🌡 Instruments

Instruments used in meterology, weather modification, important terms and isopleths.

Weather Modification

👉🏻 Weather modification refers to willful manipulation of the climate or local weather.

Exploding demand of water resources and continued population growth has given rise to the problem of water scarcity in many regions of our planet.
To meet the demand of water resources scientist have started using weather modification commonly called as cloud seeding.
Cloud seeding is a weather modification technique which involves the introduction of material into a cloud (using aircraft or ground-based generators) with a view to encouraging the formation and growth of ice crystals or raindrops and, in turn, enhancing the precipitation (snow and/or rain) falling from the cloud.

👉🏻 There are two basic types of cloud seeding - Cold and Warm:

Cold cloud seeding (glaciogenic seeding) involves adding particles such as silver iodide crystals or dry ice pellets to the super-cooled (below freezing point) water already present in clouds to promote the formation of ice crystals. The ice crystals grow, fall and melt to below the freezing level to become raindrops.
Warm cloud seeding (hygroscopic seeding) involves adding salt particles (sodium chlorides, magnesium chlorides and calcium chlorides), which attract water into or just below the base of suitable clouds to enhance the growth of cloud droplets by coalescence.

Growing degree days (GDD) is a weather-based indicator for assessing crop development.
It is a calculation used by crop producers that is a measure of heat accumulation used to predict plant and pest development rates such as the date that a crop reaches maturity.
In the absence of extreme conditions such as drought or disease, plants grow in a cumulative stepwise manner which is strongly influenced by the ambient temperature.
The Growing Degree Days calculation allows producers to predict the plants’ pace toward maturity.
Daily growing degree day values are added together from the beginning of the season, providing an indication of the energy available for plant growth.
Growing degree day totals are used for comparing the progress of a growing season to the long-term average and are useful for estimating crop development stages and maturity dates.
Growing Degrees (GDs) is defined as the mean daily temperature (average of daily maximum and minimum temperatures) above a certain threshold base temperature accumulated on a daily basis over a period of time.
Negative values are treated as zeros and ignored.
The base temperature varies among crops and the value is derived from the growth habits of each specific crop.
The base temperature is that temperature below which plant growth is zero. For example, cereal and forage crops show little growth or development when average temperatures are below 5°C.

GDD Calculation

GDs are calculated each day as maximum temperature plus the minimum temperature divided by 2 (or the mean temperature), minus the base temperature.
GDDs are accumulated by adding each day’s GDs contribution as the season progresses.
If the average temperature is below the base temperature, the growing degree day value for that day is zero.
GDD = (T_max + T_min)/2 - T_base

The temperature at which the plant cell gets killed when the temperature ranges from 50-60°C.
This varies with plant species.
The aquatic and shade loving plants are killed at comparatively lower temperature (40°C).

Injury caused on the barks of stem by high temperature during daytime and low temperature during the night time.

The stem at ground level scorches around due to high soil temperature.
It causes death of plant by destroying conductive tissue.
Eg. This type of injury is very common in young seedlings of cotton in sandy soil when soil temperature exceeds 60°C.

Low pressure centre surrounded by winds having their velocities in the range of 40 to 120 km/hour.

A severe tropical cyclone with wind speed exceeding 120 km per hour.
The name hurricane is given to the tropical cyclones in the North Atlantic and the eastern North Pacific Ocean.

Defined as a violently rotating column of air attended by a funnel-shaped or tubular cloud extending downward from the base of cumulonimbus cloud.

Plants which are adapted to hot climate, if exposed to low temperature for sometime, are found to be killed or severely injured or development of chloratic condition (yellowing) (eg.) cholratic bands on the leaves of sugarcane, sorghum and maize in winter months when the night temperature is below 20°C.

A type of cold injury which is commonly observed in plants of temperate regions. When the plants are exposed to very low temperature, water freezes into ice crystals in the intercellular spaces of plants.
The protoplasm of cell is dehydrated resulting in the death of cells. • (E.g.) Frost damage in potato, tea etc.

In temperature regions, usually during the winter season, the ice or snow forms a thick cover on the soil surface.
As a result, the entry of oxygen is prevented and crop suffers for want of oxygen.

This is a kind of injury caused by lifting up of the plants along with soil from its normal position.
This type of injury is commonly seen in temperate regions.
The presence of ice crystals increases the volume of soil.
This causes mechanical lifting of the soil.

The oasis effect refers to the creation of a local microclimate that is cooler than the surrounding dry area due to evaporation or evapotranspiration of a water source or plant life and higher albedo of plant life than bare ground.
It is the exchange of heat whereby air over crop is cooled to supply heat for evaporation.

👉🏻 Isopleth is a line on a map connecting points having equal incidence of a specified meteorological feature.

Reported in terms of Octa wherein the sky is divided into 8 equal parts:

Pan Evaporimeter: used for estimating Evaporation under ﬁeld condition and scheduling of irrigation.
Portable Evaporimeter: developed in Israel, used to measure evaporation for short period.