Synoptic Climatology Research Articles

A synoptic climatology of rain-on-snow flooding in Mid-Atlantic region using NCEP/NCAR Re-Analysis

ABSTRACT Rain-on-snow (ROS) flooding is common throughout the Appalachians and Mid-Atlantic region primarily during late winter and spring. Six recent (2007–2013) widespread snowmelt-related flood events throughout Pennsylvania and other Mid-Atlantic states are used to gain an understanding of synoptic-scale atmospheric conditions that generate annual maximum flows for the region. NCEP/NCAR Re-analysis output for six individual case studies and an all-event composite suggest similar synoptic-scale atmospheric conditions lead to widespread ROS flooding. Snow ablation and subsequent flooding are heavily influenced by the low-level (850 mb Low Level Jet) advection of warm, moist air from the Gulf of Mexico and Atlantic Ocean around an area of high pressure off the Atlantic Coast towards low pressure in the mid-continent. An anomalously deep 500mb trough in the mid-continent aids in steering heat and moisture into the study area. The sustained advection of warm, moist air into the region allows for the snowpack to first ripen and then ablate, thus producing widespread ROS flooding throughout the study area. Although regional snowpack ablation combined with liquid precipitation drive ROS flooding, the impact of antecedent soil moisture or frozen ground should not be overlooked. New information presented herein provides flood forecasters identifiable synoptic-scale features that may precede ROS flooding.

Synoptic climatology of nuisance flooding along the Atlantic and Gulf of Mexico coasts, USA

Nuisance flooding (NF; also known as high-tide, or “sunny day” flooding) is an increasingly prevalent phenomenon afflicting coastal developments worldwide. NF often results when high tides, exacerbated by global sea level rise, coincide with onshore-directed surface winds. The elevated tidal condition, compounded by frictionally forced ocean currents, then inundates coastal infrastructure, posing a non-life-threatening inconvenience for local residents. Even though NF events are formed by a coupling of atmospheric and oceanic conditions, the large-scale atmospheric circulations favorable for NF have received little attention. Using a 40 year NF database derived from coastal gauge data, this study identifies the mid-tropospheric synoptic atmospheric patterns within days of NF events along the Atlantic and Gulf of Mexico coasts of the USA. ERA-Interim reanalysis supplies 500 hPa geopotential height patterns over North America that coincide with NF events. Subsequently, a principal components analysis is performed upon all NF-associated 500 hPa patterns, disaggregated by region (New England, Mid-Atlantic, and Gulf Coast), to identify dominant intra-variability NF-related circulations. Consistent with prior work, results show that NF frequency is increasing with time. Further, each region is characterized by a unique set of dominant NF synoptic patterns. Most patterns have clear physical associations to NF mechanisms, such as a nearby 500 hPa trough that would support a surface cyclone and strong onshore surface winds, or a mid-level high-pressure cell that would direct onshore-oriented return flow along its western periphery. However, some patterns correspond less obviously to oft-referenced NF mechanisms and may instead reflect low-frequency modes of variability and/or localized influences.

Synoptic climatology of supercell‐type tornado and very large hail days in Turkey

Synoptic climatology of supercell‐type tornado and very large hail days in Turkey

An Updated Synoptic Climatology of Lake Erie and Lake Ontario Heavy Lake-Effect Snow Events

Lake-effect snow (LES) storms pose numerous hazards, including extreme snowfall and blizzard conditions, and insight into the large-scale precursor conditions associated with LES can aid local forecasters and potentially allow risks to be mitigated. In this study, a synoptic climatology of severe LES events over Lakes Erie and Ontario was created using an updated methodology based on previous studies with similar research objectives. Principal component analysis (PCA) coupled with cluster analysis (CA) was performed on a case set of LES events from a study domain encompassing both lakes, grouping LES events with similar spatial characteristics into the primary composite structures for LES. Synoptic scale composites were constructed for each cluster using the North American Regional Reanalysis (NARR). Additionally, one case from each cluster was simulated using the Weather Research and Forecast (WRF) model to analyze mesoscale conditions associated with each of the clusters. Three synoptic setups were identified that consisted of discrepancies, mostly in the surface fields, from a common pattern previously identified as being conducive to LES, which features a dipole and upper-level low pressure anomaly located near the Hudson Bay. Mesoscale conditions associated with each composite support differing LES impacts constrained to individual lakes or a combination of both.

A Synoptic Climatology of Spring Dryline Convection in the Southern Great Plains

AbstractA dataset of drylines within a region of the southern Great Plains was constructed to investigate the large-scale environments associated with the initiation of deep moist convection. Drylines were identified using NOAA/NWS Weather Prediction Center surface analyses for all April, May, and June days 2006–15. Doppler radar and visible and infrared satellite imagery were used to identify convective drylines, where deep, moist convection was deemed to have been associated with the dryline circulation. Approximately 60% of drylines were convective, with initiation most frequently occurring between 2000 and 2100 UTC. Composite synoptic analyses were created of 179 convective and 104 nonconvective dryline days. The composites featured an upper-level long-wave trough to the west of the Rockies and a ridge extending across the northern and eastern United States. At the surface, the composites featured a broad surface cyclone over western Texas and southerly flow over the south-central states. Convective drylines featured more amplified upper-level flow, associated with a deeper trough in the western United States and a stronger downstream ridge than nonconvective drylines up to 5 days preceding a dryline event. By the day of a dryline event, the convective composite features greater low-level specific humidity and higher CAPE than the nonconvective composite. These results demonstrate that synoptic-scale processes over several days help create conditions conducive to deep, moist convection along the dryline.

Drought reconstruction based on tree-ring earlywood of Picea obovata Ledeb. for the southern Altay Mountains

ABSTRACT In this study, a 177-year April–June Palmer Drought Severity Index (PDSI) for the southern slopes of the Altay Mountains (China) was reconstructed based on the earlywood width of 96 Siberian spruce (Picea obovata Ledeb.) samples located at eight different sites. The reconstructed PDSI tracked the observed data well (r = 0.723, p < .0001, n = 52). This PDSI reconstruction captures some drought years and periods noted in historical documents, and it agrees well with other hydroclimatic reconstructions for the surrounding area. The 22-, 11-, 2.3-, and 2.1-year cycles of the reconstruction and the spatial correlation with sea surface temperature revealed that the variability of the PDSI for the study area might be influenced by both the Schwabe cycle of solar activity and the interannual oscillation of land–atmosphere–ocean circulation systems. Spatial correlation also showed the reconstruction contained climatic signals, being representative of a larger area extending from northern Xinjiang to northeastern Kazakhstan and a part of southern Russia. Synoptic climatology analysis revealed a relationship between anomalous atmospheric circulation and wet/dry years on the southern slopes of the Altay Mountains in China and its surrounding area.

A 475-year tree-ring-width record of streamflow for the Qingshui River originating in the southern slope of the central Tianshan Mountains, China

ABSTRACT We reconstructed the streamflow of the Qingshui River, which originates from the southern slopes of the central Tianshan Mountains in western China. The correlation between the hydrometeorological data and the tree-ring chronology indicated that the influences of temperature and precipitation on the radial growth of spruces were contrary in the different periods of the growth and non-growth seasons, while the highest correlation was found between the streamflow and the chronology. Based on the results of correlation analyses, a 475-year streamflow reconstruction from the previous August to the current July for the Qingshui River was reconstructed using the regional chronology. The reconstructed streamflow series matched observations well, with 43.1% of the variation in the observed streamflow. The streamflow reconstruction had a significantly positive correlation with a gridded PDSI dataset for an area closely corresponding to the Qingshui River watershed. The 50- and 2.0–3.0-year cycles of this reconstruction were consistent with other tree-ring based hydrometeorological reconstructions, and revealed the possible influences of the Gleissberg solar activity cycle and the interannual oscillations of land–atmospheric–ocean systems. The streamflow reconstruction for the Qingshui River captures some wet/drought years noted in historical documents and two turbulent periods after 1700 in Xinjiang, and agrees well with the streamflow reconstruction for the Kaidu River. Synoptic climatology analysis revealed a relationship between anomalous atmospheric circulation and wet/dry years for the Qingshui River watershed and its surrounding area. It is likely that the path of moisture in the wet years mainly originates from the Indian Ocean.

A Synoptic Climatological Analysis of the Atmospheric Drivers of Water Clarity Variability in the Great Lakes

AbstractA historical water clarity index (Kd index or KDI) was developed through the use of satellite-derived and validated diffuse light attenuation (Kd; m−1) for each of the Great Lakes (and subbasins) on a daily level from 1998 to 2015. A statistical regionalization was performed with monthly level KDI using k-means clustering to subdivide the Great Lakes into regions with similar temporal variability in water clarity. The KDI was then used to assess the relationship between water clarity and atmospheric circulation patterns and stream discharge. An artificial neural-network-based self-organized map data reduction technique was used to classify atmospheric patterns using four atmospheric variables: mean sea level pressure, 500-hPa geopotential heights, zonal and meridional components of the wind at 10 m, and 850-hPa temperature. Stream discharge was found to have the strongest relationship with KDI, suggesting that sediments and dissolved matter from land runoffs are the key factors linking the atmosphere to water clarity in the Great Lakes. Although generally lower in magnitude than stream discharge, atmospheric circulation patterns associated with increased precipitation tended to have stronger positive correlations with KDI. With no long-range forecasts of stream discharge, the strong relationship between atmospheric circulation patterns and stream discharge may provide an avenue to more accurately model water clarity on a subseasonal-to-seasonal time scale.

Weather Patterns Associated with Pain in Chronic-Pain Sufferers

AbstractThe belief that weather influences people’s health has been prevalent for millennia. Recent studies on the relationship between weather and pain for those who suffer from chronic pain remain indeterminate, with some studies finding strong effects and others finding no effects; most studies face limitations to their study design or dataset size. To address these limitations, a U.K.-wide smartphone study Cloudy with a Chance of Pain was conducted over 15 months with 10,584 citizen scientists who suffer from chronic pain, producing the largest dataset both in duration and number of participants. Compared to other similar citizen-science studies, our retention of participants was substantially better, with 15% still entering data nearly every day after 200 days. Analysis of the dataset using synoptic climatology and compositing revealed the daily weather associated with a prevalence of high pain and low pain across the population. Specifically, our results indicate that the top 10% of days with a high percentage of participants (about 20%) experiencing a pain event (represented here by a +1 change or greater in their pain level on a 5-point scale; referred to as a high-pain day) were associated with below-normal pressure, above-normal humidity, higher precipitation rate, and stronger wind. In contrast, the bottom 10% of days with a small percentage of participants (about 10%) experiencing a pain event (a low-pain day) were associated with above-normal pressure, below-normal humidity, lower precipitation rate, and weaker wind. Thus, these synoptic weather patterns support the beliefs of many participants who said that low pressure—and its accompanying weather—was associated with a pain event.

A synoptic climatology of potential seiche‐inducing winds in a large intermontane lake: Quesnel Lake, British Columbia, Canada

AbstractExcitation of basin‐scale, internal waves (i.e., internal seiches) in lakes require spatially homogeneous wind fields that vary on time scales comparable to the seiche period, which can be on the order of several days in large lakes. We evaluate 2 years (October 1, 2016 to September 30, 2018) of 15‐min wind data from a shore‐based meteorological station to identify strong wind episodes likely to excite internal seiches in a large and geometrically complex lake surrounded by convoluted topography, Quesnel Lake, British Columbia, Canada. Our findings include the identification of strong wind event seasonality, with peak mean monthly wind speeds in April and November, and minimum mean monthly wind speeds in August. Using geopotential heights (GPHs) from 1.5° × 1.5° gridded reanalysis data to reconstruct the atmospheric state for each strong wind episode, two primary synoptic patterns are identified that, in conjunction with local topographic channelling, lead to either easterlies or westerlies occurring at our sampling station, with strong easterly episodes three times more frequent than westerly episodes. This highlights the important role that developing low‐pressure systems in the Northeastern Pacific Basin have in setting up the GPH gradient required for persistent strong winds at Quesnel Lake, in the hours and days before these storms make landfall. The projection of synoptic patterns of strong wind events onto a 4 × 3 self‐organizing map clustered strong wind events by mean wind direction, similar to the results of a manual classification. Methods to identify the strong wind episodes and the resulting self‐organizing map are both evaluated in‐part by two case studies where strong winds are known to have excited a basin‐scale baroclinic response in Quesnel Lake.

Reconstructing summer upper-level flow in the northern Rocky Mountains using an alpine larch tree-ring chronology

Mid-latitude mesoscale weather during the climatological summer is strongly influenced by fluctuations in synoptic-scale circulation patterns. Previous research has linked Arctic amplification to alterations in summer synoptic climatology, leading to more extreme weather events in the mid-latitudes. In this study, seasonal (JJA) upper-level (500 hPa) atmospheric flow is reconstructed in the mid-latitudes using an alpine larch Larix lyallii Parl. tree-ring chronology sampled from western Montana. Significant relationships were found between alpine larch radial growth and upper-level flow patterns derived from the North American Regional Reanalysis dataset (1979-2015). Meridional and zonal flows that manifest in ridging are associated with enhanced radial growth of alpine larch (i.e. meridional flow west [r = 0.504, p = 0.001] and zonal flow north [r = 0.642, p &lt; 0.001] of the study site). Meridional and zonal flows associated with troughing result in decreased radial growth (i.e. meridional flow east [r = -0.497, p = 0.001] and zonal flow south [r = -0.584, p &lt; 0.001] of the study site). Using the leave-one-out method, a linear regression model was calibrated and verified between a principal component analysis score derived from measurements of upper-level flow in western North America and alpine larch tree growth. The 444 yr climate reconstruction of summer 500 hPa flow suggests that ridging is becoming more intense over the western United States and Canada since the 1980s.

Identifying patterns of airborne pollen distribution using a synoptic climatology approach

Understanding the mechanisms of pollen release and dispersion in the atmosphere is of high importance, not only for getting an insight on the patterns of movement of these biological particles that are necessary for plants' reproduction, but also because exposure to airborne pollen is a major concern for respiratory allergies worldwide. In this work, a synoptic circulation-to-environment classification method was adopted to elucidate the relationship between distinct atmospheric patterns and pollen levels for the 11 most abundant but also allergenic taxa in Thessaloniki, Greece, for the 15-year period 1987–2001. It was found that the NW1 depressional weather type is associated with the “low winter pollen season” and high levels of pollen from Carpinus spp., Corylus spp., Cupressaceae, Platanus spp., Pinaceae, Quercus spp. and Urticaceae. In contrast, the SW1 cyclonic type is linked to the “high spring-summer pollen season” and high levels of pollen from Oleaceae and Urticaceae. On the other hand, anticyclonic weather is associated with the “summer-autumn pollen season” and high levels of Poaceae and Chenopodiaceae pollen in the atmosphere. Regional transport of Alnus pollen is linked to a strong high-pressure system centered over Italy, giving light NE winds over northern Greece. These findings shed light to the synoptic climatology of airborne pollen in Thessaloniki and could feed early-warning systems for alerting vulnerable groups of the allergic population.

Drylines in Argentina: Synoptic Climatology and Processes Leading to Their Genesis

Abstract Drylines have been identified as relevant synoptic-scale phenomena that frequently occur in several regions around the world. Despite previous works and the experience of local forecasters that recognizes the occurrence of drylines in Argentina and suggests its possible association with convection initiation, knowledge about the mechanisms leading to the genesis of these features is poor. This paper presents the first synoptic climatology of these drylines as well as a first approach to the understanding of the processes leading to their formation. The climatology is based on an automated algorithm for dryline identification applied to reanalysis data. We found that drylines are more frequent between the northern Patagonia plateau and the central Argentinean plains. A composite analysis is performed to analyze the processes leading to the formation of synoptic-scale drylines within this region. It was found that these drylines form in the confluence between a warm and moist air mass driven by a northwesterly flow and drier air flowing east over the northern Patagonia plateau. The dry air originates on top of the Pacific maritime boundary layer and experiences lee subsidence after crossing the Andes range creating an area of dry and warm air that is advected to the east by the westerly synoptic-scale flow, and transported downward during the day due to strong boundary layer turbulence. At the same time, surface heating over the plateau leads to substantial warming of the originally colder dry air behind the dryline, thus reversing the horizontal temperature gradient across the dryline.

Monthly and seasonal variability of dust events over northern Saudi Arabia

AbstractThe monthly and seasonal variability and distribution of dust events over northern Saudi Arabia were studied using ground‐based measurements from 11 surface stations for the period of 1978–2010. Additionally, to study the synoptic climatology of the dust variability, the aerosol index (AI) data from the Total Ozone Mapping Spectrometer (TOMS) satellite and meteorological data from the National Center for Environmental Prediction and National Center for Atmospheric Research (NCEP/NCAR) reanalysis datasets were used. The dust types observed at the surface stations are classified into two categories: weak dust and dust storms. A statistical study of the ground measurements demonstrated that weak dust category events are prevalent in the cold months, whereas storm category events are prevalent in the hot months. Additionally, the annual distribution distinguishes two periods for dust observations, before and after 1989, where the number of events in the first period is lower than the annual average but increases during the second period. The synoptic climate study indicated that two main atmospheric wind patterns, anticyclonic and northerly (shamal) patterns, accompany the dust events in the study area. The dust in winter and autumn is mainly affected by the anticyclonic pattern, while that in spring and summer is mainly affected by the shamal pattern. In addition, a synoptic study of selected cases confirmed the climate results and demonstrated the existence of two atmospheric patterns corresponding to winter and summer. Both patterns include troughs over the Red Sea and Arabian Gulf and a ridge or high‐pressure cell over the eastern Mediterranean region during the summer atmospheric pattern and over the mid‐Arabian Peninsula during the winter atmospheric pattern. The characteristic of non‐dust storm composition demonstrated that the storms exhibit pronounced synoptic systems (winter and summer) with the highest pressure/geopotential gradient near the Arabian Peninsula.

Comparing daily temperature averaging methods: the role of synoptic climatology in determining spatial and seasonal variability

ABSTRACTThe two primary methods for averaging daily near-surface air temperature are twice-daily averaging (i.e., the sum of the maximum and minimum divided by two) and hourly averaging (i.e., using the 24 hourly values of a day). To quantify the influence of synoptic (air mass) climatology on the numerical difference between the two types of daily temperature averaging, a synoptic climatology for 215 weather stations across the Contiguous United States (CONUS) was developed for the period 1981–2010 and then correlated with those difference values. A significant correlation is found between air mass frequency and the temperature difference, especially during the non-transition seasons (i.e., summer and winter). This pattern is due to the influence of air mass type on the shape of the daily temperature curve. The correlation results also show spatial variability, as air masses that are more frequent in the northern CONUS (e.g., Dry Polar) influence the diurnal temperature curve differently than air masses more common in the southern CONUS (e.g., Moist Tropical). Future work can capitalize on these results by investigating different geographic regions and utilizing this correlation-based approach to analyze how anticipated future changes in the synoptic climatology of air masses influence the diurnal temperature curve.

Synoptic climatology of tropical and subtropical South America and adjoining seas as inferred from Geostationary Operational Environmental Satellite imagery

AbstractThree‐hourly infrared, visible and water vapour channel satellite imagery from the Geostationary Operational Environmental Satellite for the 15‐year period 2003–2017 is processed to obtain a climatology for the South American region. All major features such as the Intertropical Convergence Zones, the South Atlantic Convergence Zone, the Amazon Basin convection, the Atacama Desert and the Northeast Brazil semiarid region are well delineated. Seasonal migrations and shifts of cloud systems are obtained. The study reveals the precise locations and extents of convective regions associated with large scale permanent and semi‐permanent features. The double Intertropical Convergence Zone in eastern equatorial Pacific is discussed. Some hitherto unnoticed and little discussed features such as the coastal cloud inhibition near the southeastern Brazil region and a conspicuous convective region near the coast of the state of Para are found. The dynamical reasons for the formation of these features are postulated. This climatology should serve to validate different climate‐scenario models and Numerical Weather Prediction models, besides providing guidance to operational meteorologists of the region.

Modeling Ash Dispersal From Future Eruptions of Taupo Supervolcano

AbstractHazard analysis at caldera volcanoes is challenging due to the wide range of eruptive and environmental conditions that can plausibly occur during renewed activity. Taupo volcano, New Zealand, is a frequently active and productive rhyolitic caldera volcano that has hosted the world's youngest known supereruption and numerous smaller explosive events. To assess ashfall hazard from future eruptions, we have simulated atmospheric ash dispersal using the Ash3d model. We consider five eruption scenarios spanning magma volumes of 0.1–500 km3 and investigate the main factors governing ash dispersal in modern atmospheric conditions. Our results are examined in the context of regional synoptic weather patterns (Kidson types) that provide a framework for assessing the variability of ashfall distribution in different wind fields. For the smallest eruptions (~0.1‐km3 magma), ashfall thicknesses &gt;1 cm are largely confined to the central North Island, with dispersal controlled by day‐to‐day weather and the dominance of westerly winds. With increasing eruptive volume (1–5‐km3 magma), ashfall thicknesses &gt;1 cm would likely reach major population centers throughout the North Island. Dispersal is less dependent on weather patterns as the formation of a radially expanding umbrella cloud forces ash upwind or crosswind, although strong stratospheric winds significantly restrict umbrella spreading. For large eruptions (50–500‐km3 magma), powerful expansion of the umbrella cloud results in widespread ashfall at damaging thicknesses (&gt;10 cm) across most of the North Island and top of the South Island. Synoptic climatology may prove a useful additional technique for long‐term hazard planning at caldera volcanoes.

The Impact of Atmospheric Circulation on Air Temperature Rise in Estonia

In comparison to the global average, the climate in the Baltic Sea region, including in Estonia, has warmed up particularly fast. From synoptic climatology's point of view, a question can be posed: is this warming caused by changes in the frequency of particular circulation types or warmer weather started accompanying these types? The main aim of present study is to analyze the relationship between increase of air temperature and changes in atmospheric circulation during the period of 1966-2015. Changes in the frequency of circulation types belonging to 12 classifications from COST733 data set and changes in accompanying air temperature were analyzed. The circulation types were divided into 'warm' and 'cold' for a given season according to daily temperature anomalies in three Estonian meteorological stations. On the basis of the similar air flow direction circulation types from different classifications were selected for intercomparison. Linear trend analysis showed that there were only a few statistically significant (p<0.05) changes in the frequency of circulation types. The major changes occurred in spring – the frequency of eastern and northeastern flow types has decreased, and the frequency of types related to northwestern flow has increased. However, the positive temperature anomalies have increased for practically all circulation types. A particularly great warming has taken place in winter 'cold' types. In conclusion, the increase of Estonian air temperature during the analyzed period is more likely associated with the changes of temperature within circulation types than of their frequency.

Synoptic Climatology of Rain-on-Snow Events in Alaska

Abstract Rain-on-snow (ROS) events can have adverse impacts on high-latitude ungulate populations when rain freezes in the snowpack, forming ice layers that block access to winter forage. In extreme cases, ROS events have led to mass die-offs. ROS events are linked to advection of warm and moist air, associated with extratropical cyclones. However, these conditions are common to many winter precipitation events, challenging our understanding of the particular conditions under which ROS events occur. This study uses the Modern-Era Retrospective Analysis for Research and Applications version 2 (MERRA-2) to differentiate ROS events in Alaska from precipitation events in which only snow falls on a preexisting snowpack [snow-on-snow (SOS)]. Over the North Slope and Kotzebue Sound, no clear difference exists between the tracks of ROS-producing and SOS-producing storms. However, in the interior, southwest, and Anchorage, tracks of ROS-producing storms tend to be farther north and west than for SOS-producing storms. The northwest shift of ROS-producing storms is linked to the position of upper-tropospheric anticyclones in the eastern Gulf of Alaska during ROS events. ROS-producing storms are no more intense than SOS-producing storms, but their association with atmospheric blocking leads to stronger pressure gradients on the east side of storms and thereby stronger advection of positive anomalies in temperature and precipitable water. For several sites, sea level pressure in the eastern Gulf of Alaska is also significantly higher a few days prior to ROS events than prior to SOS events, further implicating atmospheric blocking as a facilitator and potential predictor of ROS events.

The History of Ideas of Downscaling—From Synoptic Dynamics and Spatial Interpolation

The history of ideas, which lead to the now matured concept of empirical downscaling, with various technical procedures, is rooted in two concepts, that of synoptic climatology and that of spatial interpolation in a phase space. In the former case, the basic idea is to estimate from a synoptic weather map the regional details, and to assemble these details into a regional climatology. In the other approach, a shortcut is made, in that samples of (monthly, seasonal or annual) large-scale dynamical statistics (i.e., climate) are linked to a sample of local statistics of some variables of interest.