Pacific Storm Research Articles

Combined effects of La Niña events and Arctic tropospheric warming on the winter North Pacific storm track

Combined effects of La Niña events and Arctic tropospheric warming on the winter North Pacific storm track

Mechanical and Thermal Impacts of the Tibetan–Iranian Plateau on the North Pacific Storm Track: Numerical Experiments by FGOALS‐f3‐L

AbstractBy employing a state‐of‐the‐art global atmospheric general circulation model from the Global Monsoons Model Inter‐comparison Project, this study investigates the mechanical and thermal impacts of the Tibetan‐Iranian Plateau (TIP) on the North Pacific storm track (NPST). When the TIP‐associated mechanical forcing is removed, the winter NPST strengthens remarkably on the northern flank of its climatological maximum and becomes inconspicuously separated from storm track activities over the Asian continent. The midwinter suppression of the NPST is almost inapparent but still exists. In contrast, when TIP‐associated thermal forcing is absent, the winter NPST amplitudes weaken prominently on the north and west sides, and the midwinter suppression remains obvious. The mechanical and thermal impact of the TIP on the NPST are robust not only in winter but also in other seasons. Without the TIP‐associated mechanical forcing, the intensified winter NPST may be dependent on the weakened and widened upper‐level jet, strengthened atmospheric baroclinicity on the north side of climatological winter upper‐level jet, enhanced baroclinic energy conversion, and attenuated East Asian trough. In contrast, without the TIP‐associated thermal forcing, the weakened winter NPST may be determined by the strengthened and narrowed upper‐level jet, reduced atmospheric baroclinicity on the northern flank of upper‐level jet, decreased baroclinic energy conversion, and intensified East Asian trough.

Holocene water levels of Silver Lake, Montana, and the hydroclimate history of the Inland Northwest

AbstractThe wettest portion of the interior of western North America centers on the mountainous region spanning western Montana, Idaho, British Columbia, and Alberta. Inland ranges there capture the remnants of Pacific storms. Steep east–west hydroclimate gradients make the region sensitive to changes in inland-penetrating moisture that may have varied greatly during the Holocene. To investigate potential hydroclimate change, we produced a 7600-yr lake-level reconstruction from Silver Lake, located on the Montana–Idaho border. Ground-penetrating radar profiles and a transect of four shallow-water sediment cores that were dated using radiocarbon dating and tephrachronology revealed substantial changes in moisture through time. An organic-rich mud unit indicating wet and similar to modern conditions prior to 7000 cal yr BP is overlain by an erosional surface signifying drier than modern conditions from 7000–2800 cal yr BP. A subsequent time-transgressive increase in water levels from 2800–2300 cal yr BP is indicated by a layer of late Holocene muds, and is consistent with glacier expansion and increases in the abundance of mesic tree taxa in the region. Millennial-scale trends were likely driven by variations in orbital-scale forcing during the Holocene, but the regional outcomes probably depended upon factors such as the strength of the Aleutian Low, Pacific sea-surface temperature variability, and the frequency of atmospheric rivers over western North America.

Effect of North Pacific Storm Track on Winter Temperature in China

Effect of North Pacific Storm Track on Winter Temperature in China

Bound to the Land: Cove Fort in Kesler Family History and Memory

Bound to the Land: Cove Fort in Kesler Family History and Memory

Rapid Increase of Explosive Cyclone Activity over the Midwinter North Pacific in the Late 1980s

Abstract Long-term changes in the activity of explosively developing “bomb” cyclones over the wintertime North Pacific are investigated by using a particular version of a global atmospheric reanalysis dataset into which only conventional observations have been assimilated. Bomb cyclones in January are found to increase rapidly around 1987 in the midlatitude central North Pacific. Some of the increased bomb cyclones formed over the East China Sea and then moved along the southern coast of Japan before developing explosively in the central North Pacific. The enhanced cyclone activity is found to be concomitant with rapid warming and moistening over the subtropical western Pacific and the South and East China Seas under the weakened monsoonal northerlies, leading to the enhancement of the lower-tropospheric Eady growth rate and equivalent potential temperature gradient, setting a condition favorable for cyclone formation in the area upstream of the North Pacific storm track. Along the storm track, poleward moisture transport in the warm sector of a cyclone and associated precipitation along the warm and cold fronts tended to increase and thereby enhance its explosive development. After the transition around 1987, a bomb cyclone has become more likely to develop without a strong upper-level cyclonic vortex propagating from Eurasia than in the earlier period. The increased bomb cyclone activity in January is found to contribute to the diminished midwinter minimum of the North Pacific storm track activity after the mid-1980s.

Comparing Frontal Structures of Extratropical Cyclones in the Northwestern Pacific and Northwestern Atlantic Storm Tracks

Abstract The frontal structures of extratropical cyclones developing in the northwestern Pacific storm track are relatively poorly understood compared with those in Europe and the Atlantic Ocean, for which representative conceptual models have been developed. In this paper, the structures of cyclones and their associated fronts in the northwestern Pacific (NP), as well as in the Okhotsk Sea and Sea of Japan (OJ), are examined at their developing and mature stages using Japanese 55-year Reanalysis dataset. Furthermore, the frontal structures in the NP are compared with those in the northwestern Atlantic (NA). At the time of maximum deepening rate, cyclones in the NP are accompanied by strong warm and cold fronts, whereas cyclones in the OJ are more frequently accompanied by cold fronts than by warm fronts and tend to have stronger cold fronts than warm fronts. The weaker warm fronts than cold fronts to the east and northeast of cyclones in the OJ is likely due to the cyclones developing to the north and away from the region where the horizontal gradient of environmental potential temperature is strong. A comparison between mature cyclones in the NP and NA shows that the warm fronts in the NA tend to extend northeastward, whereas those in the NP extend more southeastward. These differences in warm fronts between NP and NA are suggested to be due to the difference in the horizontal structures of the warm currents between NP and NA.

The Linkage between Midwinter Suppression of the North Pacific Storm Track and Atmospheric Circulation Features in the Northern Hemisphere

The Linkage between Midwinter Suppression of the North Pacific Storm Track and Atmospheric Circulation Features in the Northern Hemisphere

Multi‐GNSS Airborne Radio Occultation Observations as a Complement to Dropsondes in Atmospheric River Reconnaissance

AbstractVariations in the water vapor that atmospheric rivers (ARs) carry toward North America within Pacific storms strongly modulates the spatiotemporal distribution of west‐coast precipitation. The “AR Recon” program was established to improve forecasts of landfalling Pacific‐coast ARs and their associated precipitation. Dropsondes are deployed from weather reconnaissance aircraft and pressure sensors have been added to drifting ocean buoys to fill a major gap in standard weather observations, while research is being conducted on the potential for airborne Global Navigation Satellite System (GNSS) radio occultation (ARO) to also contribute to forecast improvement. ARO further expands the spatial coverage of the data collected during AR Recon flights. This study provides the first description of these data, which provide water vapor and temperature information typically as far as 300 km to the side of the aircraft. The first refractivity profiles from European Galileo satellites are provided and their accuracy is evaluated using the dropsondes. It is shown that spatial variations in the refractivity anomaly (difference from the climatological background) are modulated by AR features, including the low‐level jet and tropopause fold, illustrating the potential for RO measurements to represent key AR characteristics. It is demonstrated that assimilation of ARO refractivity profiles can influence the moisture used as initial conditions in a high‐resolution model. While the dropsonde measurements provide precise, in situ wind, temperature and water vapor vertical profiles beneath the aircraft, and the buoys provide surface pressure, ARO provides complementary thermodynamic information aloft in broad areas not otherwise sampled at no additional expendable cost.

Inconsistent Variations Between the Northern and Southern North Pacific Storm Track

AbstractIn this study, the North Pacific storm track (PST) is divided into the northern PST (NPST) and southern PST (SPST). The consistencies of the interannual‐to‐interdecadal and climatological variations between the NPST and SPST are investigated. On an interannual‐to‐interdecadal scale, the PST‐related meridional dipole of the upper‐level zonal wind anomalies is largely associated with the NPST. Only the NPST is significantly associated with the North Pacific atmospheric blocking and the Pacific‐North American teleconnection pattern. The NPST‐related sea surface temperature anomalies are confined to the North Pacific. In contrast, the SPST‐related sea surface temperature anomalies basically coincide with the Indian Ocean basin mode and the Pacific Decadal Oscillation. The climatological seasonal cycles of the NPST and SPST exhibit double‐peak and single‐peak structures, respectively, in accordance with the linear baroclinic instability theory. In general, the interannual‐to‐interdecadal and climatological variations in the NPST intensity are inconsistent with those in the SPST intensity.

Change in the variability in the Western Pacific pattern during boreal winter: roles of tropical Pacific sea surface temperature anomalies and North Pacific storm track activity

Using multiple reanalysis datasets, this study reveals that the variability in the western Pacific pattern (WP) in boreal winter has shown notable changes during recent decades. The variability in the winter WP exhibited a marked weakening trend before the early 2000s and increased slightly thereafter. Two epochs with the highest and lowest WP variabilities are selected for a comparative analysis. Winter WP-related meridional dipole atmospheric anomalies over the North Pacific were stronger and had a broader range during the high-variability epoch than during the low-variability epoch. Correspondingly, the winter WP had larger impacts on surface temperature variations over Eurasia and North America during the high-variability epoch than that during the low-variability epoch. We find that the shift in the winter WP variability is closely related to changes in the connection between the winter WP and the El Niño-Southern Oscillation (ENSO) and to changes in the amplitude of the North Pacific storm track. Specifically, ENSO had a closer connection with the WP during the high-variability epoch, when the amplitude of the North Pacific storm track was also stronger. During the high-variability epoch, the extratropical atmospheric anomalies generated by the tropical ENSO shifted westward and projected more on the WP-related atmospheric anomalies, thus contributing to an increase in WP variability. In addition, the larger amplitude of the North Pacific storm track that occurred during the high-variability epoch led to the stronger feedback of synoptic-scale eddies to the mean flow and contributed to stronger WP variability. Further analysis indicates that the change in the connection of ENSO with the WP may be partly related to the zonal shift of the sea surface temperature anomaly in the tropical Pacific associated with ENSO.

Smoother versus sharper Gulf Stream and Kuroshio sea surface temperature fronts: effects on cyclones and climatology

Abstract. The Gulf Stream and Kuroshio regions feature strong sea surface temperature (SST) gradients that influence cyclone development and the storm track. Previous studies showed that smoothing the SSTs in either the North Atlantic or North Pacific yields a reduction in cyclone activity, surface heat fluxes, and precipitation, as well as a southward shift of the storm track and the upper-level jet. To what extent these changes are attributable to changes in individual cyclone behaviour, however, remains unclear. Comparing simulations with realistic and smoothed SSTs in the atmospheric general circulation model AFES, we find that the intensification of individual cyclones in the Gulf Stream or Kuroshio region is only marginally affected by reducing the SST gradient. In contrast, we observe considerable changes in the climatological mean state as well as a reduced cyclone activity in the North Atlantic and North Pacific storm tracks that are shifted equatorward in both basins. The upper-level jet in the Atlantic also shifts equatorward, while the jet in the Pacific strengthens in its climatological position and extends further east. Surface heat fluxes, specific humidity, and precipitation also respond strongly to the smoothing of the SST, with a considerable decrease in their mean values on the warm side of the SST front. This decrease is more pronounced in the Gulf Stream than in the Kuroshio region, due to the larger decrease in SST along the Gulf Stream SST front. Considering the differences of the different variables occurring within/outside of a 750 km radius of any cyclone over their entire lifetime, we find that cyclones play only a secondary role in explaining the differences in the mean state between the smoothed and realistic SST experiments.

Are the Different Eddy Metrics Quantifying the Winter North Pacific Storm Track Consistent With Each Other?

AbstractHistorical simulations from twenty‐nine Coupled Model Intercomparison Project Phase 6 (CMIP6) models are used to investigate the consistency among different eddy metrics characterizing the winter North Pacific storm track (WNPST). All CMIP6 models can reproduce the basic climatological characteristics of the WNPST. Results show that, out of the metrics studies, only the upper‐tropospheric filtered meridional wind variance () is significantly correlated with the model grid spacing. The climatological amplitudes of different eddy metrics are consistent with each other, except for the consistency between the upper‐tropospheric and lower‐tropospheric meridional eddy heat flux and that between the middle‐tropospheric eddy kinetic energy and filtered sea level pressure variance (). The strength trends of different eddy metrics are consistent with each other except for upper‐tropospheric and . The meridional migration trends are consistent among different eddy metrics excluding . Given that the sensitivity to horizontal resolution, climatological amplitude, strength trend and meridional migration trend of different Eulerian eddy metrics may exhibit inconsistency, the use of multiple eddy metrics to increase the reliability of the results is suggested.

Influence of Atmospheric Blocking on Storm Track Activity Over the North Pacific During Boreal Winter

AbstractThe observed interannual impact of the North Pacific atmospheric blocking (PB) on the North Pacific storm track (PST) during boreal winter is investigated. There is a significant out‐of‐phase relationship between the intensities of PB and PST. The strong PB is accompanied by prominent geopotential height anomalies exhibiting a meridional dipole. PB‐related anomalous easterlies south of the anticyclonic anomaly reduce the low‐level atmospheric baroclinicity by weakening the upper‐level zonal wind, which may be responsible for the attenuated PST. The situations are opposite when PB is weak but with relatively weak magnitudes. However, the intensified PST associated with weak PB may not be determined by the strengthened baroclinicity. Additionally, by diagnosing the energy budget, the contribution of energy conversion from background available potential energy to the altered eddy available potential energy (EAPE) can be elucidated. PB‐related anomalous baroclinic energy conversion from EAPE to eddy kinetic energy (EKE) largely explains the altered EKE.

A Multi‐Inventory Ensemble Analysis of the Effects of Atmospheric Rivers on Precipitation and Streamflow in the Namgang‐Dam Basin in Korea

AbstractAtmospheric rivers (ARs) are an important concern in regional water management; however, little is known about the AR impacts on hydrology in East Asia (EA). This study analyzes the characteristics of storms, precipitation (P), streamflow (Q), and runoff coefficient (R) in the Namgang‐dam basin in Korea related to ARs for 2000–2013, as well as the sensitivity of the analysis results to AR detection methods, using observed P, Q, and three different AR inventories. The basin experiences 37.3 storms annually, of which 54% are AR storms that provide over 60% of the annual P and Q. The AR (non‐AR) storms are dominant in storm frequency and the storm‐total P and Q for January–July (August–December) with peaks in July (August). The monthly AR frequency varies closely with the seasonal variations in the EA monsoon and the North Pacific storm track which modulate the number of extratropical cyclones. The AR storms produce most of the extreme events; they also generate larger storm‐mean P and Q than the non‐AR storms for all months. The seasonal variations in R are related to the total (AR‐ and non‐AR storms combined) P through the seasonal soil water variations, making the AR effects on R unclear. Considering 95% confidence intervals, the AR storms are distinguished well from the non‐AR storms in storm frequency and the storm‐total and storm‐mean P and Q. The sensitivity to AR inventories is not critical in quantifying the AR‐storm characteristics and their impacts on hydrologic variables except for R.

The Climatology and the Midwinter Suppression of the Cold Season North Pacific Storm Track in CMIP6 Models

AbstractThe reproducibility of climatology and the midwinter suppression of cold season North Pacific storm track (NPST) in historical runs of 18 CMIP6 models is evaluated against the NCEP reanalysis data. The results show that the position of the climatological peak area of 850 hPa meridional eddy heat flux (v′t′850) is well captured by these models. The spatial patterns of climatological v′t′850 are basically consistent with the NCEP reanalysis. Generally, NorESM2-LM and CESM2-WACCM present a relatively strong capability to reproduce the climatological amplitude of v′t′850 with lower RMSE than the other models. Compared with CMIP5 models, the inter-model spread of v′t′850 climatology among the CMIP6 models is smaller, and their multi-model ensemble is closer to the NCEP reanalysis. The geographical distribution in more than half of the selected models is further south and east. For the subseasonal variability of v′t′850, nearly half of the models exhibit a double-peak structure. In contrast, the apparent midwinter suppression in the NPST represented by the 250 hPa filtered meridional wind variance (v′v′250) is reproduced by all the selected models.In addition, the present study investigates the possible reasons for simulation biases regarding climatological NPST amplitude. It is found that a higher model horizontal resolution significantly intensifies the climatological v′v′250. There is a significant in-phase relationship between climatological v′t′250 and the intensity of the East Asian winter monsoon (EAWM). However, the climatological v′t′850 is not sensitive to the model grid spacing. Additionally, the climatological low-tropospheric atmospheric baroclinicity is uncorrelated with climatological v′v′250. The stronger climatological baroclinic energy conversion is associated with the stronger climatological v′t′850.

Analysis of Correlation and Coupling between El Niño-Southern Oscillation and Dust Storms in Iraq from 1971 to 2016

This study's main objective is to examine the impact of the El Niño-Southern Oscillation on dust storms in Iraq and trying to find a reasonable synoptic explanation of this relationship. In order to achieve our goal, various data collections related to dust storm days from eight stations in Iraq and the El Niño-Southern Oscillation data over the period 1971–2016 were analyzed. The results showed a negative relationship between dust storms and the El Niño-Southern Oscillation. This correlation means high dust storms are associated with La Niña, while the low dust storms occur during the El Niño event. The coupling between the tropical pacific sector and dust storms in Iraq is perhaps related to the El Niño-Southern Oscillation variations and how they can contribute to the change of the main pressure system values that mainly participate in triggering dust storms and their intensity. The subtropical high-pressure and the Indian monsoon low-pressure systems have been recognized as the responsible pressure systems for dust storms formation.

IMPACT OF ARCTIC SEA ICE REDUCTION ON ATMOSPHERIC CIRCULATION PATTERNS

This paper focuses on the effect of sea ice melting under the effect of the mechanism of decreasing albedo of dry and wet ice and snow on the structure of atmospheric circulation. In particular, the Impact on storm tracks in the Pacific and Atlantic Oceans is analyzed. Extreme weather events are usually associated with atmospheric blocking conditions. Blocking is such meteorological conditions in which a large anticyclonic atmospheric vortex is observed over an area for several days. The Molteni-Tibaldi blocking criterion and the magnitude of the local anticyclonic wave activity (LAWA) are used to estimate the number of blockings. Extreme values of LAWA may indicate the presence of atmospheric blockings. As a result, there is a weakening and eastward shift of Atlantic storm trajectories. There is almost no influence on the Pacific storm tracks.

Interdecadal Change in the Relationship between the Winter North Pacific Storm Track and the East Asian Winter Monsoon

AbstractBased on the daily NCEP reanalysis, the present study investigates the interdecadal change in the relationship between the winter North Pacific storm track (WNPST) and the East Asian winter monsoon (EAWM), and evaluates the WNPST–EAWM relationship in 17 CMIP6 models. The results show that the out-of-phase WNPST–EAWM relationship underwent an interdecadal change in the mid-1980s. The WNPST–EAWM relationship became less significant during period 2 (P2; 1990–2015). The atmospheric circulation anomaly related to the EAWM during period 1 (P1; 1955–80) is more robust than that during P2. The interdecadal weakening WNPST–EAWM relationship may be attributed to the interdecadal damping WNPST–EAWM interaction. The EAWM-related anomalous baroclinic energy conversion and moisture effects, including meridional and vertical eddy moisture fluxes, contribute to the significant attenuation of the WNPST during P1. The transient eddy-induced dynamic forcing and thermal forcing anomalies, as well as the barotropic process represented by the local Eliassen–Palm flux divergence associated with WNPST, can also significantly manipulate the upper-tropospheric jet during P1. However, the atmospheric circulation and interaction between the WNPST and EAWM during P2 are not as significant as those during P1. The effect of ENSO on the WNPST is significantly different before and after the mid-1980s. After the mid-1980s, the WNPST shows the characteristic of moving equatorward during El Niño events. It seems that ENSO takes over the WNPST from the EAWM after the mid-1980s. In addition, except for BCC-ESM1, CanESM5, and SAM0-UNICON, most of the CMIP6 models cannot reproduce the significant out-of-phase WNPST–EAWM relationship.

Association of the Zonal Migration of North Pacific Storm Track With the East Asian Monsoon in Boreal Wintertime

AbstractThe winter North Pacific storm track (WNPST) distinctly manipulates weather and climate in the midlatitudes. Thus, it is necessary to comprehend the factors and related mechanisms governing the location and intensity of WNPST. In the present study, the influence of the East Asian winter monsoon (EAWM) on the zonal movement of the WNPST represented by the lower‐tropospheric meridional eddy heat flux is investigated, and the possible physical processes are analyzed. There is a significantly positive correlation, especially interannual signal, between the strength of the EAWM and the zonal position of the WNPST. The Liang‐Kleeman information flow theory is used to prove the mutual causality between the intensity of EAWM and the zonal migration of WNPST. The EAWM‐related intensity anomaly pattern of the WNPST, with prominently negative anomalies over the northwest Pacific and significantly positive anomalies over the northeast Pacific, is associated with the eastward movement of the WNPST. In addition, the results show that the patterns of anomalous lower‐tropospheric atmospheric baroclinicity and barotropic energy transfer do not match the EAWM‐related anomalous WNPST. The upper‐tropospheric jet anomalies may be related to the weakening in the peak area and the western flank of the climatological WNPST. The impact of the EAWM on the zonal movement of the WNPST can be related to the anomalous baroclinic energy transfer and buoyancy conversion. Furthermore, the moisture effect including anomalous meridional and vertical eddy moisture flux may also play a role by latent heat release.