Two Winter Storms Encountered by Columbus in 1493 Near the Azores*

1941 ◽  
Vol 22 (8) ◽  
pp. 303-308 ◽  
Author(s):  
Charles F. Brooks
Keyword(s):  
Cold Front ◽  
Winter Storms ◽  
Severe Storms ◽  
Cold Fronts

Synopsis The two severe storms that overtook Columbus on the return portion of his first voyage, when examined in the light of modern frontal theory, do not appear to have been simple circular storms, as previously thought, but disturbances marked by well developed fronts. The centers of both passed north of Columbus; he apparently experienced the warm sectors of both. The February storm seems to have had two cold fronts, and the March one a very sharp cold front. Storms of both kinds have been observed in the same portion of the Atlantic in recent years.

scholarly journals A CloudSat–CALIPSO View of Cloud and Precipitation Properties across Cold Fronts over the Global Oceans

2015 ◽  
Vol 28 (17) ◽  
pp. 6743-6762 ◽  
Author(s):  
Catherine M. Naud ◽  
Derek J. Posselt ◽  
Susan C. van den Heever
Keyword(s):  
Large Scale ◽  
Cold Front ◽  
Conveyor Belt ◽  
Low Level ◽  
Scale Parameters ◽  
Convective Clouds ◽  
Cold Fronts ◽  
Surface Front ◽  
High Level ◽  
The Impact

Abstract The distribution of cloud and precipitation properties across oceanic extratropical cyclone cold fronts is examined using four years of combined CloudSat radar and CALIPSO lidar retrievals. The global annual mean cloud and precipitation distributions show that low-level clouds are ubiquitous in the postfrontal zone while higher-level cloud frequency and precipitation peak in the warm sector along the surface front. Increases in temperature and moisture within the cold front region are associated with larger high-level but lower mid-/low-level cloud frequencies and precipitation decreases in the cold sector. This behavior seems to be related to a shift from stratiform to convective clouds and precipitation. Stronger ascent in the warm conveyor belt tends to enhance cloudiness and precipitation across the cold front. A strong temperature contrast between the warm and cold sectors also encourages greater post-cold-frontal cloud occurrence. While the seasonal contrasts in environmental temperature, moisture, and ascent strength are enough to explain most of the variations in cloud and precipitation across cold fronts in both hemispheres, they do not fully explain the differences between Northern and Southern Hemisphere cold fronts. These differences are better explained when the impact of the contrast in temperature across the cold front is also considered. In addition, these large-scale parameters do not explain the relatively large frequency in springtime postfrontal precipitation.

scholarly journals Contrasting Hydrodynamic Responses to Atmospheric Systems with Different Scales: Impact of Cold Fronts vs. That of a Hurricane

2020 ◽  
Vol 8 (12) ◽  
pp. 979
Author(s):  
Wei Huang ◽  
Chunyan Li
Keyword(s):  
Water Level ◽  
Cold Front ◽  
Volume Transport ◽  
Water Volume ◽  
Cold Fronts ◽  
Barataria Bay ◽  
Before And After ◽  
Frequent Exchange ◽  
The Right ◽  
Mexico Coast

In this paper, subtidal responses of Barataria Bay to an atmospheric cold front in 2014 and Hurricane Barry of 2019 are studied. The cold fronts had shorter influencing periods (1 to 3 days), while Hurricane Barry had a much longer influencing period (about 1 week). Wind direction usually changes from southern quadrants to northern quadrants before and after a cold front’s passage. For a hurricane making its landfall at the norther Gulf of Mexico coast, wind variation is dependent on the location relative to the location of landfall. Consequently, water level usually reaches a trough after the maximum cold front wind usually; while after the maximum wind during a hurricane, water level mostly has a surge, especially on the right-hand side of the hurricane. Water level variation induced by Hurricane Barry is about 3 times of that induced by a cold front event. Water volume flux also shows differences under these two weather types: the volume transport during Hurricane Barry was 4 times of that during a cold front. On the other hand, cold front events are much more frequent (30–40 times a year), and they lead to more frequent exchange between Barataria Bay and the coastal ocean.

scholarly journals The Origin of Western European Warm-Season Prefrontal Convergence Lines

2016 ◽  
Vol 31 (5) ◽  
pp. 1417-1431 ◽  
Author(s):  
Johannes M. L. Dahl ◽  
Jannick Fischer
Keyword(s):  
Western Europe ◽  
Cold Front ◽  
Warm Season ◽  
Surface Velocity ◽  
Weather Research And Forecasting ◽  
Forecasting Model ◽  
Cold Fronts ◽  
Convergence Line ◽  
Ageostrophic Circulation ◽  
Q Vector

Abstract The authors investigate the origin of prefrontal, warm-season convergence lines over western Europe using the Weather Research and Forecasting Model. These lines form east of the cold front in the warm sector of an extratropical cyclone, and they are frequently the focus for convective development. It is shown that these lines are related to a low-level thermal ridge that accompanies the base of an elevated mixed layer (EML) plume generated over the Iberian Peninsula and northern Africa. Using Q-vector diagnostics, including the components that describe scalar and rotational quasigeostrophic frontogenesis, it is shown that the convergence line is associated with the rearrangement of the isentropes especially at the western periphery of the EML plume. The ascending branch of the resulting ageostrophic circulation coincides with the surface velocity convergence. The modeling results are supported by a 3-yr composite analysis of cold fronts with and without preceding convergence lines using NCEP–NCAR Reanalysis-1 data.

scholarly journals Atmospheric Cold Front-Generated Waves in the Coastal Louisiana

2020 ◽  
Vol 8 (11) ◽  
pp. 900
Author(s):  
Yuhan Cao ◽  
Chunyan Li ◽  
Changming Dong
Keyword(s):  
Wave Height ◽  
Significant Wave Height ◽  
Cold Front ◽  
Wave Spectrum ◽  
Low Frequency ◽  
Wave Direction ◽  
Significant Wave ◽  
Cold Fronts ◽  
Directional Wave ◽  
Coastal Louisiana

Atmospheric cold front-generated waves play an important role in the air–sea interaction and coastal water and sediment transports. In-situ observations from two offshore stations are used to investigate variations of directional waves in the coastal Louisiana. Hourly time series of significant wave height and peak wave period are examined for data from 2004, except for the summer time between May and August, when cold fronts are infrequent and weak. The intra-seasonal scale variations in the wavefield are significantly affected by the atmospheric cold frontal events. The wave fields and directional wave spectra induced by four selected cold front passages over the coastal Louisiana are discussed. It is found that significant wave height generated by cold fronts coming from the west change more quickly than that by other passing cold fronts. The peak wave direction rotates clockwise during the cold front events. The variability of the directional wave spectrum shows that the largest spectral density is distributed at low frequency in the postfrontal phase associated with migrating cyclones (MC storms) and arctic surges (AS storms).

The Variability of Cold Front Precipitation

1956 ◽  
Vol 37 (9) ◽  
pp. 447-453 ◽  
Author(s):  
James M. Austin ◽  
R. H. Blackmer
Keyword(s):  
Cold Front ◽  
Radar Data ◽  
Precipitation Variability ◽  
Precipitation Patterns ◽  
Cold Fronts ◽  
Negative Results ◽  
Precipitation Type

Radar data are utilized to describe the precipitation patterns with 30 summertime cold fronts in the vicinity of Cambridge, Massachusetts. An attempt to relate the precipitation type and coverage to synoptic parameters which can be obtained from the conventional meteorological charts yielded essentially negative results. Possible causes of the precipitation variability are discussed.

Observations and Photographs of a Cold Front Made from an Airplane

1948 ◽  
Vol 29 (6) ◽  
pp. 313-318 ◽  
Author(s):  
John H. Conover
Keyword(s):  
Cold Front ◽  
Temperature Inversion ◽  
Cold Fronts ◽  
Made In

The purpose of presenting the following diagrams and cloud photos made in connection with an airplane flight over and through a cold front is to show cloud formations associated with a weak cold front. Such information is lacking in textbooks where only the more severe cold fronts are portrayed. Over land the front here described was preceded by daytime cumulus, their tops rising as the front approached. Some pileus was observed above them where later on Ac cumulogenitus (cug) formed as the tops reached that level. The layer became solid over the position of the cold front at the surface, and there was an upward bulge into the temperature inversion found at 8,000 feet. Over the sea, remains of the Ac cug in the form of lenticulars were found farthest ahead of the front. It is important to note that all the clouds were found some distance above the frontal discontinuity, within the warm air. This was owing to the dryness of the warm air. Detailed observations from the surface were made at Blue Hill Observatory, near by, during the flight.

scholarly journals Numerical Study of Precipitation Core-Gap Structure along Cold Fronts

2007 ◽  
Vol 64 (7) ◽  
pp. 2355-2377 ◽  
Author(s):  
Masayuki Kawashima
Keyword(s):  
Thermal Stratification ◽  
Cold Front ◽  
Numerical Study ◽  
Leading Edge ◽  
Shear Instability ◽  
Vertical Shear ◽  
Horizontal Shear ◽  
Cold Fronts ◽  
Simulated Precipitation ◽  
Gap Structure

Abstract The mechanism responsible for the core-gap structure of precipitation along narrow cold-frontal rainbands (NCFRs) is investigated through analyses of idealized cloud-resolving simulations of cold fronts. The control simulation, in which the prefrontal thermal stratification is characterized by a weak convective instability at low levels with convective available potential energy (CAPE) of ∼60 J kg−1, reproduces the typical alongfront variability of observed NCFRs. The simulated NCFR is broken up into regularly spaced, ellipsoidal cores oriented at a clockwise angle to the cold front. While horizontal-shear instability (HSI) has frequently been proposed as a mechanism leading to the alongfront variability of NCFRs, no characteristic features of HSI are recognized in the simulated vertical vorticity field at the leading edge of the cold front. The alongfront variability in precipitation is attributed to the formation of a wavelike disturbance just above the leading edge of the cold front. The wave phase lines are oriented nearly perpendicular to the direction of mean vertical shear, with enhanced (suppressed) precipitation occurring at the wave updrafts (downdrafts). An analysis of the eddy kinetic energy budget indicates that the wavelike disturbance derives most of its energy from the mean vertical shear and the buoyancy. Sensitivity experiments reveal a systematic relationship between the alongfront variability of NCFRs and the stability of the prefrontal thermal stratification. Simulated precipitation cores remain essentially parallel to the cold front when the prefrontal environment is absolutely stable or almost neutral to surface parcel ascent. The typical alongfront variability of NCFRs is reproduced for weakly unstable environments with small amounts of CAPE (≤140 J kg−1). On the other hand, simulations with sufficiently unstable environments produce precipitation cores oriented counterclockwise to cold fronts.

A Climatology of Nocturnal Warming Events Associated with Cold-Frontal Passages in Oklahoma

2011 ◽  
Vol 50 (10) ◽  
pp. 2042-2061 ◽  
Author(s):  
Anita Nallapareddy ◽  
Alan Shapiro ◽  
Jonathan J. Gourley
Keyword(s):  
Spatial Analysis ◽  
Initial Temperature ◽  
Cold Front ◽  
Surface Wind ◽  
Temperature Inversion ◽  
Sudden Increase ◽  
Wind Speeds ◽  
Cold Fronts ◽  
Oklahoma Mesonet ◽  
Temperature Inversions

AbstractA sudden increase in temperature during the nighttime hours accompanies the passages of some cold fronts. In some cold front–associated warming events, the temperature can rise by as much as 10°C and can last from a few minutes to several hours. Previous studies suggest that these events are due to the downward transport of warmer air by the strong and gusty winds associated with the cold-frontal passages. In this study, a climatology of nocturnal warming events associated with cold fronts was created using 6 yr of Oklahoma Mesonetwork (Mesonet) data from 2003 to 2008. Nocturnal warming events associated with cold-frontal passages occurred surprisingly frequently across Oklahoma. Of the cold fronts observed in this study, 91.5% produced at least one warming event at an Oklahoma Mesonet station. The winter months accounted for the most events (37.9%), and the summer months accounted for the fewest (3.8%). When normalized by the monthly number of cold-frontal passages, the winter months still had the most number of warming events. The number of warming events increased rapidly from 2300 to 0200 UTC; thereafter, the number of events gradually decreased. A spatial analysis revealed that the frequency of warming events decreased markedly from west to east across the state. In contrast, the average magnitude of the warming increased from west to east. In contrast to control periods (associated with cold-frontal passages without nocturnal warming events), warming events were associated with weaker initial winds and stronger initial temperature inversions. Moreover, the nocturnal temperature inversion weakened more during warming events than during control periods and the surface wind speeds increased more during warming events than during control periods. These results are consistent with previous studies that suggest the warming events are due to the “mixing out” of the nocturnal temperature inversion.

scholarly journals Variability of Precipitation along Cold Fronts in Idealized Baroclinic Waves

2017 ◽  
Vol 145 (8) ◽  
pp. 2971-2992 ◽  
Author(s):  
Jesse Norris ◽  
Geraint Vaughan ◽  
David M. Schultz
Keyword(s):  
Roughness Length ◽  
Cold Front ◽  
Thermal Structure ◽  
Surface Wind ◽  
Three Dimensional ◽  
Lower Troposphere ◽  
Equation Model ◽  
Vertical Shear ◽  
Cold Fronts ◽  
The Difference

Precipitation patterns along cold fronts can exhibit a variety of morphologies including narrow cold-frontal rainbands and core-and-gap structures. A three-dimensional primitive equation model is used to investigate alongfront variability of precipitation in an idealized baroclinic wave. Along the poleward part of the cold front, a narrow line of precipitation develops. Along the equatorward part of the cold front, precipitation cores and gaps form. The difference between the two evolutions is due to differences in the orientation of vertical shear near the front in the lower troposphere: at the poleward end the along-frontal shear is dominant and the front is in near-thermal wind balance, while at the equatorward end the cross-frontal shear is almost as large. At the poleward end, the thermal structure remains erect with the front well defined up to the midtroposphere, hence updrafts remain erect and precipitation falls in a continuous line along the front. At the equatorward end, the cores form as undulations appear in both the prefrontal and postfrontal lighter precipitation, associated with vorticity maxima moving along the front on either side. Cross-frontal winds aloft tilt updrafts, so that some precipitation falls ahead of the surface cold front, forming the cores. Sensitivity simulations are also presented in which SST and roughness length are varied between simulations. Larger SST reduces cross-frontal winds aloft and leads to a more continuous rainband. Larger roughness length destroys the surface wind shift and thermal gradient, allowing mesovortices to dominate the precipitation distribution, leading to distinctive and irregularly shaped, quasi-regularly spaced precipitation maxima.

scholarly journals Modeling the effects of cold front passages on the heat fluxes and thermal structure of a tropical hydroelectric reservoir

2013 ◽  
Vol 10 (7) ◽  
pp. 8467-8502 ◽  
Author(s):  
M. P. Curtarelli ◽  
E. H. Alcântara ◽  
C. D. Rennó ◽  
J. L. Stech
Keyword(s):  
Heat Loss ◽  
Weather Forecasting ◽  
Cold Front ◽  
Thermal Structure ◽  
Three Dimensional ◽  
Cumulative Effect ◽  
High Heat ◽  
Heat Fluxes ◽  
Tropical Reservoir ◽  
Cold Fronts

Abstract. We study the influence of cold fronts on the heat fluxes and thermal structure of a tropical reservoir located in Brazil. The period chosen for this study consisted of 49 days between 28 April 2010 and 15 July 2010 and was defined based on information from the Brazilian Centre for Weather Forecasting and Climate Studies (CPTEC), data collected in situ and the interpretation of remotely sensed images. During the selected time period, five cold front passages were identified, allowing us to analyze the cumulative effect of cold fronts and the reservoir's resilience on the days that elapsed between the passages. To better understand the physical processes that drive changes in heat fluxes and thermal structure, a simulation was performed that utilized a three-dimensional hydrodynamic model. The results showed that during the cold front days, the sensible and latent heat fluxes were enhanced by approximately 24% and 19%, respectively. The daily average heat loss was up to 167% higher on the cold front days than on the non-cold front days. The high heat loss and the increased wind intensity that occurred during the cold front passages destabilized the water column and provided partial or complete mixing. The colder waters of the Paranaíba River contributed to reestablish the thermal stratification following the passages of the cold fronts. These results suggest that cold front passages play an important role in the stratification and mixing regimes of Brazilian reservoirs located in southern and southeastern regions.

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