In this thesis new methods have been developed for the recovery of past surface temperaturevariations from underground temperature-depth profiles. This has been undertakenfrom a Bayesian standpoint with an emphasis on model comparison, which allowsdifferently parameterised inverse models (inferred past temperature histories) to be automaticallyconstructed and compared in the light of the data and the prescribed priorinformation. In the first contribution a new method for inverting temperature-depth profiles ispresented which relies on trans-dimensional Bayesian sampling. The temperature historiesare parameterised in terms of a variable number of linear segments over time. Relying onthe natural parsimony of Bayesian inference, whereby simpler models which can adequatelyexplain the data are preferred, the complexity or roughness of the temperature historiescan be determined without the need for explicit a priori smoothing. This method thereforeallows a more objective inference of the past temperature changes. These concepts are extended to the spatial domain in the following chapter using themethod of Bayesian partition modelling. This seeks to find the posterior distribution ofthe number and spatial distribution of independent temperature histories given a spatiallydistributed ensemble of temperature-depth profiles. The results from applicationto 23 real boreholes in the UK are discussed in detail and show a clear preference for8 or 9 independent (and mostly contrasting) temperature histories. It is thus concludedthat the majority of these data cannot be considered as reliable sources of palaeoclimatereconstruction. A 3D finite element heat transfer forward model is developed in the latter part of thethesis, and is used to simulate underground temperatures. This forward model is linked to the first of the two Bayesian inverse methods described above. The effect of the reductionin average ground surface temperature with altitude is included in the forward model andinversion of the resultant profiles using a 1D forward model is shown to give significantdiscrepancies in the inferred temperature histories. Finally the inversion results fromthe Bayesian formulation are compared with those using a conventional gradient descentmethod. The thesis concludes with some possibilities for future research in this field which buildsupon the work presented herein.

We investigate solar cycle signals in 150 years of Sea Level Pressure (SLP) and Sea Surface Temperature (SST) data, using multiple regression analysis. We detect a solar signal in both SLP and SST in the North Pacific during DJF, similar to that found by Van Loon et al. (2007) but of smaller magnitude. We do not, however, identify the signal they found in the tropics. Our results do not support mechanisms for a solar influence on climate directly involving tropical SSTs. We have used different reconstructions of total solar irradiance to investigate the sensitivity of the results. The series of Krivova & Solanki and Foster give similar results to those acquired using sunspot number but the Hoyt & Schatten solar index sometimes produces different results because of mixing of the solar signal with a long-term trend. Using different approaches Labitzke and van Loon (1992) and Camp and Tung (2007), arrived at different results for a solar influence on winter stratospheric polar temperatures and its relationship to the quasi-biennial oscillation (QBO) in tropical stratospheric zonal winds. We show that these differences appear different largely because of their choices of QBO height. We also show that the effect of the QBO (30, 40 or 50 hPa) combined with solar activity reveals a clear signal in polar annular modes expressed in SLP. We show that the nature of ENSO was different before 1950s (and after1997): this may affect any solar influence. Other authors have suggested that tropical circulations were different during the intervening period. Such observation may have implications relating to the sun, tropical circulation and climate change. During 1958-1997, omission of ENSO from regression gives false warming (cooling) signal of higher (lower) solar on SST in tropics. Such analysis, accompanied by our observation that the years of peak annual sunspot number used by van Loon et al. (2007) generally falls a year or more in advance of the maximum of the smoothed DSO, provides coherence to some apparently conflicting findings. Finally, an atmosphere-ocean coupling process, (mainly involving the Pacific Ocean) is proposed to account for the solar influences. This coupling appears to be disturbed during the later half of the 20th century, probably due to climate change.

The work described in this thesis concerns the effect of cirrus clouds on far-infrared (FIR) radiance spectra. Though the importance of both FIR radiation and cirrus clouds to the Earth’s energy budget is well recognised, few high spectral resolution measurements have been made at FIR wavelengths to date. Observations taken during two diverse field campaigns, along with spectra simulated using a radiative transfer model, are used here to investi- gate the FIR signature of cirrus. The FIR observations presented are made using the TAFTS spectrometer, which measures spectral radiances from ei- ther an aircraft or the ground. The deployment of TAFTS during the RHUBC campaign based in Barrow, Alaska is described. TAFTS was used to make ground-based FIR observations of the arctic atmosphere, both with and without cirrus. Comparing these with modelled spectra, which assume a parameterised particle size distribution (PSD) when describing the cirrus microphysics, suggested that the PSD parameterisation underestimates the fraction of ice water content contributed by small ice crystals. This conclusion is corroborated by AERI-ER observations made simultaneously at the Barrow site during RHUBC. TAFTS observations of convective tropical cirrus made during EMERALD- II near Darwin, Australia are also presented here. During EMERALD-II TAFTS was deployed on an aircraft, enabling spectral measurements of cirrus at wavenumbers between 100 and 200cm−1 to be made for the first time. Comparisons with LBLDIS spectra calculated using PSDs measured using cloud probes indicate that the number of small crystals measured may be too high by a factor of three. This result is in agreement with previous studies suggesting that small crystal populations are over-counted by in-situ cloud probes, due to shattering of larger crystals on the probe inlets. The results from both campaigns illustrate the sensitivity of FIR radiances to cirrus properties, with particular emphasis on the effect of small ice crystals.

Understanding the land–boundary layer–sea interactions is a primary target both in the context of low-level jet (LLJ) development and landscape alterations. This thesis attempts to address and study these interactions in the Middle East. The thesis investigates the summertime LLJ over the Persian Gulf, known as the Shamal. Terrain height, land-sea and novel mountain slope sensitivity experiments were conducted and compared with a control run. It was found that the Weather Research and Forecasting (WRF) model accurately simulates the LLJ’s vertical structure, nocturnal features and strong diurnal oscillation of the wind, and that orography, mountain slope and land/sea breezes determine the Shamal diurnal variation of wind speed and wind direction. The Iranian mountain range not only channels the northwesterly winds but also provides a barrier for the easterly monsoon airflow. The steep slopes cause increased wind speeds; however, the shallow slopes reveal a stronger diurnally varying wind direction due to larger diurnal heating of the sloping terrain. The land breeze and the lower friction over the sea increase the intensity of the nocturnal jet over the Gulf. To determine the effects of the Nile Delta man-induced greening on local climate, the WRF model was used to compare control simulations, which employ the present-day Nile Delta landscape, with desertification experiments in which the Nile Delta is replaced by desert. It was found that the low surface albedo of the present-day agricultural Nile Delta increases net radiation, which in turn raises potential evapotranspiration (PET). This suggests that agricultural use increases the water demand by enhancing PET. Non-local effects were also examined. It was found that a frontal system over the eastern Mediterranean Sea, associated with a storm event, is shifted farther away from the coast. This shift is attributed to a stronger land breeze in the present-day land-cover.

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KEYWORDS: Svalbard, glacial, fjord, Holocene, climate General circulation models predict that climatic warming will initially be manifest in a decrease in ice volume at high latitudes and a corresponding rise in global sea level. This study has been prompted by two factors: (i) the recognition of rapid climate change and the concern of the magnitude of its progress; (ii) instrumental records of climatic variation exceed a century, rarely two centuries, yet are temporally too short and spatially incomplete to reveal the full range of seasonal to millennial-scale variability. A transect of sediment cores were collected from the basins of glaciated Kongsfjorden on the northwestern coast of Svalbard. The cores were investigated for lithology, grain size, ice rafted debris, organic carbon, foraminifera, and stable isotopes in foraminiferal tests. Age control was provided by seven AMS radiocarbon ages combined with core top 210Pb chronology. The recovered sedimentary sections span a range of ages, reaching a maximum of ca.6000 years. The proxy records reveal variations in sedimentary processes, bioproductivity, glacier front position, sea ice conditions, and the hydrographic regime in the fjord. These characteristics are interpreted in terms of regional and global climate changes during the mid and late Holocene. The records reveal warm stable conditions for three millennia subsequent to 6000 yrs BP. Initial Neoglacial cooling occurred between 3000 and 2000 yrs BP followed by intervals of ameloriated marine conditions between 1300 and 900 and between 500 and 280 yrs BP, briefly interrupting the decreasing trend in productivity that culminated in the Little Ice Age.

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The north-south gradient in surface temperature and rainfall in West Africa leads to the summertime monsoon circulation. Here, the full extent of the relationship between the land surface and the atmosphere is discussed with particular reference to the impact that soil moisture has on the atmosphere at different spatial scales. Observations from the AMMA field campaign in 2005 and 2006 are combined with satellite analysis and model simulations to discuss various interactions between the land surface and the atmosphere. Tethered balloon observations from Mali in August 2005 are used to assess the characteristics of the nocturnal boundary layer. It is observed that a stronger surface temperature inversion after sunset leads to a faster nocturnal jet, and these findings are further investigated using surface station data. Case studies of two nights of observations are used to discuss the variation of observed boundary layer structures. It is found that on nights where the nocturnal jet is weaker, the winds align with African Easterly Wave (AEW) circulations on the larger scale. . Following this, the impact that AEWs had on sl1rface properties is examined. Flux data from Niamey showed little statistical correlation with wave passage. It is suggested this could be partly due to the study year having more westerly initiating waves than climatology. The inducement of circulations by soil moisture inhomogeneities are discussed in regard to previous literature, where a moist cool surface leads to high pressure and anticyclonic circulation. The relation of this theory to the synoptic scale is investigated using a case study from 25-29 July 2006. During this time, an unusually-structured AEW left a distinct synoptic 'wave' pattern of soil moisture in the Sahel region due to its modulation of convection. The structure of this wave and the initial conditions which lead to the soil moisture pattern are discussed. The atmospheric impact of the soil moisture wave is investigated using the Met Office Unified Model. It is found that th~ enhanced soil moisture leads to a cooler, moister, . thinner boundary layer. This leads to divergent winds at low levels and a reduction in the monsoon flow due to the reduction in the north-south pressure gradient. There is indication that low-level anticyclonic circulations are enhanced. The enhanced soil moisture wave also leads to an increase in easterly winds at the African Easterly Jet level: it is shown that this is due to a decrease in boundary layer height and a reduction in turbulence. Inspection of wave energetics shows the case study wave appears to be in a decaying phase. There is evidence that the soil moisture wave increases the thermal decay by decreasing the temperature behind the trough in the warm region, reducing the temperature eddies and re-establishing the zonal temperature gradient. This study has implications for weather forecasting as the results suggest that patterns in soil moisture on the large scale are able to alter atmospheric dynamics at the synoptic scale within the time frame of a few days. This leads to further questions as to whether a realistic representation of soil moisture in mo.dels would lead to an improvement in the simulation 'of tropical synoptic dynamics.