Northern Hemisphere In January Research Articles

Climatology of quasi-2-day wave structure and variability at middle latitudes in the northern and southern hemispheres

Climatological structure of the quasi-2-day wave (Q2DW) at middle latitudes in temperature and horizontal winds in the mesosphere and lower thermosphere (MLT) was compared between the northern and southern hemispheres. Determination of the Q2DW in temperature was based on observation data by the Microwave Limb Sounder (MLS) onboard NASA's Earth Observing System (EOS) Aura satellite over 17 years from August 2004 to May 2021 and the Q2DW in horizontal winds was derived from Aura/MLS geopotential height data using balance equations. Amplitudes were maximized in summer in the southern hemisphere and in the meridional wind in the northern hemisphere, but in winter in the zonal wind in the northern hemisphere. Summer amplitudes were larger in the meridional wind than the zonal wind in the southern hemisphere, but zonal amplitudes in winter were larger than meridional amplitudes in summer in the northern hemisphere. Westward propagating zonal wavenumber 3 (W3) was largest in both hemispheres, but in addition to well-known W4, W3, W2 and eastward propagating zonal wavenumber 2 (E2), we also found W1, zonally symmetric standing (S0), and E1. Eliassen-Palm fluxes were derived for each mode. W3, W2, W1, and E2 fluxes were exhibited upward and poleward in January in the southern hemisphere while only W3 fluxes were exhibited clearly upward and poleward in July in the northern hemisphere. The balance winds and radar winds agreed in both amplitude and phase in the southern hemisphere and at lower latitudes in the northern hemisphere in January, and at lower latitudes in both hemispheres in July. Furthermore, the Q2DW is modulation in amplitude and phase from the W3 by accumulating other modes.

Tropical African wildfire aerosols trigger teleconnections over mid-to-high latitudes of Northern Hemisphere in January

This study investigates the impacts of African wildfire aerosols (primary organic carbon, black carbon and sulfate) on the Northern Hemispheric in January. We found that wildfire aerosols emitted from equatorial Africa result in two mid-to-high latitudes atmospheric Rossby wave trains. One is from subtropical Atlantic propagating northeastward across Europe to Siberia, and the other one propagates eastward from Middle East across Asia to Pacific Northwest. The maximum positive geopotential height anomaly locates in Europe, concurrent with a greater-than-2 K land surface warming. These Rossby wave trains are excited by the atmospheric heating that caused by the wildfire aerosols in equatorial Africa and propagate into extratropics with the help of the westerly jet. Based on the diabatic heat budget analysis, the Rossby wave source is primarily from the solar absorption of black carbon of African wildfire. The present study emphasizes that wildfire aerosols, especial the absorbing aerosols, would have profound climate effects on remote regions and thus need more attentions.

Observations of the global haze redistribution on Titan from 2006 to 2015 with OSIRIS at Keck

We observed Titan with the OH Suppressing InfraRed Imaging Spectrograph (OSIRIS) at the W. M. Keck observatory from 2006 through 2015 using adaptive optics. The sunlight scattered by atmospheric haze was spatially resolved in the 2.0 µm (K) band window, and the spectra were analyzed with a radiative transfer model to determine the vertical (altitude) and meridional (latitudinal) variation in the haze distribution over this time period. This study complements recent work by Karkoschka (2016) in the season of observations, in the time span and sampling interval, in wavelength coverage and spectral resolution, as well as in the radiative transfer methodology and analysis. We observe the largest meridional gradient in haze opacity above 20 km toward the northern hemisphere in January 2010. Individual observations can show significant deviations from a relatively smooth linear gradient in haze across the entire disk. The variation in haze below 20 km is rarely well-described by a simple model and there is a systematically smaller amount of haze opacity retrieved from the equator to 10° S when observing the disk with a sub-observer longitude near 150° W. This correlation with longitude suggests one of the following; a localized decrease in haze scattering, a localized increase in gas opacity, or a systematic over-estimate of the surface albedo in this region.

Spatiotemporal analysis of the January Northern Hemisphere circumpolar vortex over the contiguous United States

AbstractJanuary 2014 will be remembered for the sensationalized media usage of the term “polar vortex” which coincided with several polar air outbreaks. A United States polar vortex (USPV) perspective is presented to better understand the January spatial and temporal variability of this regional component of the Northern Hemisphere circumpolar vortex. Use of the monthly mean 5460 m isohypse to represent the location of the USPV extent and area revealed that the spatial features of the January 2014 USPV were not extreme relative to certain 1948–2013 Januaries. Furthermore, the Arctic Oscillation (AO), Pacific‐North American (PNA) Pattern, and Pacific Decadal Oscillation (PDO) are all linked to southernmost latitude of the USPV trough, but the PDO and PNA are most closely associated with the longitude at which this latitude occurs. The AO is closely related to the area of the United States enclosed within the USPV.

Evaluation of the Surface Radiation Budget in the Atmospheric Component of the Hadley Centre Global Environmental Model (HadGEM1)

Abstract The partitioning of the earth radiation budget (ERB) between its atmosphere and surface components is of crucial interest in climate studies as it has a significant role in the oceanic and atmospheric general circulation. An analysis of the present-day climate simulation of the surface radiation budget in the atmospheric component of the new Hadley Centre Global Environmental Model version 1 (HadGEM1) is presented, and the simulations are assessed by comparing the results with fluxes derived from satellite data from the International Satellite Cloud Climatology Project (ISCCP) and ground measurements from the Baseline Surface Radiation Network (BSRN). Comparisons against radiative fluxes from satellite and ground observations show that the model tends to overestimate the surface incoming solar radiation (Ss,d). The model simulates Ss,d very well over the polar regions. Consistency in the comparisons against BSRN and ISCCP-FD suggests that the ISCCP-FD database is a good test for the performance of the surface downwelling solar radiation in climate model simulations. Overall, the simulation of downward longwave radiation is closer to observations than its shortwave counterpart. The model underestimates the downward longwave radiation with respect to BSRN measurements by 6.0 W m−2. Comparisons of land surface albedo from the model and estimates from the Moderate Resolution Imaging Spectroradiometer (MODIS) show that HadGEM1 overestimates the land surface albedo over deserts and over midlatitude landmasses in the Northern Hemisphere in January. Analysis of the seasonal cycle of the land surface albedo in different regions shows that the amplitude and phase of the seasonal cycle are not well represented in the model, although a more extensive validation needs to be carried out. Two decades of coupled model simulations of the twentieth-century climate are used to look into the model’s simulation of global dimming/brightening. The model results are in line with the conclusions of the studies that suggest that global dimming is far from being a uniform phenomenon across the globe.

Detection of external influence on trends of atmospheric storminess and northern oceans wave heights

The atmospheric storminess as inferred from geostrophic wind energy and ocean wave heights have increased in boreal winter over the past half century in the high-latitudes of the northern hemisphere (especially the northeast North Atlantic), and have decreased in more southerly northern latitudes. This study shows that these trend patterns contain a detectable response to anthropogenic and natural forcing combined. The effect of external influence is found to be strongest in the winter hemisphere, that is, in the northern hemisphere in January–March and in the southern hemisphere in July–September. However, the simulated response to anthropogenic and natural forcing combined, which was obtained directly from climate models in the case of geostrophic wind energy and indirectly via an empirical downscaling procedure in the case of ocean wave heights, is significantly weaker than the magnitude of the observed changes in these parameters.

Shifts of means are not a proxy for changes in extreme winter temperatures in climate projections

Changes in the severity of extreme weather events under the influence of the enhanced greenhouse effect could have disproportionally large effects compared to changes in the mean climate. Here, we explored the meteorological circumstances of extremes and changes therein using two 49-member climate model ensembles for reference (1961–1990) and scenario (2051–2080) greenhouse-gas concentrations. We have focused on daily-mean surface-air temperatures over the Northern Hemisphere in January. Over large parts of the continents, changes in the one-in-10-year temperature events are influenced at least as much by changes in the shape of the probability distribution functions (PDFs) as by shifts in the mean. In coastal areas, this is largely attributable to changes in the large-scale circulation, for those types of extremes linked to infrequent wind directions. In other areas, the inhomogeneous mean warming, increasing inland and polewards, affects the tails of the local temperature PDFs. Temperature extremes in widely different regions were found to be linked by a large-scale circulation anomaly pattern, which resembles the Arctic Oscillation. In the scenario ensemble, this anomaly pattern favors its positive phase, leading to enhanced probabilities of westerly winds in a belt around the Northern Hemisphere.

January northern hemisphere circumpolar vortex variability and its relationship with hemispheric temperature and regional teleconnections

Variability in the hemispheric-scale atmospheric circulation can be directly linked to variations in surface environmental features, such as temperature, precipitation, salinity of water bodies, and pollutant transport. One indicator of the behavior of the hemispheric-scale circulation is the circumpolar vortex (CPV). This research utilizes a geographic information system approach to characterize variability in the Northern Hemispheric (NH) CPV. Specifically, the area, shape, and centroid of the January NHCPV are analyzed for 1959–2001 because it may provide insight about relationships between hemispheric-scale circulation and global temperature change. We also use a new means of characterizing the hemispheric-scale circulation using a ‘circularity ratio’ (Rc). Results suggest that the January NHCPV has exhibited no long-term trends in area or shape, and that the mean centroid is positioned at approximately 85.3°N, 178.0°W. Regional patterns emerge, which suggest that the area and circularity are associated with variability in surface temperature and moist static energy. Furthermore, the area of the January NHCPV is associated with variability in the Arctic Oscillation, while the shape is tied to variability in the Pacific-North American teleconnection pattern. These results will facilitate understanding of the relationship between hemispheric-scale circulation, regional circulation, and local temperatures. Copyright © 2005 Royal Meteorological Society.

Impact of a Convectively Forced Gravity Wave Drag Parameterization in NCAR CCM3

A parameterization of gravity wave drag forced by subgrid-scale cumulus convection (GWDC) proposed by Chun and Baik is implemented into the National Center for Atmospheric Research Community Climate Model (NCAR CCM3) and its effect on perpetual January and July climate is investigated. The cloud-top gravity wave stress is concentrated in the intertropical convergence zone where persistent deep cumulus clouds exist. The resultant zonal wind acceleration due to the breaking of convectively forced gravity waves is predominantly found in the tropical lower stratosphere with westerly acceleration above cloud top and easterly acceleration just below it. Since the parameterized gravity waves are stationary relative to convective clouds, wave breaking occurs mainly in the tropical lower stratosphere where the zonal wind is weak enough for wave saturation. It is shown that the GWDC parameterization significantly alleviates the systematic model biases of zonal-mean zonal wind and temperature. In particular, excessive easterlies in the tropical stratosphere and excessive cold temperatures in the tropical lower stratosphere are reduced by more than 50% by including the GWDC parameterization. The horizontal wind divergence field in the tropical upper troposphere and lower stratosphere is also significantly improved with the GWDC parameterization. The impact of the GWDC parameterization extends to mid- to high latitudes through planetary wave activity in the winter hemisphere. The increased amplitude of zonal wavenumber 3 in the January Northern Hemisphere and the increased amplitude of zonal wavenumber 2 in the July Southern Hemisphere lead to significant improvements in model performance. The impact of the GWDC parameterization on Eliassen‐Palm (EP) flux divergence forcing by stationary waves is generally opposite to that by transient waves in the extratropics, especially in the Northern Hemisphere wintertime. Hence, the zonal-mean zonal wind change by the GWDC parameterization occurs mainly in the Tropics by direct gravity wave drag forcing.

Changing ozone and changing circulation in northern mid‐latitudes: Possible feedbacks?

The Met Office Unified Model including a simplified stratospheric chemistry scheme was used to perform three integrations each of twenty years to study the connection between changes in lower stratospheric ozone and the circulation. The model radiation scheme used 1) the ozone calculated by the model, 2) climatological zonal‐mean ozone derived from 1) and, 3) climatological zonal‐mean ozone with an imposed mid‐latitude ozone loss in the northern hemisphere in spring. Integrations 1) and 2) only differ significantly in the northern hemisphere in January, whereas the spring season is unaffected. The dynamical changes between 1)/2) and 3) are most obvious during March, the time of the strongest imposed loss, but the largest impact, on both dynamics and ozone, is found northwards and upwards from the region of the imposed mid‐latitude anomaly away from middle latitudes. We conclude that in our calculations the imposed (observed) middle latitude loss does not produce a large additional feedback on the ozone distribution.

Comparison of ER‐2 aircraft and POAM III, MLS, and SAGE II satellite measurements during SOLVE using traditional correlative analysis and trajectory hunting technique

We compared the version 5 Microwave Limb Sounder (MLS), version 3 Polar Ozone and Aerosol Measurement III (POAM III), version 6.0 Stratospheric Aerosol and Gas Experiment II (SAGE II), and NASA ER‐2 aircraft measurements made in the Northern Hemisphere in January–February 2000 during the SAGE III Ozone Loss and Validation Experiment (SOLVE). This study addresses one of the key scientific objectives of the SOLVE campaign, namely, to validate multiplatform satellite measurements made in the polar stratosphere during winter. This intercomparison was performed by using a traditional correlative analysis (TCA) and a trajectory hunting technique (THT). TCA compares profiles colocated within a chosen spatial‐temporal vicinity. Launching backward and forward trajectories from the points of measurement, the THT identifies air parcels sampled at least twice within a prescribed match criterion during the course of 5 days. We found that the ozone measurements made by these four instruments agree most of the time within ±10% in the stratosphere up to 1400 K (∼35 km). The water vapor measurements from POAM III and the ER‐2 Harvard Lyman α hygrometer and Jet Propulsion Laboratory laser hygrometer agree to within ±0.5 ppmv (or about ±10%) in the lower stratosphere above 380 K. The MLS and ER‐2 ClO measurements agree within their error bars for the TCA. The MLS and ER‐2 nitric acid measurements near 17‐ to 20‐km altitude agree within their uncertainties most of the time with a hint of a positive offset by MLS according to the TCA. We also applied the Atmospheric and Environmental Research, Inc. box model constrained by the ER‐2 measurements for analysis of the ClO and HNO3 measurements using the THT. We found that: (1) the model values of ClO are smaller by about 0.3–0.4 (0.2) ppbv below (above) 400 K than those by MLS and (2) the HNO3 comparison shows a positive offset of MLS values by ∼1 and 1–2 ppbv below 400 K and near 450 K, respectively. Our study shows that, with some limitations (like HNO3 comparison under polar stratospheric cloud conditions), the THT is a more powerful tool for validation studies than the TCA, making conclusions of the comparison statistically more robust.

Association between modes of variability of January Northern Hemisphere snow cover and circulation

An Empirical Orthogonal Function (EOF) analysis has been applied to NOAA/NESDIS snow concentration data. The major modes of variability in January Northern Hemisphere snow concentration have been extracted and analysed. The analysis was completed separately over Eurasia and North America. Strong, coherent patterns were found for each of the first three EOFs that were analysed over both continents. Over Eurasia the first EOF showed much of Europe as well as western and central Asia in phase but eastern Asia of the opposite phase although the signal was somewhat weaker. North America had a very similar first EOF with a large positive anomaly centered over Montana reaching loadings of over 0.8. East of the Great Lakes, the anomaly changes sign, although again, its magnitude is much smaller. An EOF examination was also made of the anomalous 700 hPa geopotential height fields. These modes of variability were correlated with those of snow cover with the aim of investigating the mechanisms by which the surface boundary snow and the overlying circulation can interact. The stronger correlations were discussed and logical physical scenarios were presented for each. The results indicate that there was no common pattern whereby one medium was always forcing the other but rather a complex array of interactions where each medium could influence the other. To support the physical basis of the relationships being depicted by the EOF study, a case study of January 1981 was made. The presence of intercontinental relationships was also investigated and such relations were strongly suggested. It was proposed that the large scale organisation of the atmosphere between the two continents could go some way to explaining these links in snow variability.

Size Variations and Long-Wave Circulation within the January Northern Hemisphere Circumpolar Vortex: 1946–89

Abstract The close association between size variations in the Northern Hemisphere circumpolar vortex and surface and middle-troposheric thermal characteristics makes vortex measurement a valuable tool in monitoring and understanding climate change. Unfortunately, as with most hemispheric circulation indices, measures of total vortex size offer little insight into regional changes in the vortex. Traditional approaches to vortex size calculation, which are based upon planimeter measurements on a polar stereographic projection, limit the ability to examine regional contributions to the total vortex and cannot be used to assess specific linkages between vortex expansion and contraction and the broader class of long wave circulation phenomena. Furthermore, because the scale of the polar stereographic projection varies from one latitude to another, interannual variations in planimeter vortex size measurements are influenced somewhat by the position of the vortex relative to the North Pole. Many of these problem...

The flux of water‐vapour due to the mean winds and the convergence of this flux over the Northern Hemisphere in January and July

The flux of water‐vapour due to the mean winds and the convergence of this flux over the Northern Hemisphere in January and July

The flux of water vapour due to the mean winds and the convergence of this flux over the Northern Hemisphere in January and July

AbstractCharts are presented showing the flux of water vapour due to the mean winds, based on the mean distribution of water vapour and the mean geostrophic winds, in January and July, over an area comprising most of the Northern Hemisphere.There is evidence that this flux approximates fairly well to the total flux of water vapour, but the divergence of this flux does not always approximate so well to the divergence of the total flux. Nevertheless, comparison with independent estimates of evaporation minus precipitation over the oceans suggests that the two divergences are at least of the same order of magnitude, and further comparison with published charts of the divergence of the total annual flux of water vapour suggests some degree of detailed correspondence.

Mean upper contour patterns of the northern hemisphere — the thermal‐synoptic view‐point

AbstractThe mean 500 mb contour patterns and 1,000‐500 mb thickness patterns for the northern hemisphere in January and July are examined. The orographic‐dynamical hypothesis advocated by Bolin (1950) is considered. A thermal‐synoptic explanation, resting mainly on the direct thermal effects of land and sea modified by baroclinic synoptic processes, is regarded as satisfactory.

Der Wärmehaushalt der Atmosphäre

The mean caloric balance of the atmosphere is represented by diagram No. 1, which shows the usual lay-out, but is filled in with new figures according to own calculations based uponS. Fritz's new value of the earth's albedo. Possibilities of exchange between the heat surplus of the earth's surface and the heat deficiency of the atmosphere and between differing spots of the same layer are discussed. Regarding the vertical pattern of heat sources and cold sources, it may be seen that in the humid climates (tropics and temperate zone) the lower troposphere receives considerable amounts of heat and the upper troposphere and lower stratosphere lose heat, while in arid regions (subtropics and the cold pole of the earth), the lower layer does not receive heat or even radiates it. For finding geographic differences in heat economy, the individual changes of temperature of the air may be used. A map of the heat balance of the northern hemisphere in January shows zones of warmth over the warm ocean currents and zones of cooling over the continents.