En sammanställning av en databas av inversionsdata från sonderingarna från Bromma under 1990 har utförts. I denna databas lagrades datum, tid, marktemperatur, marktryck samt tryck och temperatur för basen och toppen av upp till tre inversioner. Därur kunde sedan höjder till tryckytorna och temperaturdifferenser mellan topp och botten beräknas. En statistisk undersökning av materialet utfördes med avseende på höjden till inversionsbasen och temperaturökningen i inversionsskiktet. Även temperaturgradienten för inversionsskiktet studerades. Resultaten sammankopplades med den aktuella synoptiska situationen för att kunna förklara inversionernas fördelning i tid och rum. För att få en uppfattning om signifikansen av undersökningen gjordes en jämförelse med tillämpliga delar av en tysk undersökning gjord av Gutsche 1983. Resultaten visade en skillnad mellan sommar- och vinterhalvåret vad gäller fördelningen av inversioner över dygnet. Under sommaren förekom inversioner mycket oftare på natten än på dagen medan den skillnaden under vintern var betydligt mindre. Dessutom framkom att de flesta inversioner finns i de marknära skikten och i allmänhet har en liten temperaturökning från bas till topp. Vädersituationen under 1990 samt luckor i materialet gör dock att man ej bör dra alltför långtgående slutsatser av resultaten. / <p>Examensarbete F1 om 7 p (10,5 hp)</p>

I detta arbete har vindförhållandena på Utlängan, Ungskär och Ölands södra grund studerats. För att göra detta har synop-data från SMHI:s stationer på Ungskär och Ölands södra grund för tidsperioden 900801-911130 använts. Dessutom har data från en mast som stod uppställd på Utlängans södra udde under delar av -90 och -91 samt ett 50-tal enkelviseringar, utförda på Utlängans östra sida under perioden 910324-910614, använts. En vindmodell har använts för att räkna upp vinden till höjder högre än mätningarna (upp till 125 m). Denna modell användes också för att på data från masten beräkna vinden på viseringsplatsen. Genom att jämföra de modellberäknade vindarna med viseringsprofilerna kunde pilotballongernas stighastighet korrigeras och därmed erhölls en riktigare vindprofil från viseringarna. Modellen hade även möjlighet att korrigera för den ändring av vinden som en skrovlighetsförändring ger. Indata måste då vara — förutom vinden på en nivå, temperaturen på två nivåer, mäthöjder och z0 (vilka är de huvudsakliga inparametrarna till denna modell) — avståndet till skrovlighetsförändringen och dess art. Detta utnyttjades vid beräkningen av vinden för viseringsplatsen. För Ungskär och Ölands södra grund fanns bara en temperatur, varför två olika varianter av vindmodellen fick användas. På Ölands södra grund utnyttjades vattentemperaturen och för Ungskär bestämdes stabilitetsparametern 1/L genom att använda Turnerklassificering, vilken utnyttjar solhöjd, molnmängd och molnhöjd. Med hjälp av viseringsprofilerna har low-level jets studerats. Av de 52 viseringarna kunde ett — mer eller mindre utpräglat — vindmaximum ses i 27 av fallen. Drygt hälften av dessa hade ett tydligt maximum. Jämförelser mellan viseringsprofiler och modellberäknade vindar — för de övriga platserna — visade på att modellen gav för låga vindhastigheter runt 100 m:s höjd. Detta kan, åtminstone delvis, förklaras av att modellen ej tar hänsyn till low-level jets. En jämförelse mellan Ungskär och Ölands södra grund, för tidsperioden 900801-911130, gav högre vindhastigheter på Ölands södra grund (10,2 m/s mot 9,3 m/s på 125 m:s höjd) medan vindriktningsfördelningen var ungefär densamma. Även en jämförelse mellan Ungskär och masten på Utlängan, med uppmätta värden för de tidsperioder då samtidiga data fanns, gjordes. Resultaten från den gav lägre vindhastigheter på Utlängan än Ungskär (6,8 m/s mot 7,2 m/s på ca 14 m:s höjd) och en något annorlunda vindriktningsfördelning, vilket antyder lokal påverkan på vindhastighet och riktning. / <p>Examensarbete F1 om 7 p (10,5 hp)</p>

Efter stora påtryckningar från skandinaviskt håll genomfördes i början av 1970-talet ett sameuropeiskt mätprojekt för att klargöra huruvida svavelutsläpp i exempelvis Storbritannien påverkade försurningen av sjöar i Skandinavien. Elva västeuropeiska länder deltog i projektet – kallat LRTAP – vars mätningar pågick under åren 1972–1975. Dessa mätningar bekräftade de teorier som drivit fram projektet – att luftföroreningar (i detta fall svavelföreningar) kan transporteras långa vägar i atmosfären för att sedan deponeras i ett område långtifrån källan. Därigenom kom de fram till att ett land inte kan påverka depositionen inom landet till 100% genom egna restriktioner. Ett följdprojekt startades därför för att förse de olika ländernas regeringar med information om svavelutsläpp och svaveldeposition i de olika länderna. Ett mål uppsattes angående utsläppen – att 1993 inte släppa ut mer än 70% av 1980-års nivå – vilket tycks vara uppnåeligt. I Sverige har svavelutsläppen minskat från drygt 400 kton S/år i början av 1970-talet till 102 kton 1990, en reducering på ca 75%. Depositionen har dock inte minskat lika mycket, eftersom mängden svavel från Mellaneuropa fortfarande är stor. I Sverige är därför svaveldepositionen starkast koncentrerad i de sydvästra delarna och avtar sedan mot nordväst. / <p>Examensarbete F1 på 7 p (10,5 hp)</p>

Two days in May 1997 has been studied. During one of the days a sea breeze circulation occured, and the two days were compared in search for effects from the sea breeze on the fluxes in the marine boundary layer. Measurements were made on a tower at the small island Östergarnsholm east of the island Gotland, and by an instrumented aircraft over the sea east and west of Gotland. The direction of the geostrophic wind were about northwest during the time period, but 17 m/s during May 3 and 7 m/s during May 4. The stratification was stable over the main part of the Baltic sea because of the large temperature differences between land and sea surfaces. But as the sea breeze developed and the wind direction turned to the southeast, the stratification at Östergarnsholm changed to near neutral. Both the wind speed and the fluxes decreased with distance from the Swedish mainland and the west coast of Gotland, and the fluxes were over all very small. The momentum flux showed no big difference between the days. Because of the decrease with the distance from the coast and the wind speed it was concluded that the stratification was of greater importance than the sea breeze circulation for the momentum fluxe. But the heat flux was affected by the sea breeze. Because of the sea breeze the stratification became neutral, and thus the heat flux very small. The presence of swell in the baltic sea was also studied. The correlation coefficient gave unexpected result during May 3, with no difference for swell and no swell conditions. The angle between the swell and the wind wave was about 90° during both days, and could not be the reason for the difference. During the May 3 the stratification was mostly stable, while it on May 4 was unstable. It is suggested that this could be a reason for the behaviour of ruw.

The wind climate in a valley has been studied. Long time data from towers along the valley have been used, together with data from two field campaigns. The campaigns took place during two weeks in May 1999 and two weeks in September 2000. During the field campaigns wind speed and direction were measured, both with small masts and with pilot balloon tracking. A comparison of single and double theodolite tracking is performed. It is found that single theodolite tracking is good enough to use. The ascent rate of the balloon is seen to be slightly higher than the earlier assumed 4 m/s. An investigation of the wind field along and across the valley have been done. The result show that high mean wind speed are found at the sites were the valley is rather narrow. The wind direction was then either upstream or downstream the valley. The mean wind speed at Suorva is 6.6 m/s. Channelling effects, forced- and pressure-driven channelling, seem to dominate the winds in the valley giving high speeds. No correlation is found between the magnitude of the geostrophic wind and the wind in the valley. High winds in the valley is obtained both with high and low geostrophic winds. A peak in the southwesterly direction for the distribution of geostrophic wind is seen. This is due to the common synoptic situation with a low pressure area outside the coast of Norway. Data from sites across the valley show that the highest wind speeds are found at the northeastern side and the lowest at the southwestern side. The stratification is found to have strong effect of the air flow around a hill and the local terrain. When the stratification was stable the air was blowing around Jiertasuoloj, an island of about 50 m height. When the air is unstable the air is instead blowing over Jiertasuoloj.

In order to study the impact of climate change on the Earth's hydrologic cycle, global information about snowfall is needed. To achieve global measurements of snowfall over both land and ocean, satellites are necessary. While satellites provide the best option for making measurements on a global scale, the task of estimating snowfall rate from these measurements is a complex problem. Satellite-based radar, for example, measures effective radar reflectivity, Ze, which can be converted to snowfall rate, S, via a Ze-S relation. Choosing the appropriate Ze-S relation to apply is a complicated problem, however, because quantities such as particle shape, size distribution, and terminal velocity are often unknown, and these quantities directly affect the Ze-S relation. Additionally, it is important to correctly classify the phase of precipitation. A misclassification can result in order-of-magnitude errors in the estimated precipitation rate. Using global ground-based observations over multiple years, the influence of different geophysical parameters on precipitation phase is investigated, with the goal of obtaining an improved method for determining precipitation phase. The parameters studied are near-surface air temperature, atmospheric moisture, low-level vertical temperature lapse rate, surface skin temperature, surface pressure, and land cover type. To combine the effects of temperature and moisture, wet-bulb temperature, instead of air temperature, is used as a key parameter for separating solid and liquid precipitation. Results show that in addition to wet-bulb temperature, vertical temperature lapse rate also affects the precipitation phase. For example, at a near-surface wet-bulb temperature of 0°C, a lapse rate of 6°C km-1 results in an 86 percent conditional probability of solid precipitation, while a lapse rate of -2°C km-1 results in a 45 percent probability. For near-surface wet-bulb temperatures less than 0°C, skin temperature affects precipitation phase, although the effect appears to be minor. Results also show that surface pressure appears to influence precipitation phase in some cases, however, this dependence is not clear on a global scale. Land cover type does not appear to affect precipitation phase. Based on these findings, a parameterization scheme has been developed that accepts available meteorological data as input, and returns the conditional probability of solid precipitation. Ze-S relations for various particle shapes, size distributions, and terminal velocities have been developed as part of this research. These Ze-S relations have been applied to radar reflectivity data from the CloudSat Cloud Profiling Radar to calculate the annual mean snowfall rate. The calculated snowfall rates are then compared to surface observations of snowfall. An effort to determine which particle shape best represents the type of snow falling in various locations across the United States has been made. An optimized Ze-S relation has been developed, which combines multiple Ze-S relations in order to minimize error when compared to the surface snowfall observations. Additionally, the resulting surface snowfall rate is compared with the CloudSat standard product for snowfall rate. / A Dissertation submitted to the Department of Earth, Ocean and Atmospheric Science in partial fulfillment of the Doctor of Philosophy. / Spring Semester 2017. / March 31, 2017. / Atmospheric Science, Hydrology, Meteorology, Remote Sensing, Snowfall / Includes bibliographical references. / Guosheng Liu, Professor Directing Dissertation; Anke Meyer-Baese, University Representative; Mark A. Bourassa, Committee Member; Ming Cai, Committee Member; Philip G. Sura, Committee Member.

The cold blob refers to an observationally unprecedented, gyre-scale, record-breaking cold of mean surface temperature over the subpolar North Atlantic. Its anomalous cold feature goes against the rising trend of global mean surface temperature in the context of a warming climate. Observations show that the Atlantic cold blob emerged in early 2014 and can penetrate deeper into the ocean interior beyond 500m depths. A sudden drop in upper ocean heat content is associated with an accumulative increase in freshwater content. Prior works pointed out that intense surface forcing during two consecutive winters was a primary driver. We hypothesize that surface forcing alone is insufficient for the cold blob to persist. Our analysis shows, for the first time, that variations in the net surface heat fluxes cannot explain the decline in upper ocean heat content during 2014–2017. Therefore, surface forcing fails to explain the origin of the cold blob. To investigate alternative mechanisms, non-assimilative simulations based on a coupled ocean-sea ice model (GFDL MOM5/SIS1) with two different atmospheric forcings (MERRA2 and ERA-interim) are employed to examine the transports of mass, heat, and freshwater within the cold blob area. Initial diagnosis verified that both model runs can reproduce the cold blob characteristics at similar magnitudes to Argo observations. Model results show a decreasing trend of heat transport at the southern boundary, implying that reduced poleward ocean heat transport likely accounts for the formation and persistence of the cold blob. This cooling signal from the south is accompanied by a freshening signal. Changes in the residual heat fluxes suggest that reduced warming for the subsurface layer at 100–700 m depths apparently occurred since 2006 before turning into enhanced cooling during late 2013. Variations in the residual freshwater fluxes remain positive for the entire past decade and subsequently result in an accumulative surplus of freshwater content in this area. The model run with incorporated Greenland meltwater estimates sheds light on the relative contribution of meltwater advection. To a great extent, Greenland meltwater can amplify the freshening tendency in the subpolar North Atlantic by approximately up to 200% during the present decade. In the long run, upper ocean cooling and freshening would lead to increased stratification and reduced mixing with deeper waters, therefore enhancing the likelihood that the subsurface cold blob persists. / A Dissertation submitted to the Department of Earth, Ocean and Atmospheric Science in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Fall Semester 2018. / November 5, 2018. / Air-Sea Interaction, Climate Change, Cold Blob, Greenland Meltwater, Polar-Lower Latitude Linkage, Subpolar North Atlantic / Includes bibliographical references. / Mark A. Bourassa, Professor Directing Dissertation; James B. Elsner, University Representative; Allan J. Clarke, Committee Member; William K. Dewar, Committee Member; Kevin G. Speer, Committee Member.

<p> Generic predictions for the acoustic wavenumber at low frequencies in the condensational cloud layers of Venus are presented, based on and adapted from the terrestrial model of Baudoin <i>et al.</i> (J. Acoust. Soc. Am. <b>130.</b> 1142 (2011)). While the general thermodynamics of Earth clouds is well understood, that of Venusian clouds is still a matter of debate. Venus&rsquo; clouds are primarily formed of H₂O and H₂SO₄ vapors and aqueous sulfuric acid droplets, the fluxes of which are not fully constrained due to the few in situ observations. Inside the clouds, the Navier-Stokes-Fourier equations of continuum fluid mechanics are used for the gaseous (dry + vapor) and liquid phases of H₂O andH₂SO₄, combined with equations describing the evaporation/condensation processes; the gaseous phase is treated as an ideal gas and the liquid droplets are considered polydisperse. Thermophysical parameters are interpolated at the ambient conditions pertaining to an altitude of 50 km, a level where balloon platforms (e.g., European Space Agency&rsquo;s EVE) and manned airships (e.g., NASA&rsquo;s HAVOC) may be deployed in the future. At low frequencies, the dominant source of absorption is caused by the evaporation/condensation of the liquid phase. At higher frequencies, absorption is dominated by momentum transfers between the wave and the ambient gas and liquid droplets. The intrinsic dispersion is negligible. Sensitivity studies of the attenuation coefficient and the sound speed on the cloud physical parameters is performed, namely, the mean cloud particle size and the cloud density. The attenuation coefficient is sensitive to changes in both mean cloud particle size and cloud density, while the intrinsic dispersion changes negligibly. </p><p>

A numerical model of the global carbon cycle is presented which includes the effects of anthropogenic &CO\sb2& emissions &(CO\sb2& produced from fossil fuel combustion, biomass burning, and deforestation) on the global carbon cycle. The model is validated against measured atmospheric &CO\sb2& concentrations. Future levels of atmospheric &CO\sb2& are then predicted for the following scenarios: (1) Business as Usual (BaU) for the period 1990-2000; (2) Same as (1), but with no biomass burning; (3) Same as (1), but with no fossil fuel combustion; (4) Same as (1), but with a doubled atmospheric &CO\sb2& concentration and a 2 K warmer surface temperature associated with the doubled atmospheric &CO\sb2& concentration. The global model presented here consists of four different modules which are fully coupled with respect to &CO\sb2.& These modules represent carbon cycling by the terrestrial biosphere and the ocean, anthropogenic &CO\sb2& emissions, and atmospheric transport of &CO\sb2.&. The prognostic variable of interest is the atmospheric &CO\sb2& concentration field. The &CO\sb2& concentration field depends on both the sources and sinks of &CO\sb2& as well as the atmospheric circulation. In addition, the sources and sinks vary significantly as a function of both time and geographic location. The model output agrees well with measured data at the equatorial and mid latitudes, but this agreement weakens at higher latitudes. This is due to the less adequate representation of the terrestrial ecosystem models at these latitudes. In the first scenario, the predicted concentration of atmospheric &CO\sb2& is 362 parts per million by volume (ppmv) at the end of the 10 year model run. This establishes a baseline for the next three scenarios, which predict that biomass burning will contribute 3 ppmv of &CO\sb2& to the atmosphere by the year 2000, while fossil fuel combustion will contribute 5 ppmv. The net effect of a 2 K average global warming was to increase the atmospheric &CO\sb2& concentration by approximately 1 ppmv, due to enhanced respiration by the terrestrial biosphere.

The role of the continent of Africa as a source of gaseous and particulate emissions to the atmosphere is investigated in this study. Sources of gases and particulates from Africa include fossil fuel combustion, biomass burning, and biogenic soil emissions of nitric oxide. This study represents the first comprehensive database of gaseous and particulate emissions developed for the continent of Africa on a country by country basis and establishes the framework for country-by-country, assessment of greenhouse gases emissions as required by the Kyoto Conference on Global Warming, which was attended by representatives from more than 100 countries. Calculations of gases and particulates resulting from fossil fuel combustion were based on the Intergovernmental Panel on Climate Change (IPCC) guidelines. Calculations of gases and particulates resulting from biomass burning were based on fire counts obtained from the Defense Meteorological Satellite Program (DMSP). Block 5 satellites and emission ratios for various gaseous and particulate fire products obtained during the recent Southern African Fire-Atmosphere Research Initiative (SAFARI), an activity of the international Global Atmospheric Chemistry (IGAC) Project, part of the international Geosphere-Biosphere Program (IGBP). The calculations of biogenic soil emissions of nitric oxide were obtained with the NOAA Geophysical Fluid Dynamics Laboratory (GFDL) Biogenic Soil NO&\rm\sb{lcub}x{rcub}& Model. Africa was found to be a significant global source of the following gases: carbon dioxide (CO&\sb{lcub}2{rcub}&), carbon monoxide (CO), methyl chloride (CH&\sb{lcub}3{rcub}&Cl), oxides of nitrogen &\rm(NO\sb{lcub}x{rcub}),& and carbon particulates. The results indicate that Africa is the world's single largest continental source of emissions due to biomass burning and that these emissions are likely to increase with time. The study established that on a global scale, Africa was the largest source of soil biogenic NO&\rm\sb{lcub}x{rcub}&. The importance of Africa as a key global source of trace gases and aerosols has been underestimated in the past. This research offers a new picture of gaseous and particulate emissions from Africa. Africa's global significance as a source of atmospheric gases is very important, i.e., more than 11% of the world's total anthropogenic CO&\sb{lcub}2{rcub}& production results from biomass burning in Africa. Africa contributes nearly a third of the global anthropogenic CH&\sb3&Cl, a third of the global anthropogenic &\rm NO\sb{lcub}x{rcub},& and almost 20% to the world's global carbon particles anthropogenic budget.