EVALUATING ERA5 WEATHER PARAMETERS DATA USING REMOTE SENSING AND IN SITU DATA OVER NORTH RED SEA

: High demand is placed on atmospheric studies specially for climatic characteristics, in order to cooperate with the government vision for exploitation of marine resources and a great potential for renewable energy, including solar, wind, hydro and geothermal energy as well as the huge expansion in coastal construction projects planned in the Egyptian Red Sea coasts for establish and growth of industry, tourism and urbanization. This study analyse the recent trends of Surface Wind (W10), surface air temperature (T2m), relative humidity (RH2m) and surface pressure (MSLP) using the European Centre for Medium-Range Weather Forecasts (ECMWF) latest fifth-generation reanalysis weather elements product global Reanalysis dataset (ERA5) Compared to Satellite Earth Observation (EO) altimetry remote sensing data (MERRA-2) and local observed data from chosen WMO automatic weather stations (AWS) over North Red Sea coasts in Egypt, Hourly data records were acquired from four WMO weather stations, deployed in different locations: Suez, Sharm Elshaikh, Safaga, Marsa Alam to study regional Climatic Characteristics, test and validate ERA5 data and evaluates the ability of ERA5 reanalysis to reproduce hourly and monthly averages for weather characteristics over North Red Sea, with hourly time series for data spans approximately 11 years, period from January 2012 to December 2022. Results of the analysis expected to reveal the agreement between remote sensing data, observations and ERA5 estimates, determine correlation values and Root Mean Square Error (RMSE). Based on certain considerations outlined in this paper, it is appropriate to use MERRA-2 and ERA5 to characterize T2m, RH, W10 and MSLP over North Red Sea.


INTRODUCTION 1.1 Overview
Due to the lack of climatic studies and knowledge over the North East Red Sea area and the importance of the climatic characteristics for all human activities and due to the unique topography and hydrography of the Red Sea coasts over Egypt and due to the high impact of climate change all-over the globe its crucial to give more attention for climatic studies specially over such a promising areas.
Global studies for climate change mentioned that increase in temperature has impacts such as: increased incidence and severity of heat-waves, droughts.Over Egypt, there has been a number of mega heat waves in the last decade, particularly the record-breaking summers of 2010, 2012, 2015 and 2018, which caused the loss of life and severe economic damage to many sectors (e.g.agriculture, energy, water resources) (M.Eid, 2019)

Area of Study
Red Sea is a Longitudinal narrow semi-enclosed tropical body of water connected at the north with the Mediterranean through the Gulf of Suez and the Suez Channel and to the south with the Indian Ocean by strait of (Bab El Mandab), separating northeast Africa from Sinai Peninsula Lies between latitudes 30°N and 12° 30´N, Longitudes 33° and 44°E, with dimensions 1045 Nautical Mile long, 151 Nautical Mile average width , the total surface area of the Red Sea estimated between 438 and450 Km2, while the volume is between 215 and 251 Km3, The average depth is considered to be 491 m, The maximum depth recorded in the Red Sea is 2850 m which is small compared with oceans but it's large compared with such a body of water with its size (Gladstone, 2006) and is bordered by Egypt, Sudan, Eritrea and Djibouti on the west, and Yemen and Saudi Arabia on the east.Although the Red Sea is known for its natural beauty, with extensive corals reefs, South of Lat.24° a deep incision, referred to as the axial trough, appears in the main basin.
This can be followed along the length of the Red Sea as far as 16°N.North of Lat.22°N the coastal plains tend to be narrower (Nautical charts 158; 159, 2023) 500m contour is set back around 40 km from the coast, giving a wider coastal plain.From Egypt to the Sudanese border the coastline has large areas of sandy beaches, with far fewer areas of rocky coastline.Relatively straight coasts, few bays and inlets, no rivers discharge to continually taking materials into the Red Sea, have great effect on the continental dry climate in Africa.Wadis at various points along this coast carry runoff to the sea when occasional local rains fall.Most wadis are small.Further inland at a distance of 60 km from the coast occasional hills rise to 1,500 m or more (Gladstone, 2006).it is also an important shipping route for maritime transportation through the Suez Canal.
This study focused on Egyptian coasts over Northern Red Sea, coordinates latitudes (from 30° 30' N to 22° 00' N) and longitudes (from 32° 00' E to 39° 30' E) based on data from four (WMO) automatic weather stations (AWS) as shown in figure (1).

Data Collection
Data was collected from three main sources: .Bathymetric chart of the study area with the four considered weather observation stations: 1) Suez, 2)Sharm Elshaikh, 3) Safaga, 4) Marsa Alam.Regional winds are showed.

Climatic Conditions
Semiarid climate According to the Koppen classification system, a system of climate classification using latitude band and degree of continentally as its primary forcing factors, a predominantly (BWh) type climate regime (the main climate is arid, the precipitation type is the desert type, and the temperature is high).This implies that the annual precipitation is less than 50% of this threshold, which factors in seasonal distribution of rainfall and the degree of dryness/coldness of the season and signified lowlatitude climate (average annual temperature above 18°C) (Oliver, 2005).
Climatically, generally warm temperatures, dry summers, winter -dominated rainfall, and a profusion of microclimate due to local terrain, characterize the Red Sea.

Air temperature (T2m)
Average temperature increased in the eastern coast of Egypt because of the warm waves from the Arabian Peninsula and Eastern Mediterranean caused by warm Indian Monsoon lowpressure centre.In North Red Sea the air temperature exceeds the sea surface temperature by greatest value in the summer months, which is fairly influenced by conditions of an adjacent land.In winter air temperature is less than the sea surface by about half a degree.The mean diurnal range of air temperature is 4°C, from December to April, and 6°C in July, where 5°C in all other months, Generally maximum temperature occurs two hours after noon and minimum at sunrise, some changes happens because amount of heat lost by Earth at day or night (Hamed, 2002).
More incoming solar radiation (insolation) occurs with smaller incident angle when moving to the equator, the longer day time in summer months gives more radiation, over the area of study, maximum insolation happens in July and minimum in January.
Rocks and sand land have very high albedo, which increase the daily temperature variation.
Due to rapid laps rate, altitude of the observed area is one of the most important factors in determining Air temperature, high slope of the mountains to the sea side has huge effect of the temperature over the mountains areas which is adjacent to the coast, while the narrow coastal plain makes the declination is neglected at the Red Sea coast.The main body of the Red Sea, between latitude 16°N and 26°N, more than 75% of winds in all months of the year are of force 4 or less (0-16knots), and in the summer and autumn months this figure rises generally to over 80% and may exceed 85%.The mean annual wind speed is less than 10 knots and gales are rare.
In most months the wind is observed as "calm" (less than 1 knots), on more than 5% of occasions, In the North Red Sea area, winds of force 5-6 (17-27knots) account for about 10% of observation in the summer and about 20% in mid-winter.The region of North Red Sea, including the Gulf of Suez, tends to have strongest wind throughout the year than the area just described.In the months, winds of force 4 or less occur between 60% and 70% of the time.The mean annual speed is a little over 10 knots and September is the windiest, and all winds appear to be rather higher on the Egyptian side.Winds of force 5-6 usually account for some 20-25% of observation.This figure is varying from about 15% in mid-winter to about 35% in September.
Occasional gales occur throughout the year with isolated instance of force 11 to 12 being on record.

Methods of analysis
To evaluate the quality of the ERA5 reanalysis data set for the North Red Sea area, ERA5, remote sensing and in situ data were collected.For data preparation the dataset was categorized and inspected for spikes, outliers, and incorrect data readings before smoothing.
As a quantitative research, descriptive statistical analysis method were used for data preparation, processing, analyzing and visualization using the following computer software: (Matlab, Excel, CSVploter, Windrose.xyz,ERA5 explorer and Agrometeorological indicator explorer and data extractor) correlation coefficient (r) used as one of the metric criteria for the remote sensing, observed and reanalysis dataset, and root-meansquare-error (RMSE) were used to focus on errors, the relative bias (BIAS) are synthesis indices described by the correlation component and bias which were computed to investigate the relationship between the ERA5 reanalysis, remote sensing data and observed data at the 4 meteorological stations at hourly temporal scale.
Figure 2. monthly averages temperature at North Red Sea in ºc Source: Egyptian Naval Hydrographic Department, 20222.3Wind Regime (W10)Along the Red Sea coast, winds blow predominantly (65-70%) from the directions (N, NW and W).Winds from North Easterly directions occur during (10 -15%) of time and the rest from the other direction.Speed average 5 -15 knots most of the year with higher velocities from North Westerly directions.Extreme winds occur in storms of which about 15 knots passes during a winter.The most effective wind direction to ships at port is South-Easterly wind because it brings swell, especially with high wind speeds.
Monthly averages for (W10) over the North Red Sea are represented in wind roses in figures (3) and (4).

Figure 6 .
Figure 6.Monthly average relative humidity over North Red Sea Source: Egyptian Naval Hydrographic Department, 2023.As shown in fig.(7) the diurnal humidity variation determined by absolute humidity and air temperature, in morning the rate of temperature increase more than the increase of the absolute humidity and vice versa during night time.Relative humidity inversely proportional with air temperature and the maximum happens at sunrise and the minimum value two hours after noon.The temperature, absolute humidity and the relative humidity diurnal varies with passing of more humid air mass during wind direction changes.

Figure 7 .
Figure 7. Relation between temperature and absolute humidity needed for air to be saturated, Source: USAF, 2022.
ERA5 monthly averaged Eastward (U), Northward (V) component of wind at a height of 10m and hourly temperature of air at 2m above the surface (T2m) Over the study area for the given time series shown on Figures (8,9) respectively using historical climate statistics interface (ERA5 explorer) available online:(https://cds.climate.copernicus.eu/cdsapp#!/software/app-era5-explorer?tab=app).Relative humidity at a height of 2metres above the surface (the amount of water vapour present in air expressed as a percentage of the amount needed for saturation at the same temperature) shown on figure (10) using Agrometeorological indicator explorer and data extractor online: (https://cds.climate.copernicus.eu/cdsapp#!/software/appagriculture-agera5-explorer-data-extractor?tab=app).

Table 2 .
Positions and elevations of meteorological stations Source: Egyptian Meteorology Authority (EMA), 2023

Table 3 .
Comparison analysis between observed and ERA5 weather variables over Suez, Sharm elShaikh, Safaga and Marsa Alam: n = number of observations, R = correlation coefficient.As seen in (Table 3), By comparing both results of the weather parameters over the study area, the highest (T2m) occurs over Sharm Elsheikh with avg.mean (26.74 c°) and the minimum annual mean (23.51) over Suez.The most humid station is Suez with avg.RH (55.89%) and the minimum humid mean (40.53%) over Sharm Elsheikh.(WS10) measured in (m/sec) showing that the highest wind speed over Safaga mean (5.16 m/sec) and the minimum mean over Suez (3.51 m/sec).Avg.(MSLP) over Suez (1013.6 hpa) and over Sharm Elsheikh (1010.71hpa).RMSE values represent the absolute error between the ERA5, MERRA-2 and observed values as shown in (table 4). the calculation formula is described as follows.!−  ! ) "  Where 0 are the observed values; E are ERA5 values; ∑ represents 'sum'; and  is the number of observations.