(författare)
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The closure of region-1 field-aligned current in MHD simulation
- 1997
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Ingår i: GEOPHYSICAL RESEARCH LETTERS. - : AMER GEOPHYSICAL UNION. - 0094-8276. ; 24:11, s. 1419-1422
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We have studied the closure path of Region-1 field-aligned current system in our global MHD simulation and found some interesting results. After leaving the ionosphere on the eveningside the current deviates from the field-aligned direction rather early a
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| 714. |
- JEONG, SJ, et al.
(författare)
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Increase in vegetation greenness and decrease in springtime warming over east Asia
- 2009
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Ingår i: GEOPHYSICAL RESEARCH LETTERS. - 0094-8276. ; 36
-
Tidskriftsartikel (refereegranskat)abstract
- This study investigates the impact of increased vegetation greening on the springtime temperature over east Asia for 1982-2000. An analysis of station-based temperature records and satellite-measure normalized difference vegetation index (NDVI) indicates that slight warming (<0.4 degrees C 10-yr(-1)) occurred over regions that experienced large increase in NDVI (>= 0.08 10-yr(-1)). On the contrary, strong warming (>= 0.8 degrees C 10-yr(-1)) occurred over regions that exhibited minor changes in NDVI (<0.04 10-yr(-1)). For the most part, this inverse NDVI-temperature relationship observed with the daily maximum temperature. Thus, it is suggested that the decrease in warming was mostly attributable to the increase in evapotranspiration associated with increased vegetation greening. Earlier vegetation growth may have further strengthened the effect of this vegetation-evaporation on spring temperature. Citation: Jeong, S.-J., C.-H. Ho, and J.-H. Jeong (2009), Increase in vegetation greenness and decrease in springtime warming over east Asia, Geophys. Res. Lett., 36, L02710, doi: 10.1029/2008GL036583.
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| 715. |
- JEONG, SJ, et al.
(författare)
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Reduction of spring warming over East Asia associated with vegetation feedback
- 2009
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Ingår i: GEOPHYSICAL RESEARCH LETTERS. - 0094-8276. ; 36
-
Tidskriftsartikel (refereegranskat)abstract
- Over East Asia, surface air temperature displays a significant increasing trend particularly in early months of the year for the period of 1982-2000. Warming per decade is strongest in late winter, 1.5 degrees C in February and 1.1 degrees C in March, but is significantly reduced in spring, 0.4 degrees C in April and 0.1 degrees C in May. During the analysis period, the reduced temperature increase from late winter to spring is found to be in contrast with the increased vegetation greenness derived from the satellite-measured leaf area index over the domain. We examined this inverse relationship using two climate model experiments-coupled with and without a dynamic vegetation model. In both experiments, strong warming in winter is relatively well reproduced, but weak warming in spring is observed only in the coupled experiment. Analysis of the surface energy budget indicates that weaker spring warming results from an evaporative cooling effect due to the increased vegetation greenness. Over East Asia, the vegetation-evaporation feedback, therefore, may produce seasonal asymmetry in the warming trend. Citation: Jeong, S.-J., C.-H. Ho, K.-Y. Kim, and J.-H. Jeong (2009), Reduction of spring warming over East Asia associated with vegetation feedback, Geophys. Res. Lett., 36, L18705, doi: 10.1029/2009GL039114.
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| 716. |
- Jin, Yishuai, et al.
(författare)
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Controls of Spring Persistence Barrier Strength in Different ENSO Regimes and Implications for 21st Century Changes
- 2020
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Ingår i: Geophysical Research Letters. - 0094-8276. ; 47:11
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Tidskriftsartikel (refereegranskat)abstract
- This paper investigates potential factors that control the El Niño–Southern Oscillation (ENSO) Spring Persistence Barrier (SPB) strength in two different ENSO regimes and apply it to explain the ENSO SPB strength modulation after the 21st century. In a damped, noise-driven model, the theoretical solution of SPB strength illustrates that a weaker ENSO growth rate strengthens SPB. In the self-sustained regime, as in the Cane-Zebiak model (chaotic system), the strengthened thermodynamic damping and weakened thermocline positive feedback lead to a more negative ENSO growth rate and, in turn, a stronger SPB. Therefore, in both ENSO regimes, a weaker ENSO growth rate intensifies the SPB. The application of the theory to the real world suggests that a more negative ENSO growth rate, corresponding to a more damped feedback system, is responsible for the stronger SPB in recent decades than in 1980–2000.
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| 717. |
- Jin, Yishuai, et al.
(författare)
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Seasonal Cycle of Background in the Tropical Pacific as a Cause of ENSO Spring Persistence Barrier
- 2019
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Ingår i: Geophysical Research Letters. - 0094-8276. ; 46:22, s. 13371-13378
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Tidskriftsartikel (refereegranskat)abstract
- Statistical model results suggest that the declining growth rate from autumn to spring is the key to cause El Niño-Southern Oscillation (ENSO) spring persistence barrier (SPB). Using a dynamical approach, we develop the physical mechanisms responsible for ENSO SPB in the framework of recharge oscillator by adding a seasonally varying Bjerknes (BJ) stability index and linking it with ENSO growth rate. By decomposing BJ index, it is indicated that seasonal thermodynamic damping and thermocline positive feedback play an important role in determining the ENSO SPB. We further show that the increasing/decreasing upper-level cloud/low-level cloud and the deepening thermocline from autumn to spring are the main factors to control the SPB of ENSO. Our proposed mechanisms also have useful implications for the understanding of ENSO prediction.
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| 718. |
- Kaniewski, David, et al.
(författare)
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Climate Change and Social Unrest: A 6,000‐Year Chronicle From the Eastern Mediterranean
- 2020
-
Ingår i: Geophysical Research Letters. - 0094-8276. ; 47:7
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Tidskriftsartikel (refereegranskat)abstract
- The history of the Eastern Mediterranean is punctuated by major crises that have influenced many of the region's established socioeconomic models. Recent studies have underscored the role of drought and temperature oscillations in driving changes but attempts to quantify their magnitude remain equivocal, hindering long‐term assessments of the potential interplay between climate and society. Here, we fill this knowledge gap using a 6,000‐year pollen‐based reconstruction of temperature and precipitation from Hala Sultan Tekke, Cyprus. We find that major social changes and plague outbreaks often occurred in tandem with cooler climate conditions, with anomalies ranging from −3 ± 0.4 °C to −1 ± 0.5 °C, coupled with changing precipitation patterns. We suggest that major climate changes may weaken societies by affecting primary livelihood systems. This long‐term view highlights recurrent cold periods in the Eastern Mediterranean's climate history and advocates that, despite frequent adversity and pandemics, Near Eastern populations adapted and were ultimately resilient to major climate changes.
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| 719. |
- KAURISTIE, K, et al.
(författare)
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ANALYSIS OF THE SUBSTORM TRIGGER PHASE USING MULTIPLE GROUND-BASED INSTRUMENTATION
- 1995
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Ingår i: GEOPHYSICAL RESEARCH LETTERS. - : AMER GEOPHYSICAL UNION. - 0094-8276. ; 22:15, s. 2065-2068
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- During the substorm trigger phase, i.e. during the last few minutes before the onset, the slowly and linearly developing growth phase features strengthen exponentially. Often the enhanced auroral activity fades abruptly during a couple of minutes just pri
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| 720. |
- Kiendler-Scharr, A., et al.
(författare)
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Ubiquity of organic nitrates from nighttime chemistry in the European submicron aerosol
- 2016
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Ingår i: Geophysical Research Letters. - 0094-8276. ; 43:14, s. 7735-7744
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Tidskriftsartikel (refereegranskat)abstract
- In the atmosphere nighttime removal of volatile organic compounds is initiated to a large extent by reaction with the nitrate radical (NO3) forming organic nitrates which partition between gas and particulate phase. Here we show based on particle phase measurements performed at a suburban site in the Netherlands that organic nitrates contribute substantially to particulate nitrate and organic mass. Comparisons with a chemistry transport model indicate that most of the measured particulate organic nitrates are formed by NO3 oxidation. Using aerosol composition data from three intensive observation periods at numerous measurement sites across Europe, we conclude that organic nitrates are a considerable fraction of fine particulate matter (PM1) at the continental scale. Organic nitrates represent 34% to 44% of measured submicron aerosol nitrate and are found at all urban and rural sites, implying a substantial potential of PM reduction by NOx emission control.
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